Color Atlas of Neurology
.pdfPeripheral Neuropathies
Radial nerve pressure palsy
Dorsiflexor weakness, pes cavus |
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Distal |
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muscle |
Peroneal nerve |
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paresis and |
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pressure palsy |
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atrophy |
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HMSN type I Thickened nerve |
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HNPP
Amyloid deposits (sural nerve, Congo red staining)
Foot ulcer/mutilation
Hereditary sensory neuropathy type I
Green birefringence (polarized light)
Amyloid neuropathy
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Demyelination of |
Darkening of urine |
white matter |
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β-aminolevulinic |
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acid, |
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porphobilinogen) |
Metachromatic |
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Porphyric attack |
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leukodystrophy |
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(acute intermittent porphyria) |
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(axial T1-weighted MRI scan) |
Peripheral Nerve and Muscle
333
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Peripheral Nerve and Muscle
334
Myopathies
Myopathic Syndromes
Myopathies are diseases of muscle. Many different hereditary and acquired diseases attack muscle, sometimes in combination with other organs. The diagnosis and classification of the myopathies have been transformed in recent years by the introduction of molecular biological tests for the hereditary myopathies, but their treatment remains problematic. The management of the hereditary myopathies currently consists mainly of genetic counseling and the attempt to provide an accurate prognosis.
!Symptoms and Signs (Table 64, p. 397)
Weakness (p. 52) is the most common sign of myopathy; it may be of acute, rapidly progressive, or gradual onset, fluctuating, or exerciseinduced. It may be local (restricted to the muscles of the eye, face, tongue, larynx, pharynx, neck, arms, legs, or trunk), proximal, or distal, asymmetric or symmetric. Myalgia, muscle stiffness, and muscle spasms are less common. There may be muscle atrophy or hypertrophy, often in a typical distribution, whose severity depends on the type of myopathy. Skeletal deformity and/or abnormal posture may be a primary component of the disease or a consequence of weakness. Other features include acute paralysis, myoglobulinemia, cardiac arrhythmia, and visual disturbances.
!Causes
For a list of causes of hereditary and acquired myopathies, see Tables 65 and 66, p. 398.
! Diagnosis (Table 67, p. 399)
The myopathies are diagnosed primarily by history and physical examination (p. 52). Pharmacological tests are used for the differential diagnosis of myasthenia. Neurophysiological studies are used to rule out neuropathy (p. 391), to determine the specific type of acute muscle change, or to identify disturbances of muscular impulse generation and conduction. Various laboratory tests are helpful in myopathies due to biochemical abnormalities; imaging studies of muscle aid in the differential diagnosis of atrophy and hypertrophy. Muscle biopsy is often needed for a definitive diagnosis. Molecular biological studies are used in the diagnosis of hereditary myopathies.
Rohkamm, Color Atlas of Neurology © 2004 Thieme
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Myopathies
Sympathetic trunk
Myelinated nerve fiber
Neuromuscular synapse (motor end plate)
Muscle fiber
Connective Blood tissue vessel
Lack of head and trunk control (congenital myopathy)
Spinal nerve
Thinly myelinated nerve fibers
Nerve fiber bundle
Blood vessel
Structures involved in neuromuscular disturbances
Weakness in pelvic girdle and thigh (Gowers’ sign)
Myotonic reaction (adduction of thumb on thenar percussion)
Weakness in shoulder girdle and upper arm |
Weakness of facial muscles with |
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myopathic facies (ptosis, attenuated |
Signs of myopathy |
facial expression, looks tired) |
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Peripheral Nerve and Muscle
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Myopathies
Muscular Dystrophies
The muscular dystrophies—myopathies characterized by progressive degeneration of muscle— are mostly hereditary.
