[A Case of Bing-Neel Syndrome With Repeated Long Spinal Cord Lesions].

The patient was a 45-year-old man. Since 2019, he had exhibited repeated steroid-improved dysuria and long spinal cord lesions. At the time of recurrence in June 2020, he exhibited a marked increase in serum IgM levels, suggesting hematopoietic disease. We found an MYD88 L265P mutation in cerebrospinal fluid cells, which subsequently led to the diagnosis of Bing-Neel syndrome (BNS). The patient was treated with Burton's tyrosine kinase inhibitors and his condition progressed without dysuria or worsening of the imaging findings. This case was challenging to differentiate from intractable inflammatory diseases; however, the identification of hyper-IgM helped in the diagnosis. BNS should be differentiated from central nervous system lesions through the identification of hyper-IgM.