Radiologic Findings
Chest Radiograph
•Normal, or
•Increased opacity (when atelectasis or consolidation are present)
If the ventilatory failure associated with myasthenia gravis is properly managed (e.g., via the Airway Clearance Therapy Protocol, Protocol 10.2, Ventilator Initiation and Management Protocol, Protocol 11.1, and Ventilator Weaning Protocol, Protocol 11.2), the chest radiograph should appear normal. However, if the patient is not properly managed, mucus accumulation, alveolar consolidation, and atelectasis may develop—as part of the myasthenic crisis. In these cases, the chest radiograph will show an increased density of the lung segments affected.
General Management of Myasthenia Gravis
In the past, many patients with myasthenia gravis died within the first few years of diagnosis of the disease. Today, a number of therapeutic measures provide most patients with marked relief of symptoms and allow them to live a normal life. Close respiratory monitoring with frequent measurements of the patient's forced vital capacity (FVC), maximum inspiratory pressure (MIP), maximum expiratory pressure (MEP), blood pressure, oxygen saturation, and, when indicated, arterial blood gases (ABGs) should be performed. Mechanical ventilation should be initiated when the clinical data demonstrate impending or acute ventilatory failure.
Good clinical indicators of impending acute ventilatory failure include the following:
•FVC less than 20 mL/kg
•MIP below –30 cm H2O—In other words, the patient is unable to generate a maximum
inspiratory pressure of –30 cm H2O or more. For example, an MIP of only –15 cm H2O would confirm severe muscle weakness and, importantly, that acute ventilatory failure is likely.
•MEP less than 40 cm H2O
•PaCO2 greater than 45 mm Hg
•pH less than 7.35
The four basic therapy modalities used to treat myasthenia gravis are (1) symptomatic treatment (acetylcholinesterase inhibitors), (2) chronic immunotherapies (e.g., glucocorticoids and other immunosuppressive drugs), (3) rapid immunotherapies (plasma exchange and intravenous immune globulins [IVIG]), and (4) thymectomy.
Symptomatic Treatment: Acetylcholinesterase Inhibitors
Acetylcholinesterase inhibitors are recommended as the first line of treatment for symptomatic myasthenia gravis. Pyridostigmine (Mestinon) is usually the first choice. Pyridostigmine inhibits the function of acetylcholinesterase. This action increases the concentration of ACh to compete with the circulating anti-ACh antibodies, which interfere with the ability of ACh to stimulate the muscle receptors. Although the anticholinesterase inhibitors are effective in mild cases of myasthenia gravis, they are not completely effective in severe cases.
Chronic Immunotherapies
Most patients with myasthenia gravis need some form of immunotherapy in addition to an acetylcholinesterase inhibitor (see previous section). It is recommended that immunotherapy be administered to patients who remain significantly symptomatic while on an acetylcholinesterase inhibitor or who become symptomatic after a temporary response to an acetylcholinesterase inhibitor. Common immunotherapy agents include glucocorticoids, azathioprine, mycophenolate mofetil, and cyclosporine. Immunotherapy agents are usually used for more severe cases. The patient's strength often improves strikingly with steroids. Patients receiving long-term steroid therapy, however, may develop serious complications such as diabetes, cataracts, steroid myopathy, gastrointestinal bleeding, infections, aseptic necrosis of the bone, osteoporosis, and psychoses.
Rapid Immunotherapies
Rapid immunotherapies are also immunomodulating, but are unique because of their quick onset, transient benefit, and use in select situations. These therapies are used most often for the following situations:
•Myasthenic crisis
•Preoperatively before thymectomy or other surgery
•As a bridge to slower acting immunotherapies
•To help maintain remission in hard-to-control patients.
Rapid immunotherapy modalities include plasmapheresis and IVIG therapy.
Plasmapheresis (plasma exchange) directly removes the AChR antibodies from the patient's blood. The beneficial effects of plasmapheresis basically correlate to the decrease in the AChR antibodies. Immunotherapy (e.g., glucocorticoids) is typically administered concurrently to offset an AChR antibody level rebound. Plasmapheresis is a well-established treatment selection for seriously ill patients in a myasthenic crisis. Plasmapheresis can be a life-saving intervention in the treatment of myasthenia gravis. However, it is time-consuming and is associated with many side effects, such as low blood pressure, infection, and blood clots.
Intravenous immune globulin (IVIG) entails the administration of pooled immunoglobulins (IgG) from multiple donors. Although the precise mechanism of IVIG therapy is uncertain, the benefits are typically seen in less than a week and can last for 3 to 6 weeks. Similar to plasmapheresis, IVIG therapy is used to quickly reverse an exacerbation of myasthenia gravis. IVIG therapy also provides an alternative to plasmapheresis or immunosuppressive agents in certain patients with refractory myasthenia gravis, or as a preoperative treatment before a thymectomy, or as a “bridge” to slower acting immunotherapy agents. Transfusion reactions to rapid administrations of IVIG are not uncommon.
Thymectomy
Although controversial, a thymectomy may be recommended for some patients with generalized myasthenia gravis who are younger than 60 years of age and without thymoma. The thymus is the source of the anti-ACh receptor antibodies. Although a thymectomy may improve muscle strength in some patients, the full benefits of this procedure usually take
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several years to accumulate.
