- A 38-year-old woman presented with painful lesions on both shins that first appeared a few days earlier. Physical examination revealed multiple red tender nodules on both legs. The patient had been treated with nonsteroidal anti-inflammatory drugs for having a few months without any improvement. The patient was referred to a dermatologist and a rheumatologist, who confirmed our diagnosis of chronic erythema nodosum (EN). She returned to the clinic 3 months later complaining of having numbness in the soles of her feet for a few weeks. Her serum vitamin B12 level was 118 pg/mL (normal range 135 to 911). After 4 weeks of twice weekly injections of vitamin B12 at a dose of 1000 mcg, there was a clear alleviation of the numbness, and the EN completely resolved without evidence of recurrence on follow-up. Because it seems that vitamin B12 caused resolution of EN in this case, we recommend that physicians consider testing for vitamin B12 deficiency in patients with EN.