Cutaneous large B-cell lymphoma of the leg: presenting initially as mononeuritis multiplex.

We report a rare case of primary B-cell lymphoma of the leg presenting with mononeuropathy multiplex. A 79-year-old Chinese woman who was being investigated for mononeuritis multiplex had an incidental finding of indurated erythematous plaques on the breast and left leg. A skin biopsy from the nodular area on the right breast showed a dense and diffuse infiltrate of atypical cells with large, round, hyperchromatic nuclei with prominent nucleoli. These atypical lymphocytes were CD20+, Bcl-2+ and Mum-1+. A diagnosis of diffuse large B-cell lymphoma, leg type involving the breast and leg with extracutaneous involvement, was made. This case highlights the importance of a full systemic and cutaneous examination in patients presenting with progressive, painful peripheral neuropathy.