When a bruise is not a bruise: chronic recurrent erythema nodosum of unidentified cause in a young woman

Abstract

Introduction: erythema nodosum is the most common form of panniculitis. Although typically self-limiting, it can follow a chronic and recurrent course with no identifiable cause, posing both diagnostic and therapeutic challenges—particularly in settings where access to specialized diagnostic studies is limited.

Case presentation: a 25-year-old woman, who is a smoker and has iron-deficiency anemia, presented with a fever of up to 39°C lasting 9–10 days, accompanied by the successive appearance of painful, warm, erythematoviolaceous lesions—resembling ecchymoses—on both lower extremities. A superficial thrombotic event was initially suspected, and acetylsalicylic acid was prescribed. The patient was admitted for an etiological investigation. Findings included hypochromic anemia, mild leukopenia, an erythrocyte sedimentation rate (ESR) of 18 mm/h, and proteinuria; a chest X-ray was normal, and serological tests for syphilis and human immunodeficiency virus (HIV) were negative. As there was no response to non-steroidal anti-inflammatory drugs (NSAIDs), the patient was treated with prednisone (0.5 mg/kg/day), with a gradual taper. Over approximately 11 months of follow-up, she experienced recurrent, migratory outbreaks, with no sustained response to steroids and no identifiable underlying cause.

Conclusions: erythema nodosum can be chronic and recurrent without an identifiable cause, showing only partial or transient responses to anti-inflammatory drugs and steroids. This diagnosis should be considered when painful, bruise-like nodules appear on the lower extremities. In resource-limited settings, a meticulous clinical assessment and basic diagnostic tests can guide the diagnosis, while long-term follow-up allows for the ongoing re-evaluation of potential underlying causes.