Erythema nodosum-like lesions associated with giant cell arteritis diagnosed by ultrasonography.

Giant cell arteritis (GCA) is a large-vessel vasculitis that primarily affects older adults and rarely presents with cutaneous lesions. We describe a woman in her 70s who developed tender erythema nodosum (EN)-like nodules on both lower legs together with headache. Histopathology showed septal panniculitis composed of lymphohistiocytic infiltrates and multinucleated giant cells without vasculitis or fibrinoid necrosis. Ultrasonography of the temporal artery revealed irregular wall thickening and tortuosity, findings that suggested a hypoechoic 'halo sign' typical of active arteritis. Corticosteroid therapy led to rapid resolution of both the nodules and headache. This case highlights that EN-like panniculitis can represent a reactive manifestation of GCA rather than direct arteritic involvement, and that ultrasonography may support early diagnosis and treatment without the need for temporal artery biopsy.