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! Pathogenesis (Table 65, p. 398) |
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Dystrophinopathies are X-linked recessive dis- |
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orders due to mutations of the gene encoding |
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Muscle |
dystrophin, a protein found in the cell mem- |
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brane (sarcolemma) of muscle fibers. Such mu- |
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tations cause a deficiency, alteration, or absence |
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of dystrophin. The functional features of dystro- |
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phin are not fully understood; it is thought to |
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have a membrane-stabilizing effect. Some forms |
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Nerve |
of limb |
girdle dystrophy (e. g., |
sarcogly- |
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canopathy) are due to mutation of genes encod- |
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Peripheral |
ing dystrophin-associated glycoproteins, while |
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others are due to mutation of genes encoding in- |
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tracellular enzymes such as calpain-3. Emery– |
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Dreifuss muscular dystrophy is due to a mutation |
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of the gene for emerin, a nuclear membrane pro- |
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tein whose exact function is unknown. |
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! Symptoms and Signs |
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Muscular dystrophies may be characterized by |
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atrophy, |
hypertrophy, |
or |
pseudohypertrophy |
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and are further classified by their mode of in- |
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heritance, age of onset, and distribution. Other |
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features such as myocardial involvement, con- |
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tractures, skeletal deformity, endocrine dys- |
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function, and ocular manifestations may point |
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to one or another specific type of muscular dys- |
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trophy. Each type has a characteristic course |
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(Table 68, p. 400). |
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! Diagnosis |
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The history and physical examination are |
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supplemented by additional diagnostic studies |
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including ECG, creatine kinase fractionation |
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(CK-MM), EMG, and DNA studies. If DNA analy- |
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sis fails to reveal a mutation, immunohisto- |
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chemical techniques, immune blotting, or the |
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polymerase chain reaction can be used to detect |
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abnormalities of dystrophin and sarcoglycan |
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(e. g., in muscle biopsy samples) and thereby |
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distinguish between Duchenne and Becker |
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muscular |
dystrophy, |
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between |
dystro- |
336phinopathies and other forms of muscular dystrophy. DNA tests are used for the identification
of asymptomatic female carriers (in whom
muscle biopsy is hardly ever necessary), and for prenatal diagnosis.
! Treatment
The goal of treatment is to prevent contracture and skeletal deformity and to keep the patient able to sit and walk for as long as possible. The patient’s diet should be monitored to prevent obesity. The most important general measures are genetic counseling, social services, psychiatric counseling, and educating the patient on the special risks associated with general anesthesia. The type of schooling and employment must be appropriately suited to the patient’s individual abilities and prognosis. Physical therapy includes measures to prevent contractures, as well as breathing exercises (deep breathing, positional drainage, measures to counteract increased inspiratory resistance). Patients with alveolar hypoventilation may need intermittent ventilation with continuous positive airway pressure (CPAP) at night. Orthoses may be helpful, depending on the extent of weakness (night splints to prevent talipes equinus, seat cushions, peroneal springs, orthopedic corsets, leg orthoses). Home aids may be needed as weakness progresses (padding, eating aids, toilet/bathing aids, stair-lift, mechanized wheelchair, specially adapted automobile). Surgery may be needed to correct scoliosis, prevent contracture about the hip joint (iliotibial tract release), and correct winging of the scapula (scapulopexy/scapulodesis) and other deformities and contractures. Intracardiac conduction abnormalities (e. g., in Emery–Dreifuss muscular dystrophy) require timely pacemaker implantation. Heart transplantation may be needed when severe cardiomyopathy arises in conjunction with certain types of muscular dystrophy (Becker, Emery– Dreifuss; Table 68, p. 400).