Respiratory Care Treatment Protocols
Oxygen Therapy Protocol
Oxygen therapy is used to treat hypoxemia, decrease the work of breathing, and decrease myocardial work. Because of the hypoxemia that may develop in myasthenia gravis, supplemental oxygen may be required. However, because of the alveolar consolidation and atelectasis associated with myasthenia gravis, capillary shunting may be present. Hypoxemia caused by capillary shunting is refractory to oxygen therapy (see Oxygen Therapy Protocol, Protocol 10.1).
Airway Clearance Therapy Protocol
Because of the excessive mucous production and accumulation associated with myasthenia gravis, a number of airway clearance therapies may be used to enhance the mobilization of bronchial secretions (see Airway Clearance Therapy Protocol, Protocol 10.2).
Lung Expansion Therapy Protocol
Lung expansion measures are commonly administered to prevent or offset the alveolar consolidation and atelectasis associated with myasthenia gravis (see Lung Expansion Therapy Protocol, Protocol 10.3).
Mechanical Ventilation Protocol
Mechanical ventilation may be needed to provide and support alveolar gas exchange and eventually return the patient to spontaneous breathing. Because acute ventilatory failure is often seen in patients with severe myasthenia gravis, continuous mechanical ventilation may be required. Continuous mechanical ventilation is justified when the acute ventilatory failure is thought to be reversible. Noninvasive positive-pressure ventilation (NIPPV) may be helpful if carefully monitored (see Ventilator Initiation and Management Protocol, Protocol 11.1, and Ventilator Weaning Protocol, Protocol 11.2).
Case Study Myasthenia Gravis
Admitting History
A 35-year-old Spanish-American woman was a schoolteacher with a 3-year-old son and an unemployed husband who was still “finding his real place in life.” The woman was a high achiever. She had recently received her doctoral degree in education, but she continued to work in the classroom with the grade-school children she loved so much. She was named Teacher of the Year in the large city where she lived. Her colleagues at school considered her a nonstop worker. She had never smoked.
At home, she was always on the move. She had just finished remodeling her kitchen and two bathrooms. She also did her own backyard landscaping on the weekends, a job she particularly enjoyed. She read and played with her son whenever they had time together. Although she enjoyed cooking (a skill she learned from her mother), she did not like to shop for groceries. Fortunately, this was a chore that her husband enjoyed.
Three weeks before the current admission, the woman noticed that her eyes “felt tired.” She began to experience slight double vision. Thinking that she was working too hard, she slowed down a bit and went to bed earlier for about a week. However, she progressively felt weaker. Her legs quickly became tired, and she began having trouble chewing her food. Concerned, the woman finally went to see her doctor. After reviewing the woman's recent history and performing a careful physical examination, the physician admitted her to the hospital for further evaluation and treatment.
Over the next 48 hours, the woman's physical status declined progressively. At the patient's bedside, an ice pack test was positive for myasthenia gravis when her ptosis improved by 5 mm. She also indicated that her diplopia was better for about 10 minutes after the test. After the administration of edrophonium, her muscle strength increased significantly for about 10 minutes. Electromyography disclosed extensive muscle involvement and a high degree of fatigability in all the affected muscles. A diagnosis of myasthenia gravis was recorded in the patient's chart.
The woman began to choke and aspirate food during meals, and a nasogastric feeding tube was inserted. Her speech became increasingly more slurred. Both her upper eyelids drooped, and she was unable to hold her head off her pillow on request. The respiratory therapists who monitored her forced vital capacity, maximum inspiratory pressure, pulse oximetry, and arterial blood gas values (ABGs) reported a progressive worsening in all parameters.
When the woman's ABGs were pH 7.32, PaCO2 51 mm Hg, 
23 mEq/L, PaO2 59 mm Hg, and SaO2 88% (on room
air), the respiratory therapist called the physician and reported an assessment of acute ventilatory failure. The doctor had the patient transferred to the intensive care unit, intubated (no. 7 endotracheal tube with a tube length charted at 23 cm at the lip), and placed on a mechanical ventilator. The initial ventilator settings were synchronized intermittent mechanical ventilation (SIMV) mode, frequency 10 breaths/min, tidal volume 600 mL, FIO2 0.50, and positive end-expiratory pressure
(PEEP) of +5 cm H2O.
On these ventilator settings, her ABG values were pH 7.28, PaCO2 64 mm Hg, 
29 mEq/L, PaO2 52 mm Hg, and SaO2 81%. About 45 minutes after the patient was placed on the ventilator, she appeared agitated. No spontaneous
ventilations were seen. Her vital signs were blood pressure 132/86 mm Hg, heart rate 90 beats/min, and rectal temperature 38°C (100.5°F). A portable chest radiograph had been taken, but the image was still being processed. Normal vesicular breath sounds were auscultated over the right lung, and diminished-to-absent breath sounds were auscultated over the left lung. On the basis of these clinical data, the following SOAP was recorded.
Respiratory Assessment and Plan
S N/A (patient intubated)
O No spontaneous ventilations; vital signs: BP 132/86, HR 90, RR 10 (controlled), T 38°C (100.5°F); normal breath sounds over right lung; diminished-to-absent breath sounds over left
lung; ABGs (on FIO2 0.50) pH 7.28, PaCO2 64, 
29, PaO2 52, and SaO2 81%. A
•Myasthenic crisis
•Endotracheal tube possibly placed in right mainstem bronchi (diminished-to-absent breath sounds over left lung, ABGs)
•Acute ventilatory failure with moderate hypoxemia—on present ventilatory settings (ABGs)
• Worsening condition likely caused by misplacement of endotracheal tube
P Notify physician stat. Check CXR. Pull endotracheal tube back until breath sounds can be auscultated over both lungs. Confirm initial placement of the endotracheal tube when radiograph is available. Mechanical Ventilation Protocol (increase tidal volume to 750 mL and increase FIO2 to 1.0). Monitor and reevaluate immediately.
