Primary cutaneous large B cell lymphoma masquerading as lupus vulgaris.

Primary cutaneous large B cell lymphoma, leg type is a rare and aggressive variant of cutaneous B cell lymphoma. It predominantly affects elderly women, with the lower limb being the most common site of presentation. The overall prognosis is poor, compared to other cutaneous B cell lymphomas. A 47-year-old man presented with a progressively enlarging nodule over the medial aspect of the left foot since 2 months. Clinical examination revealed a nodular plaque-like lesion with central ulceration that measured 7 × 7 cm, firm in consistency, and with ill-defined margins. The initial clinical diagnosis was lupus vulgaris. An incision biopsy was done, which on histopathology and immunohistochemistry revealed a rare diagnosis of primary cutaneous B cell lymphoma, leg type. The patient was started on chemotherapy; however, he succumbed to his illness about 1 year after the initial presentation. It is a rare type of cutaneous lymphoma, which may masquerade infectious disorders such as lupus vulgaris. A detailed histopathological and immunohistochemical analysis is essential for its correct diagnosis and management. Only a handful of cases of this rare condition are reported to date. This case has been reported in view of its rarity and unusual clinical presentation.