A Case of Asymptomatic Hairy Cell Leukemia with Multifocal Spinal Involvement

The patient was a 51-year-old man who was diagnosed as having prostate cancer(adenocarcinoma)in December Year X-3. He underwent total prostatectomy in June Year X-2. The lesions were confined to the right lobe of the prostate. Examinations revealed no evidence of metastasis. At the same time, he developed bicytopenia, with a serum soluble interleukin-2 receptor(sIL-2R)level of 4,137 U/mL(220-530). Examination of a naturally dried peripheral blood smear revealed one cell that resembled a hairy cell. Genetic analysis of a blood specimen revealed no BRAF exon 15 mutation(V600E). Bone marrow examination showed no abnormalities. Positron emission tomography/computed tomography(PET/CT)revealed mild accumulation at multiple sites, but localized to the vertebrae. Magnetic resonance imaging(MRI)showed abnormal signals in the vertebrae. We performed vertebral biopsy of Th12, and histopathological examination revealed the diagnosis of hairy cell leukemia(HCL). Genetic analysis of the biopsy specimen also revealed a BRAF exon15(V600E)mutation. Since he had no clinical symptoms, he was carefully followed up without treatment. In April Year X, he still remained asymptomatic, and his blood counts had improved spontaneously. However, a repeat PET/CT revealed increased accumulation in the spine. Bone lesions due to bone invasion of HCL are mainly caused by bone resorption, and TNF-α is considered to be closely involved in the development of the osteolytic lesions. The finding of these bone lesions suggested that he was at risk for the development of compression fractures.