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Myopathies
Sarcotubular system |
Dystroglycan Extracellular matrix, |
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Merosin |
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complex |
basal lamina |
Proximal |
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Mitochondria |
Laminin-2 |
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muscle |
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Sarcolemma |
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Sarcoglycan |
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Syntrophins |
weakness |
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complex |
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Sarcolemma |
Hyper- |
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Dystrobrevin |
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lordosis |
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F-Actin |
Dystrophin |
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Calpain-3 |
Proximal |
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Sarcoplasm |
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Nuclear envelope |
muscle |
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weakness |
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Emerin |
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Calf |
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Pathogenesis |
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hyper- |
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trophy |
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Duchenne-type MD |
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Proximal |
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Weakness of lid |
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muscle |
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closure (no |
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weakness |
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ptosis) |
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and atrophy |
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Myopathic |
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facies with weak- |
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girdle, dorsiflexion) |
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and winged scapula |
Weakness of mouth closure
Proximal |
Facioscapulohumeral MD |
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muscle |
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weakness |
Mild weakness |
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Calf |
Flexion contracture, |
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hyper- |
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focal atrophy |
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trophy |
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Limb girdle MD |
Cardiac arrhythmias, |
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Becker dystrophy |
respiratory insufficiency |
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Shortened |
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Achilles tendon |
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MD: Muscular dystrophy |
Emery-Dreifuss dystrophy |
Peripheral Nerve and Muscle
337
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Myopathies
The Myotonias (Table 69, p. 401)
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! Pathogenesis |
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Point mutations in ion channel genes cause |
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channel defects that render the muscle cell |
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membrane electrically unstable |
(Table 65, |
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p. 398), leading to involuntary muscle contrac- |
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tion. |
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! Symptoms and Signs |
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Muscle |
The transient, involuntary muscle contractions |
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are perceived as stiffness. Depolarizing muscle |
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relaxants used in surgery can trigger severe my- |
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otonia in susceptible patients. Acute, general- |
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ized myotonia can also be induced by tocolytic |
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Nerve |
agents such as fenoterol. |
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! Diagnosis |
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Peripheral |
Myotonia is diagnosed from the observation of |
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involuntary muscle contraction after voluntary |
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muscle contraction (action myotonia) or percus- |
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sion (percussion myotonia), along with the |
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characteristic EMG findings. Specific forms of |
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myotonia are diagnosed by their mode of inheri- |
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tance and clinical features, and molecular |
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genetic analysis. The serum creatine kinase con- |
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centration is usually not elevated, and there is |
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usually no muscle atrophy, except in myotonic |
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dystrophy. Muscle hypertrophy is present in |
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myotonia congenita. Myotonic cataract is found |
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in myotonic dystrophy and proximal myotonic |
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myopathy; slit-lamp examination is indicated in |
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patients with these disorders. |
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! Treatment |
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Membrane-stabilizing drugs such as mexiletine |
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alleviate myotonia; cardiac side effects may be |
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problematic, particularly in myotonic dystrophy. |
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Cold exposure should be avoided. |
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Episodic Paralyses (Table 69, p. 401) |
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! Pathogenesis |
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Hyperkalemic and normokalemic |
paralysis, |
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potassium-aggravated myotonia (PAM = myo- |
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tonia fluctuans), and paramyotonia congenita |
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are due to sodium channel dysfunction, while |
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hypokalemic paralysis is due to calcium channel |
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338 |
dysfunction. |
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! Symptoms and Signs
In hypokalemic and hyperkalemic myotonia, there are irregularly occurring episodes of flaccid paresis of variable duration and severity, with no symptoms in between. The anal and urethral sphincters are not affected. In paramyotonia congenita, muscle stiffness increases on exertion (paradoxical myotonia) and is followed by weakness. Cold exposure worsens the stiffness.
! Diagnosis
The diagnosis can usually be made from the personal and family history, abnormal serum potassium concentration, and molecular genetic findings (mutation of the gene for a membrane ion channel). If the diagnosis remains in question, provocative tests can be performed between attacks. The induction of paralytic attacks by administration of glucose and insulin indicates hypokalemic paralysis, while their induction by potassium administration and exercise (e. g. on a bicycle ergometer) indicates hyperkalemic paralysis. The diagnosis of paramyotonia congenita is based on the characteristic clinical features (paradoxical myotonia, exacerbation by cold exposure), autosomal dominant inheritance, and demonstration of the causative point mutation of the sodium channel gene.
! Treatment
Acute attacks. Milder episodes of weakness in hypokalemic disorders need no treatment, while more severe episodes can be treated with oral potassium administration. Milder episodes of weakness in hyperkalemic disorders also need no treatment; more severe episodes may require calcium gluconate i. v., or salbutamol by inhaler.
Prophylaxis. Hypokalemic paralysis: Low-salt, low-carbohydrate diet, avoidance of strenuous exercise; oral acetazolamide or spironolactone.
Hyperkalemic paralysis: high-carbohydrate diet; avoidance of strenuous exercise and cold; oral hydrochlorothiazide or acetazolamide.