Forty-Five Minutes Later
After the patient's endotracheal tube was pulled back 3 cm to 20 cm at the lip, normal vesicular breath sounds could be auscultated over both lungs. The first chest radiograph examination confirmed that the endotracheal tube had indeed been inserted too far into the patient's right main-stem bronchus. A follow-up chest radiograph examination confirmed that the endotracheal tube was now appropriately positioned about 2 cm above the carina. Her vital signs were blood pressure 123/75 mm Hg, heart rate 74 beats/min, and temperature normal. On the new ventilatory settings per the last SOAP (see
earlier), the ABGs were pH 7.53, PaCO2 27 mm Hg, 
22 mEq/L, PaO2 376 mm Hg, and SaO2 98%. On the basis of these clinical data, the following SOAP was written.
Respiratory Assessment and Plan
S N/A (patient intubated on ventilator)
O Vital signs: BP 123/75, HR 74, T normal; normal bronchovesicular breath sounds over both lung fields; CXR: No. 7 endotracheal tube in good position (20 cm at lip); lungs adequately
ventilated; ABGs pH 7.53, PaCO2 27, 
22, PaO2 376, and SaO2 98%.
A Acute ventilator-induced alveolar hyperventilation (respiratory alkalosis), with overly corrected hypoxemia (ABGs)
P Adjust present settings per Mechanical Ventilation Protocol (decrease tidal volume to 650 mL). Down-regulate Oxygen Therapy Per Protocol (decrease FIO2 to 0.30). Monitor and
reevaluate (e.g., SpO2, maximum inspiratory pressure [MIP], and forced vital capacity (FVC) 2 × per shift).
Three Days Later
No changes in the patient's ventilator settings were made since the SOAP shown above. No remarkable information was noted during the past 72 hours. However, on this day the woman appeared pale and her vital signs were blood pressure 146/88 mm Hg, heart rate 92 beats/min, and temperature 37.9°C (100.2°F). Large amounts of thick, yellowish sputum were being suctioned from her endotracheal tube about every 30 minutes. No improvement was seen in her muscular paralysis.
Coarse crackles were auscultated over both lung fields. A sputum sample was obtained and sent to the laboratory to be cultured. A portable chest radiograph revealed a new infiltrate in the right lower lobe consistent with pneumonia or atelectasis. The ABGs (on FIO2 0.30, tidal volume 650 mL, respiratory rate of 10, and PEEP of +5) were pH 7.28, PaCO2
36 mm Hg, 
16 mEq/L, PaO2 41 mm Hg, and SaO2 69%. On the basis of these clinical data, the following SOAP was recorded.
Respiratory Assessment and Plan
S N/A
O No improvement seen in muscular paralysis; skin: pale; vital signs: BP 146/88, HR 92, T 37.9°C (100.2°F); large amounts of thick, yellowish sputum; coarse crackles over both lung
fields. CXR: Pneumonia and atelectasis in right lower lobe. ABGs pH 7.28, PaCO2 36, 
16, PaO2 41, and SaO2 69%.
A
•Excessive bronchial secretions (coarse crackles, sputum)
•Infection likely (yellow sputum, fever, CXR: pneumonia)
•Metabolic acidosis with moderate to severe hypoxemia (ABGs)
•Acidosis likely caused by lactic acid (ABGs)
P Up-regulate Airway Clearance Therapy Protocol (med. neb. with 0.5 mL albuterol in 2 mL normal saline, q4h; therapist to suction patient frequently; sputum culture check in 24 and 48 hours). Up-regulate Lung Expansion Therapy Protocol (+10 cm H2O PEEP). Up-regulate
Oxygen Therapy Protocol (increase FIO2 to 0.60). Monitor closely and reevaluate (check ABGs in 30 minutes).
Discussion
As with the patient with Guillain-Barré syndrome, this case of myasthenia gravis provides another chance to discuss ventilatory failure secondary to neuromuscular disease. The presentation of this patient with double vision (diplopia), difficulty in swallowing (dysphagia), and progressive muscle weakness is classic for this condition. The positive edrophonium test noted in the history was necessary for a final diagnosis. Also important to note is that aspiration of gastric contents is not uncommon in such cases.
In the first assessment the therapist correctly recognized that this case was more than simple respiratory failure. The reader sees that the patient was intubated and that breath sounds no longer were present in the entire left lung (inadvertent right mainstem bronchial intubation). The therapist appropriately responded quickly and pulled the endotracheal tube back until breath sounds could be auscultated over both lung fields. The inappropriate positioning of the tube was confirmed 45 minutes later in the patient's chest radiograph. The patient's respiratory status could have been seriously compromised if the therapist had waited a full 45 minutes before pulling the tube above the carina. This event further demonstrates the importance of good bedside assessment skills. In addition, because lactic acidosis was probably
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present at this time, oxygenating the patient was of primary importance. In fact, increasing the FIO2 to 1.0 would have
been appropriate in this case.
