In our Morning Report at WCH, we discussed the major cutaneous manifestations of adverse drug reactions, with a focus on type IV hypersensitivity.
Learning Points:
- Differential diagnosis of pruritus
- Major cutaneous morphologies of drug reactions
- Differential diagnosis of morbilliform exanthems
- Differential diagnosis of erythroderma
- Gel & Coombs classification schema
- Management of morbilliform drug eruptions
Differential diagnosis of pruritus:
Major Cutaneous Morphologies of Drug Reactions:
- Morbilliform-also termed “maculopapular”
- Urticarial
- Erythroderma
Morbilliform Eruptions:
- three major “categories” of causes of maculopapular/morbilliform eruptions
- These will AID your diagnostic ability:
Erythroderma Differential Diagnosis:
Gel & Coombs Classification of Drug Hypersensitivity
Examples:
Type I: B lactam-induced anaphylaxis
Type II: Heparin-induced thrombocytopenia
Type III: Serum sickness
Type IV: Morbilliform eruptions, DRESS (Drug rash with eosinophillia and systemic symptoms), AGEP (acute generalized exanthematous pustolosis), SJS/TEN
Management Pearls for Morbilliform Drug Eruptions/Type IV hypersensitivity:
- Culprit drug should be stopped
- There is NO ROLE for premedication or desensitization subsequently
- desensitization is ONLY an option for Type I hypersensitivity
- Be vigilant for evolution to more severe Type IV hypersensitivity reactions like DRESS, AGEP, and SJS/TEN because morbilliform exanthems may herald these more severe forms.
- Worrisome features suggestive of evolution may include:
- Fever
- Mucositis
- Rash progression to erythroderma
- Blistering or skin tenderness
- Worrisome features suggestive of evolution may include:
- Symptomatic treatment is indicated for pruritus, though may not be particularly effective due to the underlying physiologic mechanism
- There is no role for steroids in uncomplicated, mild, morbilliform eruptions
- If indicated, basic bloodwork would include a CBC (eosinophilia), and liver/renal indices to assess for systemic organ involvement
- There is NO role for skin prick testing to evaluate culprit drugs in relation to type IV hypersensitivity
- Skin prick testing is ONLY for IgE-mediated reactions
- Patch testing to the culprit drug is SOMETIMES used, though of limited utility
- Many drugs have “sulfa” components, including antimicrobial and non-antimicrobial agents.
- There is little evidence of cross-reactivity between sulfa-containing antimicrobials and sulfa-containing non-antimicrobials (though not impossible)
Further Reading:
- Warrington, R and Silviu-Dan, F. Drug Allergy. Allergy, Asthma & Clinical Immunology 2011, 7(Suppl 1):S10. http://www.aacijournal.com/content/7/S1/S10