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Myopathies
Unselective channel |
Sodium channel |
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Chloride channel |
Calcium channel |
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channel |
Cl- |
Na+ Ca2+ |
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Extracellular matrix |
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Cell membrane |
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K+ |
Cl- |
Intracellular matrix |
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Action myotonia (delayed |
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hand opening after grasping)
Ion channels for maintenance of transmembrane potential
Percussion myotonia (adduction of thumb on thenar percussion)
Myopathic facies, weakness of lid closure, atrophy of anterior neck muscles, myotonic cataract
Lingual percussion myotonia
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Predominantly |
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distal |
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muscular |
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Cold exposure |
atrophy |
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myotonia |
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(delayed eye |
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opening, facial |
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rigidity) |
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Myotonia congenita |
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(generalized muscular |
Paramyotonia congenita |
Myotonic dystrophy |
hypertrophy) |
Peripheral Nerve and Muscle
339
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Peripheral Nerve and Muscle
Myopathies
Congenital Myopathies
The typical pathological findings on muscle biopsy distinguish this group of disorders both from the congenital muscular dystrophies and from muscle changes secondary to peripheral neuropathy. Some congenital myopathies have distinctive clinical features. Proximal flaccid weakness is usually present at birth (floppy baby); skeletal deformities may also be seen (e. g., high palate, hip luxation, pes cavus, chest deformities). Many congenital myopathies progress slowly, causing little or no disability; the CK and EMG may be only mildly abnormal, or not at all. Some types can be diagnosed by genetic analysis (Table 70, p. 402).
Metabolic Myopathies
In most metabolic myopathies (Table 71, p. 402 f), exercise induces myalgia, weakness, and muscle cramps, and myoglobinuria. Progressive proximal weakness is seen in myopathy due to acid-maltase deficiency (glycogen storage disease type II), debrancher deficiency (glycogen storage disease type III), or primary myopathic carnitine deficiency.
!Ear (hearing loss)
!Heart (arrhythmia, heart failure)
!Gastrointestinal system (diarrhea, vomiting)
!Endocrine system (diabetes mellitus, hypothyroidism)
!ANS (impotence, sweating)
The diagnosis is based on the clinical features, laboratory tests (elevated lactate concentration at rest in serum, sometimes also in CSF, with sustained increase after exercise), muscle biopsy (ragged red fibers, sometimes with cy- tochrome-c oxidase deficiency), and molecular studies (mtDNA analysis of muscle, platelets, leukocytes). There is no etiological treatment for the mitochondrial myopathies at present; a lowfat, carbohydrate-rich diet is recommended in disorders with defective !-oxidation, and carnitine supplementation in those with systemic carnitine deficiency. Coenzyme Q10, vitamin K3, vitamin C, and/or thioctic acid supplements are recommended in disorders with impaired respiratory chain function.
Mitochondrial myopathies. Pyruvate and fatty acids are the most important substrates for mitochondrial ATP synthesis, which occurs by oxidative phosphorylation, a function of the respiratory chain enzymes (found on the inner mitochondrial membrane). !-oxidation occurs in the mitochondrial matrix. The respiratory chain enzymes are encoded by both mitochondrial and nuclear DNA (mtDNA, nDNA).
The mitochondrial myopathies are a heterogeneous group of disorders whose common feature is dysfunction of the respiratory chain, !- oxidation, or both. These disorders have varying clinical and biochemical features (Table 71, p. 402 f); their inheritance is either maternal or sporadic; non-heritable cases also occur through mtDNA mutations. These disorders may affect multiple organ systems, e. g.:
!Muscle (reduced endurance, pain, cramps, myoglobinuria)
!CNS (seizures, headache, behavioral abnor-
340malities)
!Eye (ptosis, external ophthalmoplegia, tapetoretinal degeneration)
Rohkamm, Color Atlas of Neurology © 2004 Thieme
All rights reserved. Usage subject to terms and conditions of license.
