Clinical history: 63 year old female with a nodule on the extensor surface of her right elbow.
What is the most probable diagnosis?
Rheumatoid nodules develop in up to 25% of patients with rheumatoid arthritis and tend to present in patients with severe disease. There is a higher incidence in females and the lesions most commonly occur on the extensor surfaces of the extremities.
Grossly, the lesions are firm, erythematous to skin-coloured subcutaneous nodules which may adhere to the underlying fascia or bone.
Histologically, the nodules are located within the dermis or subcutaneous tissue and are comprised of an extensive central zone of eosinophilic necrobiosis (degenerating collagen) surrounded by an infiltrate of giant cells, histiocytes and lymphocytes in a palisading pattern. The central necrobiotic zone contains fibrin and there is associated dermal fibrosis and chronic inflammation.
The differential diagnosis includes subcutaneous granuloma annulare and necrobiosis lipoidica. Immunohistochemistry is not contributory. Prognosis depends on the severity of underlying disease and although treatment is directed at treating the underlying rheumatoid arthritis, the nodules may be excised if symptomatic.