Chapter 4: ALLERGY & IMMUNOLOGY

HAY FEVER, FOOD ALLERGIES, AND ALLERGIC RASHES

HAY FEVER/ALLERGIC RHINITIS

Hay fever due to pollen typically takes a few years to develop. Although some young children can start to show signs of allergic rhinitis, if a child younger than 3 years of age presents with rhinitis, consider other diagnoses.

• Ragweedfrequently causes Respiratory symptoms along with the usual sneezing, allergic conjunctivitis, rhinitis, and tearing of hay fever.
• Treatment options include intranasal steroids (first-line therapy for symptoms), oral antihistamines, and intranasal antihistamines.

CHRONIC RHINITIS

Chronic rhinitis is diagnosed once symptoms have been present for at least four weeks consecutively. The differential for chronic rhinitis includes HAY FEVER, SINUSITIS, CYSTIC FIBROSIS, FOREIGN BODY, a nasal POLYP, and VASOMOTOR RHINITIS.

VASOMOTOR RHINITIS

Triggers for vasomotor rhinitis may include emotions, cold wind, change in temperature (or humidity), and pollution. Typical environmental allergens are NOT triggers.

SKIN TESTING

SKIN TESTING = AEROALLERGEN TESTING

• FALSE negatives can occur when patients are on antihistamines or antidepressants!
• NEGATIVE PREDICTIVE VALUE: NPV of skin testing for foods or inhalants is excellent.
• POSITIVE PREDICTIVE VALUE: PPV is good for inhalants but not good for foods.

PEARL/SHORTCUT: Skin-testing results are considered fairly reliable for airborne substances (e.g. pollen, pet dander, and dust mites). Skin testing can be helpful in diagnosing food allergies when an OFC is not feasible for certain clinical settings because of the concern for anaphylaxis, but the rate of false positives is high.

PEARL: Oral food challenge (OFC) under the supervision of a clinician is the gold standard for diagnosing a food allergy given the potential for false positive skin testing and RAST results. Initially, the potential food allergen is eliminated from the diet (called an “elimination diet”). Chronic symptoms may improve and a provisional food allergy diagnosis is given until an OFC can be done to confirm the diagnosis where possible.

IMMUNOTHERAPY

About 50% of patients with hay fever respond to immunotherapy. There’s a 0.5% chance (1 in 200) of having a severe reaction during therapy. If it happens, it will usually occur within 30 minutes, and will usually occur during peak pollen seasons or within the first year of immunotherapy (the rapid build-up phase).

PEARL: Contraindications for immunotherapy include poorly controlled asthma, beta blocker use, and history of repeated episodes of anaphylaxis with allergy shots.