2. Assessment
The physical exam revealed a well-nourished, well-developed, middle-aged male in no acute distress. His vital signs were all within normal limits. A head and neck exam included a normocephalic head, with no lesions present. Facial erythema was noted across the malar region. Pupils were equally round and reactive to light and accommodation, and extra-ocular movements were intact. There was bilateral periorbital swelling noted along with swelling of both the upper and lower eyelids. Conjunctivas were normal, and no drainage was noted. Nasal mucosa was normal. The oral cavity showed no edema or erythema of palate or tongue. Inspection and palpation of the neck showed no masses, tenderness, or lymphadenopathy. Lung sounds were clear to auscultation in all fields, and heart sounds were of a normal rate and rhythm. Bilateral forearms had a raised erythematous rash present.
3. Labs
A radioallergosorbent test (RAST) of immunoglobulin E (IgE) was performed to rule out new onset of allergies to foods that would be common in most adult diets. RAST was conducted for milk, wheat, corn, peanut, soybean, shrimp, tomato, orange, chicken, walnut, egg, rice, and beef. All were within normal limits (reference <0.35 kU/L), with the exceptions of walnut (0.16 kU/L), beef (1.08 kU/L), and shrimp (0.59 kU/L). A C1 esterase inhibitor level was drawn to check for hereditary angioedema type 1. It was found to be within normal limits at 28 mg/dL (reference range 21-39 mg/dL). Galactose-alpha-1, 3-galactose IgE (alpha-gal) was drawn to check for sensitivity to the oligosaccharide that has been linked to adult onset of mammalian meat allergy. It was found to be elevated at 1.71 kU/L (reference <0.35 kU/L).
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4. Diagnosis
Based on the patient’s presentation and physical exam, the initial diagnosis of urticaria and angioedema was made. Differential diagnosis included contact dermatitis, acute inhalant allergen flare, new onset of food allergy, and various autoimmune disorders. A diagnosis of alpha-gal allergy was made based on the patient’s food intake the day of the reaction, his history and likely exposure to tick bites while hunting, and lab work showing an elevation of both beef and alpha-gal-specific IgE.
5. Treatment
Initial treatment for the urticaria and angioedema included 6 mg of betamethasone administered via intramuscular injection. The patient was advised to continue 180 mg of daily fexofenadine, and the H2 blocker famotidine was added for twice-daily use for 1 week. The patient was prescribed a 0.3-mg epinephrine pen injector, and the signs and symptoms of anaphylaxis along with proper injection technique of the pen injector were reviewed. Once the results of the patient’s labs returned and a diagnosis of alpha-gal allergy was made, the patient was informed of the result and educated about alpha-gal allergy. He was encouraged to avoid all mammalian meat ingestion, including pork, lamb, beef, and game and to try to prevent future tick bites. He was advised to return after 6 months to repeat testing for IgE specific to alpha-gal, beef, and pork.
6. Discussion
Alpha-gal is an oligosaccharide found in all mammals with the exception of primates.1 Alpha-gal allergy is commonly referred to as alpha-gal allergy. In 2005, patients experiencing reactions to the therapeutic antibody cetuximab were found to have IgE antibodies to the drug despite never receiving it. The IgE was specific to alpha-gal, which was found to be present in the structure of the drug.2 A connection was then made between cases of cetuximab anaphylaxis and areas of the United States where Rocky Mountain spotted fever is found.3 Rocky Mountain spotted fever is a known tick-borne illness, which led researchers to think that the development of alpha-gal-specific IgE may be associated with exposure to tick bites.2 It is thought that human beings who have developed antibodies to this carbohydrate have done so after being bitten by a tick.
