A tick bite from the Lone Star tick can trigger a severe allergy to red meat.
This specific allergy is related to a carbohydrate called alpha-gal found in red meat. So do patients become allergic to themselves? No! Interestingly, the alpha-gal molecule is found in all mammals except apes, humans, and Old World monkeys.
12.1 Hypersensitivity Reactions
Anaphylaxis: involvement of respiratory (respiratory compromiseb) and/or circulatory system (vasodilatory shock)
Occurs 1 or more weeks after allergen exposure, but can also manifest much later
Presentation depends on the target of autoantibody:
For severe, persistent disease, treatment options include steroids and other immunosuppressants.
Primary damage is from immune complexes (antigen-antibody complexes).
For severe persistent disease, can use steroids, azathioprine, methotrexate, mycophenolate mofetil, etc.
Delayed (>48 hours after allergen exposure; sometimes may take days or weeks to develop)
Poison ivy, Crohn’s disease, multiple sclerosis, morbilliform drug eruption, Stevens-Johnson syndrome, toxic epidermal necrolysis, DRESS syndrome, etc.
aCan be caused by anything: drugs, infection, foods, latex, bee sting, etc. Note that in a lot of cases history of sensitization might not be present.
Abbreviations: DRESS, drug reaction with eosinophilia and systemic symptoms; IVIG, intravenous immunoglobulin.
12.1.1 Highly Allergenic Drugs
Theoretically, almost any drug can cause hypersensitivity reaction, but the most notorious ones are the following:
Most of the drugs that fall into this category have the word “sulf” in them:
• Sulfamethoxazole (antibiotic)
• Sulfasalazine (antiinflammatory drug)
• Sulfinpyrazone (uricosuric drug)
Additionally, drugs which have the suffix “ide” (e.g., chlorpropamide —antidiabetic drug, diuretics—furosemide, acetazolamide, hydrochlorothiazide, bumetanide) have some sulfa component, but most are well tolerated and have very low cross-reactivity with other sulfonamides.
Penicillins and cephalosporins
Antiseizure medication (phenytoin, lamotrigine, valproic acid, carbamazepine, phenobarbital)
These drugs can cause all four types of hypersensitivity (urticaria, anaphylaxis, autoimmune hemolytic anemia, serum sickness, allergic interstitial nephritis, maculopapular rash, toxic epidermal necrolysis, Stevens-Johnson syndrome, etc.). They will be called “highly allergenic drugs” for the purpose of this book.
These drugs are commonly implicated but any medication has the potential to cause allergic reaction in a genetically susceptible individual
Example: Allopurinol, various ACE inhibitors and proton-pump inhibitors are implicated in inciting all types of allergic reaction , but is less common than the highly allergenic drugs.
1. With diagnosis of otitis media, patient was started on amoxicillin more than a week ago. Patient now presents with new onset fever, rash, joint pain, and lymphadenopathy. ANA is negative. What is the likely dx?
An adult patient has hypotension and shortness of breath after a bee sting. Patient reports no hx of bee sting in the past. Exam reveals diffuse swelling of eyelids, lips, and bilateral extensive wheezing. He then develops hypotension.
12.1.2 Urticaria (Hives)
Pathophysiology: Edema of epidermis
Food (e.g., peanuts, shellfish, eggs), medications, insect bites, latex, infection, etc.
Physical urticariaa, or underlying systemic disorder (autoimmune, vasculitis, malignancy, etc.)
Antihistamines (H1– blockers)b
Steroids can be used in significant cases not responding to above regimen.
In severe cases not responding to above regimen, use omalizumab (anti-IgE antibody). If not responding, use anti-inflammatory agents such as dapsone, sulfasalazine, hydroxychloroquine, or in more severe cases, immunosuppressives such as tacrolimus.
a Physical urticaria: Mast-cell degranulation due to physical factors such as exercise, sunlight, hot or cold temperatures, etc.
Antihistamines (H1– blockers) Side effects
Definition: Edema of deep dermis, subcutaneous and/or submucosal tissue due to increased vascular permeability.
3Angioedema of lower lip Source: Localized Edema. In: Siegenthaler W, ed. Siegenthaler’s Differential Diagnosis in Internal Medicine: From Symptom to Diagnosis. 1st ed. Thieme; 2007.
Respiratory distress and arresta
Colicky abdominal pain
aIn a patient presenting with angioedema, the first step is to assess airway. If there is impending airway compromise, NSIM is intubation.
Histamine-mediated angioedema or mast-cell-mediated angioedema (allergic reaction)
Etiology: Most commonly due to allergic triggers such as foods (e.g., peanuts, shellfish, eggs), pollen, medications (highly allergenic drugs), insect bites, rubber latex, contrast media, etc. This can also be due to physical factors such as exercise, sunlight, hot or cold temperatures, etc.
1. Bradykinin-mediated angioedema due to ACE-i: this is the most common form of bradykinin-mediated angioedema (it can occur any time after initiation)b
2. Bradykinin-mediated angioedema not related to ACE-i: This can be hereditary or acquired
Pathophysiology: Decreased activity of Cl inhibitor → increased C1 activity→increased activation and consumption of complement proteins (low C3, C4) →increased production of bradykinin and other edema mediators.
aAfter an anaphylaxis episode, the serum tryptase level increases (tryptase is a unique mast cell protein). This is useful for diagnosis in atypical cases, but the level needs to be drawn within few hours of symptom onset, as it rapidly falls to normal levels within few hours of the episode.
b Angiotensin-receptor blockers (ARBs), unlike ACE-i, do not decrease bradykinin metabolism. They act only by blocking angiotensin receptors. Hence ARBs can be given to patient with ACE-i-related angioedema.
cIf angioedema is idiopathic and does not fit into the above classification, treat as histamine-mediated angioedema.
dFor example, patient has anaphylaxis due to bee sting, but he is a bee farmer and would like to continue to work. Prior to desensitization any adrenergic blocking agents (such as B-blockers) must be stopped, because epinephrine might be required if the patient develops an anaphylactic reaction during the procedure.
Abbreviations: ACE-i, angiotensin-converting enzyme inhibitor; CLL, chronic lymphocytic leukemia; SLE, systemic lupus erythematosus.