Abstract
Diagnosing B-cell lymphoma-associated mononeuritis multiplex is challenging due to its rarity and the potential co-existence of other causes of mononeuritis multiplex. Here, we report a case of a 74-year-old male who initially presented with left cranial neuropathies followed by right-sided extremity weakness with hyporeflexia, right facial involvement, and subsequently asymmetric weakness and multifocal muscle wasting. Minor improvements were observed with multiple rounds of steroid treatment. The diffuse large B-cell lymphoma diagnosis was eventually established six months later upon a repeat mediastinal lymph node biopsy and cerebrospinal fluid cytology. A nerve biopsy demonstrated severe axonal neuropathy with loss of axons in all fascicles without evidence of vasculitis. A muscle biopsy showed atrophy in both type 1 and type 2 fibers. A presentation of mononeuritis multiplex warrants concern for B-cell lymphoma, mainly when other mechanisms of peripheral neuropathy are less likely.