Fibrous dysplasia masquerading as extramedullary relapse after bone marrow transplantation for chronic myeloid leukemia.

A 19-year old girl suffered from relapse of chronic myeloid leukemia (CML) after bone marrow transplantation. The disease was controlled by interferon and imatinib mesylate, but was complicated by autoimmune hyperthyroidism. She presented with unilateral proptosis with no extraocular muscle or visual defect at 26 months follow-up. Systemic investigations showed no recurrence of leukemia or thyrotoxicosis. Magnetic resonance imaging revealed an extensive retro-orbital base of skull lesion. A trans-oral biopsy showed fibrous dysplasia and continuous observation was advised. The unusual sequence of events and the differential diagnoses for unilateral proptosis in post bone marrow transplantation (BMT) cases are discussed.