Panniculitis with late onset enthesitis-related arthritis: a case report

BACKGROUND: Panniculitis, a type of inflammation of subcutaneous fat, is a relatively uncommon condition that usually presents as inflammatory nodules or plaques, with various proposed etiologic factors. The association between panniculitis and enthesitis-related arthritis has not been described previously. CASE PRESENTATION: Herein, we describe a case of a 11-year-old girl who presented with recurrent fever and painful subcutaneous nodules on her extremities and buttocks. Histological examination of the skin biopsy specimen revealed lobular panniculitis. Despite the use of prednisone and mycophenolate mofetil for several months, the patient experienced a relapse of skin lesions and additional symptoms of peripheral joint swelling and inflammatory lumbar pain. She was diagnosed with enthesitis-related arthritis after confirmation by imaging. The panniculitis demonstrated a sustained response when a tumor necrosis factor alpha inhibitor was used for enthesitis-related arthritis. At 2-year follow-up, her skin lesions and arthritis remained stable. CONCLUSIONS: Although rare, panniculitis can be considered an unusual extra-articular manifestation of enthesitis-related arthritis based on clinical and pathological insights.