allergy

the genetic tendency to develop a hypersensitivity reaction to common environmental substances (allergens)

• High degree of heritability & concordance
• among twins

• –Allergic
• rhinitis > urticaria > asthma

a + GHx ((esp if both parent are atopic)

◦Seasonal pollens (grass pollens, ragweed)

◦Outdoor molds (airborne fungi)

◦Indoor allergens (indoor fungi, animal dander, dust mites, insects)

◦Sneezing, rhinorrhea (clear secretions), nasal congestion, itching in the nose & palate

• ◦Less common signs: conjunctivitis
• (allergen must be blown into the eyes), fatigue, arthralgia, myalgia, cognitive
• changes (esp in children) - these are mostly cytokine-mediated effects

◦Other: obstruction of sinus ostia causing acute (bacterial) sinusitis

• ◦Avoidance of the allergen is the best
• intervention

◦First-line therapy: antihistamines - first generation formulas reduce motor skills, second generation compounds are better

• ◦Immune therapy: anti-IgE (omalizumab) -
• effective but $$

pruritic (itchy), erythematous (red) & blanching (loose color with pressure) skin papules (slightly raised bumps!) 

◦Shape: round or oval with pale raised centers (wheals)

◦Size: varies from several millimeters to a few centimeters

• ◦immediate release of histamine, leukotrienes
• & PGs from mast cells (vasodilitation, leakage of plasma from venules)

involves non-pitting edema of lips, tongue, eyelids, hands, feet or genitalia 

◦May involve the oropharynx & larynx

◦No report of itching but may feel burning or pressure (stretching)

• ◦Swelling involves a delayed reaction caused by inflammatory cytokines released in
• subcutaneous or submucosal tissues

◦Food – requires chronic exposure (i.e., wheat)

◦Physical – triggered by scratching, exercise, exposure of skin to heat, ice, vibration, pressure, UV radiation, chronic infections (sinusitis, dental abscess, H. pylori)

◦Immune-mediated – during flares of autoimmune diseases such as rheumatoid arthritis, Hashimoto’s thyroiditis

◦Complement-mediated - Hereditary Angioneurotic Edema

5-30 minutes after ingesting a drug or food or insect bite, but may also be idiopathic

Treatment

• ◦Acute cases are self-limited; antihistamines
• can prevent recurrent attacks

• ◦Antileukotriene
• medications or corticosteroids may become
• necessary for severe or chronic cases

Treatment

• ◦Acute cases are self-limited; antihistamines
• can prevent recurrent attacks

• ◦Antileukotriene medications or corticosteroids may become
• necessary for severe or chronic cases

• ◦An autosomal dominant
• trait

◦Involves a deficiency of C1 esterase inhibitor - a regulatory protein that controls and limits complement activation, fibrinolysis & bradykinin production – it is this latter process that causes capillary leakage and edema

◦Mild attacks may begin in infancy but become severe at puberty

• ◦Swelling is spontaneous or precipitated
• by pressure, trauma, stress

no tx

◦Epinephrine is only modestly effective

• ◦Other approaches may include
• antihistamines, attenuated androgens, transfusion with FFP

• Acute attacks may require nasotracheal
• intubation

Immediate and life-threatening  hypersensitivity reaction

• Allergy mediators are found in multiple organs
• –Skin: urticaria, angioedema, flushing
• –Respiratory:laryngeal edema, bronchospasm
• –CV:hypotension, arrhythmia, 
• –GI:nausea, vomiting, gastrointestinal spasms

• Most common allergens are drugs, insect venoms, foods, radiocontrast media & latex
• ◦Allergen exposure must lead to sensitization before an immediate hypersensitivity can occur