Compressive myelopathy caused by isolated epidural myeloid sarcoma with systemic mastocytosis. Rare presentation of a hematological malignancy.

N manifestations of acute leukemia are due to direct involvement by meningeal infiltration and myeloid sarcoma; and indirect involvement by immunosuppression and treatment related side effects. It is rare for myeloid sarcoma to present without bone marrow involvement (isolated myeloid sarcoma or primary granulocytic sarcoma).1 It is even rarer for an isolated myeloid sarcoma to present in the epidural space. We evaluated a case of paraplegia admitted to our department. He had several atypical features that we would like to present in this report. A 39-year-old gentleman with a body weight of 58 kg presented with paresthesia and heaviness of both lower limbs of 4 days duration. He was found to have spastic paraplegia with bladder involvement and sensory level at T6. The clinical diagnosis of acute transverse myelitis was made. Table 1 summarizes the laboratory investigations. The MRI study of the dorsal spine (Figure 1) shows that a moderate sized enhancing posterior epidural component was compressing the thecal sac and spinal cord. Further work-up was carried out suspecting multiple myeloma/plasmacytoma. The peripheral blood picture showed dimorphic anemia, occasional large cells with granular cytoplasm and nucleus with condensed chromatin, and no blast cells. Ultrasound of the abdomen showed mild splenomegaly. Urine Bence Jones protein was absent. No M band was seen on serum protein electrophoresis. Bone marrow aspirate showed many large cells with abundant granular cytoplasm and some of them had multilobed nucleus probably mast cells. Bone marrow trephine biopsy showed normal cellularity, no plasmacytosis, or excessive blast cells. Clusters of cells were seen with abundant granular cytoplasm and vesicular nucleus. Immunohistochemistry showed 2 clusters of cells (20-22 cells per cluster), densely positive for CD117, with similar cells diffusely infiltrating the marrow. The cells tested negative for myeloperoxidase (MPO). Bone marrow findings were suggestive of mastocytosis and no evidence of leukemia or myeloma. He was started on steroids, and antihistamines. He was referred to neurosurgery for management of the extradural space occupying lesion. A T4-T9 laminectomy was carried out, and the epidural mass removed. The histopathology report showed myeloid sarcoma, possibly myelomonocytic type with mast cell proliferation (MPO positive, CD 117 positive Table 1 Laboratory investigations in a patient with the clinical diagnosis of acute transverse myelitis.