A 59-year-old man with primary myelofibrosis developed motor and sensory neurological disturbance of the legs. Magnetic resonance imaging (MRI) demonstrated a mass lesion of the thoracic vertebra at Th4-6, and in the thoracic vertebral canal at Th4-9, which compressed the spinal cord. Needle biopsy of the mass lesion demonstrated extramedullary hematopoiesis. Initial treatment with bolus methylprednisolone was ineffective and, after subsequent radiation therapy, the mass lesion disappeared and the neurological symptoms ameliorated; however, regrowth of the extramedullary lesion was observed one month later. Surgical resection of the extramedullary lesion, laminectomy, and subsequent radiation were performed. The clinical course after the final treatment was good with no neurological symptoms, although the follow-up period is still short.