The second assessment reflected that the patient was improving and was now hyperventilated and hyperoxygenated on the current ventilator settings. The therapist adjusted the ventilator settings accordingly and began the process of longitudinal evaluation of forced vital capacity and maximum inspiratory pressure so that the Mechanical Ventilation Protocol was appropriate for this condition.
The final assessment suggested that the patient had taken another turn for the worse. The sputum was now purulent, coarse crackles were heard over both lung fields, and a right lower lobe pneumonia or atelectasis had developed. The patient had an uncompensated metabolic acidemia that required evaluation. The fact that the patient's PaO2 was only 41
provided a significant clinical indicator that the cause of the metabolic acidosis was probably lactic acid generated from a low tissue oxygen level. It was clearly appropriate for the respiratory therapist to focus on the patient's oxygenation status. This was done by up-regulating the Oxygen Therapy Protocol (Protocol 10.1) (increasing the FIO2 to 0.60) and starting the
Lung Expansion Therapy Protocol (Protocol 10.3) (the addition of 10 cm H2O PEEP to ventilator settings).
The therapist should have anticipated this development, obtained appropriate cultures, and, if not done before, prophylactically started the Airway Clearance Therapy Protocol (Protocol 10.2) and Aerosolized Medication Therapy Protocol (Protocol 10.4)—with frequent suctioning, percussion, postural drainage, and possibly mucolytics. Finally, for a better understanding of lactic acidosis, the reader may wish to review other possible causes of metabolic acidemia at this time (e.g., diabetic ketoacidosis, renal failure) (see Chapter 5, Blood Gas Assessment).
Unfortunately the patient's pulmonary condition progressively deteriorated, and she died 3 weeks later.
Self-Assessment Questions
1.The onset of the signs and symptoms of myasthenia gravis is(are):
1.Slow and insidious
2.Sudden and rapid
3.Intermittent
4.Often elusive
a.1 only
b.2 only
c.2 and 4 only
d.1, 2, 3, and 4
2.Myasthenia gravis:
1.Is more common in young men
2.Has a peak age of onset in females of 15 to 35 years
3.Is often provoked by emotional upset and physical stress
4.Is associated with receptor-binding antibodies
a.1 only
b.2 and 4 only
c.2, 3, and 4 only
d.1, 2, 3, and 4
3.Which of the following is associated with myasthenia gravis? 1. Bronchospasm
2.Mucus accumulation
3.Alveolar hyperinflation
4.Atelectasis
a.1 and 2 only
b.2 and 4 only
c.1, 2, and 4 only
d.2, 3, and 4 only
4.When monitoring the patient with myasthenia gravis, all of the following are indicators of acute ventilatory failure except:
a.pH: 7.31
b.PaCO2: 55 mm Hg
c.FVC: 25 mL/kg
d.MIP: –15 cm H2O
5.Which of the following antibodies is believed to block the nerve impulse transmissions at the neuromuscular junction in myasthenia gravis?
a.IgG
b.IgE
c.IgA
d.IgM
1It should be noted that the clinical manifestations associated with myasthenia gravis may occur over hours or days, depending on how quickly the paralysis progresses.
C H A P T E R 3 1
Cardiopulmonary Assessment and Care of Patients with Neuromuscular Disease
CHAPTER OUTLINE
Chronic Neuromuscular Diseases
Spinal Cord Injury
Amyotrophic Lateral Sclerosis
Muscular Dystrophies
Stroke
Head Injury
Overview of the Cardiopulmonary Manifestations Associated With Neuromuscular Diseases
General Management of Neuromuscular Disease
Nutrition
Ventilatory Management of Patients With Neuromuscular Diseases
Tracheostomy
Ventilatory Support
Case Study: Amyotrophic Lateral Sclerosis
Self-Assessment Questions
CHAPTER OBJECTIVES
After reading this chapter, you will be able to:
•Describe the etiology and epidemiology of various neuromuscular diseases, including spinal cord injury, amyotrophic lateral sclerosis, stroke, muscular dystrophy, and head injury.
•List the cardiopulmonary manifestations associated with neuromuscular diseases.
•Describe the general management of neuromuscular diseases.
•Describe strategies for the respiratory care of patients with neuromuscular disease.
•Describe the clinical strategies and rationales of the SOAPs presented in the case studies.
•Define key terms and complete self-assessment questions at the end of the chapter and on Evolve.
KEY TERMS
Amyotrophic Lateral Sclerosis (ALS)
Ataxic (Biot)
Bi-level Positive Airway Pressure (BPAP)
Breath Stacking
Bulbar Dysfunction
Cerebral Perfusion Pressure (CPP)
Cheyne-Stokes Respiration
Diaphragm Pacing
Duchenne Muscular Dystrophy (DMD)
Dysarthria
Dysphagia
Emery-Dreifuss Muscular Dystrophy
Facioscapulohumeral Dystrophy (FSHD)
Gower's Sign
Intracranial Pressure (ICP) Monitoring
Intubation Risk
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Leak Speech
Limb-Girdle Muscular Dystrophy (LGMD) Mouthpiece Ventilation (MPV)
Muscle Biopsy Muscular Dystrophy Myotonic Dystrophy
Neuromuscular Disease (NMD) Obesity
Oropharyngeal Dysphagia Paradoxical Abdominal Breathing Pseudobulbar Palsy
Pseudohypertrophy of the Calf Muscles Rapid Sequence Intubation (RSI) Sialorrhea
Speaking Valve
Spinal Cord Injury (SCI) Stroke
Talking Tracheostomy Tubes Transient Ischemic Attacks (TIAs) Tissue Plasminogen Activator (tPA)
Video-Assisted Thorascopic Surgery (VATS)
Volume-Assured Pressure Support (VAPS)
Neuromuscular disease (NMD) is a generalized term used to describe disorders of the brain, spinal cord, peripheral nerves, neuromuscular junction, and muscles. These disorders are associated with a wide range of motor and sensory deficits; however, patients with NMD may develop significant cardiopulmonary issues. In fact, breathing disorders are the leading cause of death in patients with NMD. Thus it is important for the respiratory therapist to be familiar with these conditions and their effect on the respiratory system. Table 31.1 includes a list of acute and chronic NMDs that affect the respiratory system. This chapter will focus specifically on spinal cord injury, amyotrophic lateral sclerosis, muscular dystrophies, stroke, and head injuries. Other neuromuscular disorders will be covered in other chapters.
