Primary Central Nervous System Lymphoma Presenting with Peripheral Neuropathy; A Rare Case of Coincident PCNSL and Mononeuritis Multiplex

A 43-year-old male presented with diplopia and right sixth-nerve palsy. Brain magnetic resonance imaging (MRI) demonstrated a lesion in the right periventricular area. High-dose corticosteroid pulse therapy did not resolve the symptom. After one month, his diplopia progressed and he developed weakness of the left lower limb. Detailed examination revealed left sixth-nerve palsy, dropped foot, waddling gait, atrophy of the gluteal muscles and mild atrophy and weakness of the right upper limb. Neurological examination supported evidence of multiple cranial nerve palsies along with asymmetrical peripheral neuropathy. Electrodiagnostic studies were compatible with a mononeuritis multiplex. Rheumatologic evaluations were normal. Malignancy work-up were normal, except for some insignificant lymph nodes. Bone marrow aspiration and biopsy were normal. The second brain MRI detected multiple homogenous enhancing lesions in the right periventricular area.The result of stereotactic biopsy and immunohistochemistry staining demonstrated primary B-cell CNS lymphoma (PCNSL). Mononeuritis multiplex has not been reported as a paraneoplastic manifestation of PCNSL yet. In other words, it is not clear whether involvement of the peripheral nervous system in our patient is a paraneoplastic manifestation of PCNSL or a coincidence of PCNSL and hematologic lymphoma presenting with peripheral vasculitic neuropathy. It is recommendedthat future studies focus more on symptoms associated with PCNSL to recognize the exact relationship between PCNSL and peripheral neuropathy.