Granulomatous mastitis during pregnancy with sudden onset of gait difficulty and erythema nodosum: A case report and review of the literature

Abstract Granulomatous mastitis (GM), a benign inflammatory disease of the breast, often mimics breast cancer on presentation. We present a case of GM during pregnancy manifesting as a breast mass, sudden onset of plantar pain, and erythema nodosum (EN). A 31‐year‐old pregnant Japanese woman, gravida 2, para 1, was referred to our hospital with severe plantar pain on both soles, causing difficulty walking. This pain worsened and EN appeared on both lower legs, followed by a left breast mass. Ultrasound findings suggested malignancy; however, aspiration biopsy confirmed GM. Her arthritis and EN resolved 2 days after commencing oral prednisolone and her walking improved. EN with/without arthritis is commonly associated with GM, especially during pregnancy. The described manifestations with a breast mass are suggestive of this diagnosis.