TABLE 31.1
Acute and Chronic Neuromuscular Diseases That Affect the Respiratory System
Cerebral |
Brainstem/Basal |
Spinal Cord |
Motor |
Neuromuscular |
Myopathies |
Nerves/Anterior |
Cortex |
Ganglia |
|
Horn Cell |
Junction |
|
|
|
|
|
|
Stroke (acute) |
Stroke (acute) |
Trauma (acute) |
Motor neuron |
Myasthenia gravis |
Muscular |
|
|
|
disease |
|
dystrophies |
Malignancy |
Malignancy |
Infarction |
Postpolio |
Lambert-Eaton |
Polymyositis |
|
|
|
syndrome |
myasthenic syndrome |
|
Seizures |
Central alveolar |
Hemorrhage |
Amyotrophic |
Drugs |
Dermatomyositis |
|
hypoventilation |
|
lateral sclerosis |
Antibiotics |
|
|
|
|
|
Anticholinesterase |
|
|
|
|
|
inhibitors |
|
|
|
|
|
Corticosteroids |
|
|
|
|
|
Lithium |
|
Cerebral |
Multiple system |
Disk |
Vasculitis |
|
|
degeneration |
atrophy |
compression |
|
|
|
|
Parkinson disease |
Malignancy |
Spinal muscular |
|
|
|
|
|
atrophy |
|
|
|
Dyskinesias |
Demyelinating |
Metabolic |
|
|
|
|
disease |
disorders |
|
|
Chronic Neuromuscular Diseases
Spinal Cord Injury
Etiology and Epidemiology
Spinal cord injury (SCI) is a relatively common and devastating event associated with significant morbidity and mortality (Fig. 31.1). According to the National Spinal Cord Injury Statistical Center (NSCSC) in 2018, the annual incidence of spinal cord injury (SCI) was about 17,700 new cases each year. New SCI cases do not include those who die at the location of the indecent that caused the SCI. The number of people with SCI living in the United States is currently estimated to be approximately 288,000 persons. The average age at injury has increased from 29 years during the 1970s to 43 years currently. About 78% of new SCI cases are male. Vehicle crashes are currently the leading cause of SCI injuries, closely followed by falls. Acts of violence (primarily gunshot wounds) and sports/recreation activities are also relatively common causes. Table 31.2 lists causes of nontraumatic SCI.
FIGURE 31.1 A 53-year-old man who sustained a severe T4 vertebral injury after a motor vehicle collision. Note the anterior displacement of the thoracic spine (red arrow) and the fracture of the spinous process (green arrow).
TABLE 31.2
Nontraumatic Causes of Spinal Cord Injury
Congenital |
Spinal dysraphism |
|
Arnold-Chiari malformations |
|
Skeletal malformations |
|
Syringomyelia |
Genetic |
Hereditary spastic paraplegias |
|
Spinal muscular atrophies |
|
Adrenoleukodystrophy |
|
Amyotrophic lateral sclerosis |
|
Friedreich ataxia |
Acquired |
Malignancy |
|
Paraneoplastic syndromes |
|
Infections |
|
Degenerative vertebral disease |
|
Vascular disorders |
|
Spinal cord infarction |
|
Vascular malformations |
|
Spinal epidural hematoma |
|
Autoimmune disorders |
|
Transverse myelitis |
|
Sarcoidosis |
|
Toxic-metabolic disorders |
|
Radiation myelopathy |
|
Copper deficiency |
|
Decompression sickness myelopathy |
|
Subacute combined degeneration |
|
Hepatic myelopathy |
|
Vitamin C deficiency |
Clinical Presentation
Patients with disorders of the spinal cord will present with a variety of clinical signs and symptoms that vary depending on the level of injury. Damage to the lumbosacral spinal cord results in lower extremity weakness/paralysis, spasticity, and dysfunction of the bowel and bladder. Cervical nerves C3 through C5 innervate the diaphragm via the phrenic nerve. Thus injuries at or above this level will result in significant respiratory compromise and even death without immediate intervention. Thoracic cord injuries will have lower extremity symptoms as well; however, despite sparing the phrenic nerve, injuries at this level can affect breathing by impairing function of respiratory muscles. Impairment of these muscles will also contribute to poor coughing, which can increase the risk for developing pulmonary infections. These muscles are displayed in Fig. 31.2.
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FIGURE 31.2 The muscles of respiration. (From Patton, K. T., Thibodeau, G. A., & Douglas, M. M. (2012). Essentials of anatomy and physiology. St. Louis, MO: Elsevier.)
