Cutaneous drug reactions

A patient popped in a few weeks ago with a diffuse maculopapular rash following recent administration of a new medication. The rash had started on the trunk and was spreading to the limbs. That, and the fact that we need to prep this scenario for our finals has resulted in this blog post.

Source: Best Practice (a subscription is necessary), Harrison's Practice

Spectrum of drug induced cutaneous reactions. Other conditions to consider include fixed drug eruptions and DRESS* (drug reaction with eosinophils and systemic symptoms).

.

·       *DRESS presents with 

• maculopapular rash
• fever >38C
• abN LFTs
• evidence of other organ involvement
• lymphadenopathy in at least 2 sites,
• abN FBC 

 If you're not certain it's a drug-induced reaction, ask for a dermatology consult. They arethe best at diagnosing rashes. Other causes of rash includes: SLE, psoriasis, meningococaemia (non-blanching), viral exanthems, et al.

History

• Recent drug exposure and timing
• Previous exposure and reaction to this drug
• Presence and variability of skin lesions
• Presence of pain or pruritis
• Allergies

Examination

• Signs and symptoms of anaphylaxis (rhinitis, conjunctivitis, urticaria, N,V, abdo pain, angioedema, asthma, pulm edema, tachycardia, hypotension, et al)
• Signs of SJS (involvement of mucous membranes of eyes and mouth)
• Signs of TEN: widespread desquamation

Investigations

• Bloods
• Drug concentrations
• FBC & differential (raised eosinophils due to degranulation of mast cells)
• Serum complement & anti-single stranded DNA (lupus like syndrome)
• Skin prick tests and serum tryptase
• Tissue biopsy

Management

• Withdraw medication

• If anaphylaxis
• Adenaline and supportive care
• Consider oral corticosteroids & IV IG
• If SJS or TEN
• Topical dressings
• Supportive management
• Similar to burns management
• For urticaria
• Antihistamine and H2 antagonist
• TCA
• For asthma
• Bronchodilators
• O2
• Long term care
• Avoidance of offending drug
• Education on use of epipen (action plan) & MedicAlert  bracelet
• Drug desensitization if continued drug use is necessary
• Report reaction to local pharmacy

There is probably a whole lot more you can do but this is the gist of what I will be remembering for my exams!

**Read the disclaimer**