Erythema Multiforme: Triggers and Differential

Overview / Definition Erythema multiforme (EM) is a hypersensitivity reaction that primarily affects the skin and mucous membranes, presenting with distinctive skin lesions and a range of associated symptoms. The condition is classified into two main forms: erythema multiforme minor, which is typically self-limiting and associated with herpes simplex virus (HSV) infections, and erythema multiforme major, which can involve systemic symptoms and is often related to drug reactions. Epidemiology EM is relatively uncommon, with an estimated incidence of 1-2 cases per 1,000,000 people annually. The condition can occur at any age but is most prevalent in young adults, particularly those aged 20-40 years. Male patients are affected more frequently than females, and the incidence of EM is notably higher in individuals with a history of recurrent herpes simplex infections. Pathophysiology / Mechanism The pathophysiology of erythema multiforme involves an immune-mediated response, often triggered by infections or medications. The classic target lesions result from the interaction between the epidermis and the dermal vasculature, leading to a combination of keratinocyte apoptosis and dermal inflammation. The following factors can initiate this process: Infectious triggers: Most commonly associated with HSV infections, also linked to Mycoplasma pneumoniae, and other viral infections. Drug-related triggers: Commonly implicated medications include sulfonamides, penicillins, and non-steroidal anti-inflammatory drugs (NSAIDs). Miscellaneous triggers: Include vaccinations, systemic diseases such as lupus erythematosus, and physical stimuli. Clinical Presentation Patients with EM typically present with a characteristic triad of symptoms: Target lesions: Well-defined, concentric rings that can appear on the trunk and extremities. Mucosal involvement: In erythema multiforme major, patients may present with lesions on the oral mucosa, genitalia, or conjunctiva. Prodromal symptoms: These