Additionally, the rib cage stiffens in the months after an SCI. This results in decreased thoracic compliance and atelectasis, with an increased compliance of the abdomen. Patients with cervical or thoracic injuries may develop a rapid shallow breathing pattern and a paradoxical abdominal breathing pattern in which the chest wall moves inward during inspiration because of isolated diaphragmatic breathing. Autonomic dysfunction is also common in patients with SCI and can manifest as hypotension, hypertensive crises, and tachycardia.
The American Spinal Injury Association (ASIA) Impairment Scale classifies the extent of SCIs into the following categories:
A = Complete: No sensory or motor function is preserved in sacral segments S4-S5.
B = Incomplete: Sensory, but not motor, function is preserved below the neurologic level and extends through sacral segments S4-S5.
C = Incomplete: Motor function is preserved below the neurologic level, and most key muscles below the neurologic level have a muscle grade less than 3.
D = Incomplete: Motor function is preserved below the neurologic level, and most key muscles below the neurologic level have a muscle grade that is 3 or greater.
E = Normal: Sensory and motor functions are normal.
Diagnosis
SCIs may not always be readily recognizable. Evaluation for possible SCI should be performed in patients who experience traumatic injuries, including head injuries, pelvic fractures, penetrating injuries involving the spine, and falls from heights. X-rays are a quick, portable, and inexpensive way to evaluate the bony structures of the spine. However, they are insensitive for diagnosing most disorders of the spinal column. Computed tomography (CT) scanning of the spine can be used to identify vertebral fractures (see Fig. 31.1), epidural hematomas and fluid collections, and other injuries involving the spinal cord. It can be done quickly, which makes it an appropriate initial evaluation in patients with suspected spinal injury. Magnetic resonance imaging (MRI) is much more sensitive and better evaluates the spinal cord, nerve roots, ligaments, and disk spaces compared with CT. Electromyography and nerve conduction studies are generally unnecessary to make the diagnosis.
Management
The treatment of SCIs involves a multidisciplinary approach. Prompt assessment is important to prevent additional injury and initiate the appropriate treatment in a timely fashion. Comorbid injuries, such as abdominal or thoracic trauma, should be sought and managed accordingly. Maintaining proper cervical alignment using skull traction or other forms of mechanical stabilization will help prevent secondary injury and improve prospects for recovery. Specific injuries may be best treated with prompt surgical intervention by a neurosurgeon or orthopedic surgeon who is trained in the management of SCIs.
Autonomic dysfunction may require intravenous fluid resuscitation and possibly vasoactive medications to maintain adequate tissue perfusion. Anticoagulation should be initiated to prevent venous thromboembolism. Those with neurogenic bowel and bladder will require assistance with defecation and urination. Flaccid rectal tone may necessitate the use of digital rectal stimulation, suppositories, or enemas to treat constipation. Repeated bladder catheterization or insertion of a chronic indwelling suprapubic catheter may be considered.
Patients with injuries below the level of C5 generally do not require ventilatory support; however, significant injuries at the C5 level and above will have diaphragmatic impairment (and impairment of other respiratory muscles) necessitating additional respiratory support. Intubation and mechanical ventilation should be instituted in patients with evidence of impending respiratory failure, including tachypnea, rising PaCO2 levels, and hypoxemia. Manual or mechanically assisted
coughing, respiratory physiotherapy, and breathing exercises can help clear bronchial secretions and prevent pulmonary infection. An abdominal binder can be used to decrease work of breathing by reducing the paradoxical breathing pattern.
The intubation risk for patients with cervical SCIs is significant. Extension of the neck can lead to worsening cervical injury. Additionally, patients with traumatic cervical SCIs may have facial trauma that will make orotracheal intubation difficult. It is not uncommon for these patients to require emergent tracheostomy placement for further long-term airway management.
Diaphragm pacing is a potential treatment option for selected patients with SCI who are dependent on mechanical ventilation. It can be an effective modality to eliminate the need for or reduce dependence on mechanical ventilation. A thoracic surgeon may perform a laparoscopy to place electrodes within the muscle of the diaphragm or use video-assisted thorascopic surgery (VATS) to place leads directly on the phrenic nerve. These electrodes are connected to an external transmitting box that can be used to control the frequency, amplitude, and duration of pacing. Once the device is placed, the patient will undergo a conditioning period of weeks to months during which the pacemaker settings are adjusted based on minute ventilation, gas exchange, and patient comfort. The optimal timing for evaluation is unknown; however, it is generally accepted that patients with a cervical SCI should not be evaluated until at least 3 months after their injury because there may be partial or complete recovery of phrenic nerve function. Diaphragm pacing is challenging when the phrenic nerve or the diaphragm is not functional, and phrenic nerve transplantation has poor success rates at this time. Much of the experience with diaphragm pacing comes from observational studies and published case series.
Amyotrophic Lateral Sclerosis
Etiology and Epidemiology
Amyotrophic lateral sclerosis (ALS) is a progressive neurologic disorder characterized by degeneration of upper and lower motor neurons. The disease is also known as Lou Gehrig disease, named after the famous baseball player who was diagnosed with this condition in the 1930s.
