Erythema Nodosum in Hidradenitis Suppurativa: A Case Series

Hidradenitis suppurativa (HS) is a chronic inflammatory condition linked to dermatologic and multisystem comorbidities, including pyoderma gangrenosum, arthritis, inflammatory bowel disease, and Behcet's disease. While associations with immunological and inflammatory conditions are less frequently reported, erythema nodosum (EN) has an adjusted odds ratio of 8.36 in HS patients. Erythema nodosum, a type IV hypersensitivity reaction, is a panniculitis characterized by acute inflammation triggered by factors such as dimorphic fungal infections, tuberculosis, sarcoidosis, and medications like oral contraceptives and antibiotics. A link between EN and tumor necrosis factor alpha (TNF-alpha) inhibitors is suggested by case reports. Adalimumab is used in the treatment of moderate-to-severe HS, and EN in these patients could be related to the drug or the disease. This case series describes cases of EN in patients with HS and the relationship with adalimumab exposure.