Primary Central Nervous System Histiocytic Sarcoma During Neuromyelitis Optica Spectrum Disorder

Abstract

Histiocytic sarcoma (HS) is a rare hematopoietic malignancy that is seldom found with primary involvement in the central nervous system (CNS). 1-4 Neuromyelitis optica spectrum disorder (NMOSD) is an autoimmune demyelinating disease characterized by anti-aquaporin-4 antibodies (AQP4-Ab). We report an exceedingly rare case of primary-CNS-involvement HS (PCNSHS) occurring during the clinical course of NMOSD. A 64-year-old female with a history of cervicothoracic posterior decompression surgery presented with right lower-limb weakness, paresthesia, and gait disturbance. Her medical history included hypertension, dyslipidemia, and Graves’ disease. A neurological examination showed bilateral lower-limb weakness, sensory disturbances, and upper-limb hyperre-flexia. Her Expanded Disability Status Scale (EDSS) score was 7.5. A cerebrospinal fluid (CSF) analysis revealed pleocytosis (39 cells/μL) with 97% mononuclear cells, elevated protein (3.12 g/L), and positive oligoclonal bands. AQP4-Ab were elevated in both serum (14.2 U/mL in an enzyme-linked immunosorbent assay [ELISA], with positivity in a cell-based assay [CBA]) and CSF (4.2 U/mL in ELISA). Spinal T2-weighted MRI revealed extensive hyperintense lesions spanning the thoracic spinal cord, with heterogeneous gadolinium enhancement, which was consistent with longitudinally extensive transverse myelitis (LETM) (Fig. 1A). She was diagnosed with NMOSD. Her symptoms improved after treatment with high-dose intravenous corticosteroids, plasma exchange, and maintenance therapy with azathioprine and prednisolone. She regained the ability to walk and was transferred