The exact cause is unknown; however, research has suggested that the pathogenesis of ALS centers around genetic mutations in genes involved in protein homeostasis, RNA homeostasis and trafficking, and cytoskeletal dynamics. Both familial and sporadic cases have been reported and have similar pathologic features. The National ALS Registry estimates that the overall prevalence of ALS in the United States is 4.7 to 5.0 per 100,000 people. In Europe and the United States, there are approximately 1 or 2 new cases of ALS per year per 100,000 people. The majority of new cases are sporadic in origin, with only about 10% being familial. The average survival time from diagnosis to death is 3 to 5 years. The leading cause of death in ALS is respiratory failure.
Clinical Presentation
ALS affects both upper and lower motor neurons. The disorder typically begins with limb findings (arm or leg weakness, gait instability, etc.); however, up to one-third of patients present with bulbar findings such as dysphagia, dysarthria (difficulty with speech), and difficulty chewing. Table 31.3 lists common neurologic findings in patients with ALS. Pseudobulbar palsy, characterized by emotional lability, facial spasticity, and inappropriate laughing or crying, suggests involvement of the frontopontine motor neurons. The disease typically involves the diaphragm and can cause dyspnea, impaired cough, and respiratory failure. Cognitive symptoms also may be present. It is important to note that there are several variants of ALS that have different presentations, including isolated bulbar ALS, brachial amyotrophic diplegia (“man-in-the-barrel syndrome”), and leg amyotrophic diplegia. Patients can present with purely upper motor neuron (UMN) or lower motor neuron (LMN) signs and symptoms. ALS-plus syndrome encompasses the same UMN and LMN findings as ALS accompanied by other disorders, including frontotemporal dementia, autonomic insufficiency, Parkinsonism, and/or sensory loss.
TABLE 31.3
Neurologic Signs and Symptoms in Amyotrophic Lateral Sclerosis
|
Upper Motor Neuron |
Lower Motor Neuron |
Limb findings |
Limb spasticity |
Fasciculations |
|
Limb weakness |
Gait disorder |
|
Spastic gait |
Muscle atrophy |
|
Incoordination of movements |
Foot drop |
|
Spontaneous clonus |
Poor rise from chair |
|
Spontaneous flexor spasms |
Cramps |
|
Increased reflexes |
|
|
“Preserved” reflexes in weak/atrophic muscles |
|
|
Hoffman sign |
|
|
Upgoing toe |
|
|
Distal spread of arm reflexes |
|
|
Triple flexion |
|
Bulbar findings |
Spastic dysarthria |
Tongue wasting |
|
Brisk gag and jaw reflex |
Tongue weakness |
|
Facial asymmetry |
Tongue fasciculations |
|
Increased facial reflexes |
Nasal speech |
|
Slow tongue movement |
Hoarse speech |
|
Dysphagia |
Weak cough |
|
Laryngospasm |
Difficulty maintaining jaw closure |
|
Pseudobulbar affect |
Incomplete eye closure |
|
Mood incongruent |
Poor lip closure and seal |
|
Inappropriate laughing, crying, and/or yawning |
Difficulty chewing |
|
Sialorrhea (drooling) |
|
|
Difficulty managing secretions |
|
Diagnosis
The diagnosis of ALS is typically made on clinical grounds. There are no laboratory or other diagnostic markers that are pathognomonic for ALS. Multiple diagnostic criteria exist. However, the most widely accepted and validated criteria are the revised El Escorial World Federation of Neurology criteria. The diagnosis of ALS requires the evidence of LMN degeneration, the presence of UMN degeneration, and progressive spread of symptoms or signs within a region or to other regions as determined by history of physical examination. LMN and UMN degeneration may be identified by clinical examination, electrophysiologic testing, or neuropathologic examination. Furthermore, electrophysiologic or pathologic evidence of other disease processes that can explain the LMN and/or UMN degeneration and neuroimaging evidence of another disease process that could explain the clinical and electrophysiologic findings must be absent. In the absence of pathologic confirmation, the certainty of the diagnosis may be classified as clinically definite, clinically probable, and clinically possible ALS. This diagnostic approach has been validated pathologically and has been shown to have acceptable interobserver agreement. It is important to note that as many as 21% of patients die from ALS without ever meeting the revised El Escorial criteria. Some patients, particularly those in the intensive care unit, may not be able to undergo electromyography and nerve conduction studies or may not have access to a neurologist to perform the necessary evaluation. For a respiratory therapist, sialorrhea (drooling) and tongue fasciculations are two important clinical cues that should prompt one to consider a diagnosis of ALS.
Electromyography will demonstrate signs of acute and chronic denervation. Nerve conduction studies are often normal, but compound motor action potential amplitudes may be reduced in more severe disease. Repetitive nerve stimulation,
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which assesses the integrity of the neuromuscular junction, may be normal or abnormal in ALS, but it remains a useful test to help exclude diseases that primarily target the neuromuscular junction such as myasthenia gravis or Lambert-Eaton myasthenic syndrome (see Chapter 30). MRI of the brain and spinal cord is helpful to exclude other disorders that may manifest with UMN findings.
Muscle biopsy is not a routine test performed in the diagnosis of ALS, but it may be performed to exclude other diagnoses that cause myopathy. Small, angular fibers are indicative of neurogenic atrophy. There also may be findings consistent with reinnervation. These findings are not specific for ALS.
