Recurrent Erythema Multiforme Definition
Recurrent erythema multiforme (EM) is defined as experiencing 6 or more episodes per year on average, based on the largest clinical case series. 1, 2
Established Clinical Criteria
The mean number of attacks in documented recurrent EM cases is 6 episodes per year (range 2-24 episodes annually), according to the largest British case series of 65 patients with recurrent EM 2
A subsequent Mayo Clinic series of 48 patients with recurrent EM confirmed similar patterns, with patients experiencing multiple episodes annually over a mean disease duration of 6 years 1
Any patient experiencing 2 or more episodes per year warrants classification as recurrent EM and should trigger investigation for underlying causes and consideration of prophylactic therapy 2
Disease Chronicity and Natural History
Recurrent EM demonstrates substantial chronicity, with a mean disease duration of 9.5 years (range 2-36 years) in the British cohort, reflecting the persistent nature of this condition 2
The Mayo Clinic series showed a mean duration of 6 years, indicating that once established, recurrent EM tends to persist for extended periods 1
The frequency of episodes does not necessarily decrease over time without intervention, emphasizing the importance of identifying triggers and initiating appropriate prophylactic treatment 2
Clinical Implications of Episode Frequency
Patients with higher episode frequencies (approaching 24 episodes per year, or roughly twice monthly) represent the most severe end of the spectrum and typically require aggressive prophylactic therapy 2
Oral mucous membrane involvement occurs in 63-69% of recurrent EM cases, which significantly impacts quality of life and may necessitate more intensive management regardless of episode frequency 1, 2
Herpes simplex virus (HSV) is identified as the precipitating factor in 23-71% of recurrent EM cases, with the variation reflecting differences in diagnostic rigor and patient populations 1, 2
Practical Clinical Threshold
While 6 episodes per year represents the mean in documented case series, any patient with 3-4 or more episodes annually should be evaluated for recurrent EM and considered for prophylactic antiviral therapy if HSV-associated 2
The lower threshold of 2 episodes per year in the British series suggests that even biannual recurrences warrant attention, particularly if episodes are severe or involve mucosal surfaces 2