Полезные материалы за все 6 курсов / Учебники, методички, pdf / Kaplan Pediatrics USMLE 2CK 2021

Chapter 9 λ Allergy and Asthma

Urticaria and Angioedema

Causes:

•Acute, IgE-mediated (duration <6 weeks)

–Activation of mast cells in skin

–Systemically absorbed allergen: food, drugs, stinging venoms; with allergy, penetrates skin → hives (urticaria)

•Non IgE-mediated, but stimulation of mast cells

–Radiocontrast agents

–Viral agents (especially EBV, hepatitis B)

–Opiates, NSAIDs

•Physical urticarias; environmental factors—temperature, pressure, stroking, vibration, light

•Hereditary angioedema

–Autosomal dominant

–C1 esterase-inhibitor deficiency

–Recurrent episodes of nonpitting edema

•Diagnosis mainly clinical; skin tests, IgE-specific allergens (blood)

•Treatment

–Most respond to avoidance of trigger and oral antihistamine

–Severe—epinephrine, short-burst corticosteroids

–If H1 antagonist alone does not work, H1 plus H2 antagonists are effective; consider steroids

–For chronic refractory angioedema/urticaria → IVIg or plasmapheresis

Anaphylaxis

•Sudden release of active mediators with cutaneous, respiratory, cardiovascular, gastrointestinal symptoms

•Most common reasons

–In hospital—latex, antibiotics, IVIg (intravenous immunoglobulin), radiocontrast agents

–Out of hospital—food (most common is peanuts), insect sting, oral medications, idiopathic

•Presentation—reactions from ingested allergens are delayed (minutes to 2 hours); with injected allergen, reaction is immediate (more gastrointestinal symptoms)

•Treatment

–What the patient should do immediately:

°Injectable epinephrine

°Oral liquid diphenhydramine

°Transport to ER

–Medical:

°Oxygen and airway management

°Epinephrine IM (IV for severe hypotension); intravenous fluid expansion; H1 antagonist; corticosteroids; nebulized, short-acting beta-2 agonist (with respiratory symptoms); H2 antagonist (if oral allergen)

Chapter 9 λ Allergy and Asthma

•Treatment

–Identify and eliminate causative factors

–Cutaneous hydration

°Dry skin, especially in winter (xerosis)

°Lukewarm soaking baths followed by application of occlusive emollient (hydrophilic ointments)

–Topical corticosteroids

°Seven classes—the higher potency classes are not to be used on face or intertriginous areas and only for short periods

°Goal—emollients and low-potency steroids for maintenance

–Topical immunomodulators; tacrolimus (calcineurin inhibitor):

°Inhibits activation of key cells

°Ointment safe and effective

°Safe on face

°Can use as young as age 2 years

–Tar preparations

–Phototherapy—UV light

–Systemic: antihistamines (sedating at night; for pruritus); glucocorticoids; cyclosporine (refractory to all other treatment); interferon (if all else fails)

–Treat with antibiotics for bacterial superinfection

•Complications

–Secondary bacterial infection, especially S. aureus; increased incidence of

T. rubrum, M. furfur

–Recurrent viral skin infections—Kaposi varicelliform eruption (eczema herpeticum) most common

–Warts/molluscum contagiosum

ASTHMA

A 6-year-old boy presents to his physician with end-expiratory wheezing scattered throughout the lung fields. He is noted to have nasal flaring, tachypnea, and intercostal retractions. These symptoms are triggered by changes in the weather. He has a family history of asthma and atopic dermatitis. He has never been intubated or admitted to the pediatric ICU. His last hospitalization for asthma was 6 months ago. He takes medication for asthma only when he starts to wheeze.

•Etiology/pathophysiology

–Chronic inflammation of airways with episodic at least partially reversible airflow obstruction

°Genetic and environmental factors: concomitant allergies (perennial in most), induced by common viral agents, tobacco smoke; cold, dry air; strong odors

°Most with onset age <6 years; most resolve by late childhood

°Two main patterns:

Early childhood triggered primarily by common viral infections

Chronic asthma associated with allergies (often into adulthood; atopic)

Chapter 9 λ Allergy and Asthma

USMLE Step 2 CK λ Pediatrics

90

Immune-Mediated Disease 10

Chapter Title

Learning Objectives

Explain information related to evaluation of suspected immune deficiency

Categorize specific defects of immune deficiency

Chapter 10 λ Immune-Mediated Disease

SPECIFIC DEFECTS

Defects of Antibody Production

X-linked (Bruton) agammaglobulinemia

X-linked (Bruton) agammaglobulinemia (XLA) is a profound defect in B-cell development which leads to an absence of circulating B cells and thus leads to severe hypogammaglobulinemia with small-to-absent tonsils and no palpable lymph nodes.

•Genetics: >500 known mutations of the Btk gene (Bruton tyrosine kinase), which is necessary for pre-B-cell expansion and maturation; long arm of X-chromosome

•Clinical findings: boys with pyogenic sinopulmonary infections

•Diagnosis: clinical presentation + lymphoid hypoplasia on exam; all immunoglobulins severely depressed; flow cytometry shows absence of circulating B-cells; gene sequencing for specific mutation

•Treatment: appropriate use of antibiotics + regular monthly IVIG

NOTE: The only 2 B-cell defects for which stem cell transplantation is recommended are CD40 ligand defect (extremely rare; one of the known mutations on the X-chromosome for hyper-IGM syndrome) and X-linked lymphoproliferative disease.

Common variable immunodeficiency

Common Variable Immunodeficiency (CVID) is hypogammaglobulinemia with phenotypically normal B-cells; blood B-lymphocytes do not differentiate into IG-producing cells

•Genetics: majority have no identified molecular diagnosis, so are sporadic; may have a common genetic basis with selective IgA deficiency (occurs in families together and some later with IgA may develop CVID)

•Clinical findings: boy or girl (equal sex distribution) with later onset infections, less severe; clinically similar to XLA, but rare echovirus meningoencephalitis

•Diagnosis: clinical presentation + serum IG and antibody deficiencies as profound or less than in XLA; normal sized lymphoid tissue; later autoimmune disease and malignancy (lymphoma)

•Treatment: need to be screened for anti-IgA antibodies (as in selective IgA deficiency)→ if present, therapy consists of the one IG preparation available that contains no IgA.

Selective IgA deficiency

Selective IgA deficiency is the most common immunodeficiency. It is caused by the absence or near absence of serum and secretory IgA with phenotypically normal B-cells

•Genetics: basic defect is unknown; boys and girls and familial pattern suggests autosomal dominant with variable expression; also seen in families with CVID (as above); both may be triggered by environmental factors

•Clinical findings: same bacteria as others with most infections in respiratory, GI and urogenital tracts; giardiasis is common