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Findings: There is prominent sclerosis involving the terminal tuft of the great toe, extending the entire length of the phalanx medially. Additionally, there is a linear area of sclerosis in the distal medial proximal phalanx. A small round area of sclerosis is seen in the head of the hallux metatarsal.

Diagnosis: 1. Melorheostosis of the distal and proximal phalanges of the hallux (biopsy proven). 2. Enostosis (bone island) of the head of the hallux metatarsal.

Discussion: Melorheostosis is an uncommon nonhereditary sclerosing bone disorder which often presents with pain and decreased range of motion, though it may often be detected incidentally. Our patient, seen at the proverbial outside hospital, underwent biopsy which was consistent with the radiographic diagnosis of melorheostosis. Association with the other sclerosing bone dysplasias (osteopoikilosis, osteopathia striata my be seen, and is known as mixed sclerosing bone dystrophy. This may in turn be associated with vascular and/or lymphatic anomalies, or Trevor's disease. Isolated melorheostosis may be associated with linear scleroderma, neurofibromatosis, or tuberous sclerosis, as well.

The typical distribution is sclerotomal in one or more bones of an extremity. The axial skeleton can also be involved, however, either separately or in conjunction with extremity findings.

Plain film radiography shows characteristic changes:

• peripherally located wavy hyperostosis ('flowing candle wax')
• single or multiple bones in a limb, "crossing" joints
• may see endosteal hyperostosis
• may see adjacent mineralized soft tissue masses

References:
Yu JS et al. Melorheostosis with an ossified soft tissue mass: MR features.
Skeletal Radiology. 24: 367-70, 1995.

Resnick D and Niwayama G. Enostosis, hyperostosis, and periostitis, In: Diagnosis of Bone
and Joint Disorders, 3rd ed. D Resnick, editor. W.B. Saunders Co., Philadelphia,
1995. Vol. 6, pp 4396-4415.

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