Myopathies
General- |
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muscle |
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Generalized mus- |
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weakness, |
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skeletal |
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cle weakness, |
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anom- |
Predom- |
skeletal anomalies |
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alies |
inantly |
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proximal |
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muscle |
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weakness |
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High palate |
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Nemaline |
Centronuclear |
Central core |
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myopathy |
myopathy |
disease |
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Congenital myopathies |
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Centrally located nuclei |
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myopathy; cross |
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Cardiac arrhythmias, |
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Optic neuropathy, |
section of muscle fiber) |
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cardiomyopathy |
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external ophthalmo- |
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Muscular weakness, |
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plegia, retinopathy |
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neuromy- |
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Hypacusis |
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Nuclear-coded |
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subunits of |
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ATP |
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drial sub- |
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mtDNA |
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chain defect |
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myoclonus, ataxia, |
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dementia, migraine, |
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infarction |
between nuclear and mitochondrial DNA |
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Mitochondrial |
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accumulation |
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(ragged red |
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fiber; cross |
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section of |
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Tapetoretinal |
Occipital |
muscle fiber) |
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degeneration |
infarcts (MELAS |
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(CPEO) |
syndrome, axial |
Paracrystalline mitochondrial |
Mitochondrial myopathies |
CT scan) |
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inclusions (electron microscopy) |
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Peripheral Nerve and Muscle
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Peripheral Nerve and Muscle
342
Myopathies
Myasthenic Syndromes
! Myasthenia Gravis (MG)
Pathogenesis. The exercise-induced weakness that typifies MG is due to impaired transmission at the neuromuscular junction, which is, in turn, due to an underlying molecular lesion affecting the nicotinic acetylcholine receptor (AChR) in the postsynaptic membrane of the muscle cell. Circulating IgG autoantibodies to this receptor impair its function, speed its breakdown, and induce complement-mediated damage to the muscle cell membrane. Recently the anti-MuSK (receptor tyrosine kinase) antibody has been detected in about half of patients who are seronegative for AChR antibodies. The thymus plays an important role in this autoimmune disorder (it is normally a site of maturation and removal of autoreactive T lymphocytes). MG is usually acquired late in life; there are also rare congenital and familial forms.
tor, such as pyridostigmine bromide; if the response is insufficient, corticosteroids or azathioprine can be added. Generalized MG is treated initially with AChE inhibitors and, if the response is insufficient, with corticosteroids, azathioprine, intravenous gammaglobulin, or plasmapheresis; once the patient’s condition has stabilized, thymectomy is performed. Further treatment depends on the degree of improvement achieved by these measures. The mortality of MG with optimal management is less than 1%. Most patients can lead a normal life but need lifelong immunosuppression. Specific measures are needed to manage respiratory crises, thymoma, and pregnancy in patients with MG, and for the treatment of neonatal, congenital, and hereditary forms of MG.
!Lambert–Eaton Myasthenic Syndrome (LEMS)
Symptoms and signs. MG is characterized by asymmetric weakness and fatigability of skeletal muscle that worsens on exertion and improves at rest. Weakness often appears first in the extraocular muscles and remains limited to them in some 15% of cases (ocular myasthenia), but progresses to other muscles in the rest (generalized myasthenia). The facial and pharyngeal muscles may be affected, resulting in a blank facial expression, dysarthria, difficulty in chewing and swallowing, poor muscular control of the head, and rhinorrhea. Respiratory weakness leads to impairment of coughing and an increased risk of aspiration. It may become difficult or impossible for the patient stand up, remain standing, or walk, and total disability may ensue. Myasthenia can be aggravated by certain medications (Table 72, p. 403), infections, emotional stress, electrolyte imbalances, hormonal changes, and bright light (eyes), and is often found in association with hyperthyroidism, thyroiditis, rheumatoid arthritis, and connective tissue disease. Myasthenic or cholinergic crises can be life-threatening (Table 73, p. 404). Diagnosis. The diagnosis is based on the characteristic history and clinical findings, supported by further tests that are listed in Table 74 (p. 404).
Treatment. Ocular MG is treated symptomatically with an acetylcholinesterase (AChE) inhibi-
LEMS is caused by autoantibodies directed mainly against voltage-gated calcium channels in the presynaptic terminal of the neuromuscular junction; diminished release of acetylcholine from the presynaptic terminal is the result. LEMS is often a paraneoplastic manifestation of bronchial carcinoma, sometimes appearing before the tumor becomes clinically evident. It is characterized by proximal (leg) weakness that improves transiently with exercise but worsens shortly afterward. There are also autonomic symptoms (dry mouth) and hyporeflexia. EMG reveals a diminished amplitude of the summated muscle action potential, which increases on high-frequency serial stimulation. The treatment is with 3,4-diaminopyridine (which increases acetylcholine release) and AChE inhibitors. Immune suppression and chemotherapy of the underlying malignancy can also improve LEMS.
Rohkamm, Color Atlas of Neurology © 2004 Thieme
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