Management
There is currently no cure for ALS. Riluzole is a medication that has been shown to slow ALS disease progression. Its exact mechanism of action in ALS is unknown; however, experimental data suggest that riluzole has effects on neural activity. Riluzole is thought to inhibit glutamate-induced excitotoxicity by inhibiting neurotransmitter release, antagonizing N- methyl-D-aspartate (NMDA) receptors, and inhibiting the action of sodium channels. The American Academy of Neurology recommends riluzole for patients with definite or probable ALS who have had symptoms less than 5 years, have a vital capacity greater than 60% of predicted, and do not have a tracheostomy. Potential side effects include asthenia, dizziness, elevated liver enzymes, gastrointestinal upset, weakness, worsening muscular weakness. Edaravone (Radicava) is a new intravenous medication approved by the US Food and Drug Administration for treatment of ALS. Its mechanism of action is unknown. It has been shown to slow the decline in physical function; however, edaravone has not been shown to improve respiratory parameters in patients with ALS.
Symptom management involves close monitoring of respiratory function to determine the appropriate timing to initiate supportive ventilation. Airway clearance therapy to assist cough and improve clearance of secretions will help reduce the incidence of pneumonia. Management of comorbid conditions, including insomnia, depression, pain, and sialorrhea, is also important. Patients should have discussions regarding their goals of care and advance directives early in the course of the disease. Referral to hospice care is advised in the terminal phase of disease.
Muscular Dystrophies
Etiology, Epidemiology, and Clinical Presentation
Muscular dystrophy is a term that is composed of several genetic disorders characterized by pathologic changes within muscles affecting the limbs, face, and sometimes respiratory and cardiac muscles as well. They are distinguished from other neuromuscular disorders in that they are primary myopathies, are progressive, manifest degeneration of muscle fibers pathologically, and have a genetic origin. Muscular dystrophies may manifest at different times throughout life with different degrees of severity. These disorders can be transmitted as autosomal dominant, autosomal recessive, or X-linked traits. Sporadic cases can occur as well. Table 31.4 lists different forms of muscular dystrophy and their typical age of onset, clinical manifestations, and life expectancies. Advances in medical therapy, particularly in the management of respiratory and cardiac complications, have resulted in significant increases in life expectancy for many of these patients.
TABLE 31.4
Muscular Dystrophies
|
|
Inheritance |
Onset of |
Pattern of |
Extraskeletal |
Life |
|
Disease |
Skeletal Muscle |
|
Pattern |
Symptoms |
Manifestations |
Expectancy |
|
|
Involvement |
|
|
|
|
|
|
|
Duchenne muscular |
XLR |
1–3 yr |
Proximal muscle |
Cardiomyopathy, intellectual |
40–50 yr |
|
dystrophy |
|
|
weakness and |
impairment, seizures, |
|
|
|
|
|
lower limbs |
autism-like behavior, |
|
|
|
|
|
affected first, |
respiratory failure |
|
|
|
|
|
followed by |
|
|
|
|
|
|
upper limbs and |
|
|
|
|
|
|
distal muscles |
|
|
|
Becker muscular |
XLR |
Childhood to |
Proximal muscles |
Dilated cardiomyopathy, |
30–50 yr |
|
dystrophy |
|
early 20s |
|
respiratory failure |
|
|
Myotonic dystrophy |
AD |
Childhood to |
Type 1: Facial, |
Cardiac arrhythmias, |
Mildly |
|
|
|
adulthood |
neck, forearm, |
hypersomnia, excessive |
reduced |
|
|
|
(depending |
hand, foot |
daytime sleepiness, |
(type 1) |
|
|
|
on size of |
dorsiflexor |
primary hypogonadism, |
Normal |
|
|
|
trinucelotide |
Type 2: Neck |
dysphagia, gallbladder |
(type 2) |
|
|
|
repeat) |
flexor, elbow |
disease, cognitive |
|
|
|
|
|
extensor, finger |
dysfunction, cataracts, |
|
|
|
|
|
flexor, hip |
abnormal liver function, |
|
|
|
|
|
flexor |
hypogammaglobulinemia, |
|
|
|
|
|
|
premature balding |
|
|
Emery-Dreifuss |
XLR |
5–15 yr |
Humeroperoneal |
Dilated cardiomyopathy, |
Variable |
|
muscular dystrophy |
AD/AR |
|
distribution |
arrhythmia, stroke |
|
|
|
forms |
|
|
|
|
|
|
are rare |
|
|
|
|
|
Limb-girdle muscular |
AD, AR |
Childhood to |
Scapulohumeral, |
Cardiomyopathy, |
Variable |
|
dystrophies |
|
adulthood |
pelvifemoral, or |
arrhythmias |
|
|
|
|
|
both |
|
|
|
Facioscapulohumeral |
AD |
Late childhood |
Facial, shoulder |
Arrhythmia, cognitive |
Normal |
|
muscular dystrophy |
|
to middle |
girdle (scapular |
impairment, hearing loss, |
|
|
|
|
adulthood |
winging), foot |
epilepsy, retinal |
|
|
|
|
|
extensors, pelvic |
vasculopathy, pain |
|
|
|
|
|
girdle |
|
|
|
Oculopharyngeal |
AD; AR form |
Third decade of |
Extraocular, |
Dysphagia, ptosis |
Normal |
|
Muscular Dystrophy |
is less |
life |
pharyngeal |
|
|
|
|
common |
|
|
|
|
AD, Autosomal dominant; AR, autosomal recessive; XLR, X-linked recessive.
Duchenne muscular dystrophy (DMD) is the most common inherited neuromuscular disorder. Guillaume Benjamin Amand Duchenne de Boulogne, a French neurologist, was the first to describe the disease when he reported a series of 13
