musculoskeletal and connective tissue disorders
Benign Bone Tumors and Cysts
Melorheostosis
Melorheostosis is a rare developmental disease of cortical bone. It is a mesenchymal dysplasia of the cortex that may be linked to a random MAP2K1 gene mutation. The process starts in childhood with thickening of the bone cortex on both the outer surface (periosteal) and inner surface (endosteal). The process proceeds very slowly in the cortex. Melorheostosis usually affects only a single bone (monostotic) but may affect other bones (polyostotic) of the same limb (somatic distribution). The tibia and femur are common sites. Patients often present with discomfort, and x-rays demonstrate thickening of the cortex of the involved bone. The radiographic appearance may suggest traumatic new bone formation, a stress fracture, or even an osteosarcoma. However, the dense cortical thickening has a characteristic “dripping candle wax” appearance (irregular cortical hyperostosis), and image stability on serial x-rays is sufficient to make the diagnosis without biopsy. Discomfort is treated with analgesics or anti-inflammatory agents, and serial x-rays are done over time. Attempts at surgical removal or en bloc resection for severely painful lesions have usually not been successful, and on very rare occasions, amputation is needed. This CT scan shows the dense bone lesions of melorheostosis in the femur and pelvis. Image courtesy of Michael J. Joyce, MD, and David M. Joyce, MD. This x-ray shows melorheostosis in the proximal femur and pelvis of a 42-year-old patient. Image courtesy of Michael J. Joyce, MD, and David M. Joyce, MD. This x-ray shows the "dripping candle wax" appearance of melorheostosis in the femur of a 39-year-old patient. Image courtesy of Michael J. Joyce, MD, and David M. Joyce, MD. 