What investigations should be considered in a patient with recurrent episodes of erythema multiforme?

Investigations to consider in a patient with recurrent erythema multiforme include:

• Testing for herpes simplex virus (HSV) infection, as recurrent erythema multiforme is often associated with HSV reactivation. Referral to a specialist for consideration of long-term suppressive antiviral therapy may be appropriate if HSV is implicated.
• Assessment for possible drug allergy, including a detailed drug history and consideration of specialist drug allergy testing if a drug cause is suspected, especially if episodes are severe or systemic features are present.
• HIV testing if lesions are extensive or if there is clinical suspicion, given that immunosuppression can influence recurrent herpetic infections.
• Allergy-focused clinical history and possibly skin prick or specific IgE blood tests if a food allergy or other allergic trigger is suspected, particularly in children or young people.

These investigations help identify underlying triggers such as HSV infection or drug allergy, which are common causes of recurrent erythema multiforme, and guide management including specialist referral if needed.

References: NICE CKS, NICE CKS, NICE CKS, NICE CG183, NICE CG116