A Rare Case of Acute Aleukemic Mast Cell Leukemia With Osteoblastic Lesions in the Appendicular Skeleton.

Mast cell leukemia (MCL) is a rare and aggressive form of systemic mastocytosis (SM) that commonly involves the bone. This often presents as osteoporosis with focal osteolytic lesions and pathological fractures. Osteoblastic (sclerotic) lesions are rarely seen in MCL. The vertebral bodies are the most common site of bone involvement, with lesions outside of the axial skeleton being extremely rare. MCL presenting with osteoblastic lesions has been reported in the literature, however, there are no reported cases of osteoblastic lesions in the appendicular skeleton. Here we report a rare case of acute aleukemic MCL that presented with diffuse osteoblastic/sclerotic osseous lesions involving ribs, thoracic spine, lumbar spine and pelvis without pathological fractures.