Hairy cell leukemia (HCL) is an infrequent neoplasm of mature B cells with rare neurologic involvement. These patients typically present with symptoms related to splenomegaly or cytopenia with rare neurologic involvement. Most neurologic involvement is predominately related to infection secondary to associated pancytopenia rather than neoplasm. To date, there are only three published reports of brain parenchymal involvement with variable treatment response and limited information on genetic profile. A 64-year-old male presenting with several neurological complaints including 2 months of headache and frequent falls is found to have laboratory and bone marrow biopsy results consistent with HCL. Notably, genetic testing was negative for the BRAF V600E mutation seen in classic HCL. MRI head with and without contrast showed innumerable T1 hyperintense rim-enhancing lesions in the bilateral cerebral hemispheres primarily concentrated in the frontal lobes. Neurosurgical biopsy was requested to resolve the diagnostic question of infection versus neoplastic etiology of the brain lesions. Pathology results and flow cytometry confirmed diagnosis of HCL brain involvement. Herein, we describe a case of diffuse HCL involvement of the brain in the framework of genetic variations to aid the understanding of this rare neurologic manifestation of HCL.
