Paraneoplastic multicentric reticulohistiocytosis: a clinicopathologic challenge.

Multicentric Reticulohistiocytosis (MRH) is a rare, systemic non-Langerhans cell histiocytosis (non-LCH) with prominent joint and skin manifestations. It is mostly self limiting. However, 15-30% of the cases are associated with malignancy and carry a poor prognosis. We report the case of a 42-year-old man who presented with multiple reddish-brown papules that on biopsy showed aggregates of oncocytic histiocytes with several multinucleate giant cells. Immunostains were positive for CD 68, CD 45 and were negative for S-100, CD1a. An impression of multicentric reticulohistiocytosis (MRH) was made, with the recommendation to screen for malignancy. Electron microscopy of the skin lesions showed features consistent with non-Langerhans cell histiocytosis. The patient was later diagnosed with acute myeloid leukemia at a follow-up visit several months later. Thus, it appears prudent to screen and follow-up adults with MRH, to identify an underlying malignant condition.