Waldenström Macroglobulinemia-Associated Peripheral Neuropathy in the Brachial Plexus With Bing-Neel Syndrome Diagnosed Through Repeated Cerebrospinal Tests.

In Waldenström macroglobulinemia (WM), confirming the presence of Bing-Neel syndrome (BNS) is important because drugs that penetrate the central nervous system (CNS) must be selected. We report the case of a 75-year-old man for whom tirabrutinib, a second-generation Bruton's tyrosine kinase inhibitor (BTKi), was useful in treating WM-associated peripheral neuropathy (PN) with BNS. Numbness and muscle weakness in the fingers occurred three years after the initial treatment of WM. WM-associated PN due to demyelinating disease was diagnosed based on the results of a nerve conduction study and magnetic resonance imaging showing bilateral symmetric swelling of the brachial plexus. The cerebrospinal fluid (CSF) cytology results were initially negative; however, the CSF test was repeated because of extremely high protein levels (984 mg/dL) and slightly elevated leukocyte counts (14/µL). The second test revealed abnormal lymphoplasmacytic cells (189/µL), indicating BNS. Rituximab and high-dose methotrexate-containing chemotherapy were administered. Despite the subsequent negative CSF cytology results, his neurological symptoms persisted but subsided soon after the initiation of tirabrutinib. The therapeutic effects of tirabrutinib persisted for 25 months. This case suggested that a careful search for concurrent BNS is important when lesions are close to the CNS or when atypical CSF findings are obtained in patients with WM-associated PN, especially when BTKi options are available.