Paget's bone disease is not always the culprit

A 48-year-old woman, who was previously diagnosed with Paget's bone disease, referred to our Metabolic Bone Diseases Outpatient Clinic complaining of chronic, non-traumatic pain at the left foot. Clinical examination revealed that the left forefoot, as opposed to the right one, was enlarged, deformed and painful on finger pressure, particularly at the metatarsal and the 2nd interphalangeal joint level. Skin upon the 2nd toe appeared slightly thickened.

She was subjected to an X-ray, which showed a sclerosing lesion of the metatarsus and the first phalange of the left second toe (Fig. 1a-b ). Subsequently, a 99 m Tc-medronate bone scan revealed a pathologic uptake of radionuclide at the left foot (Fig. 1c).

Routine laboratory exams were all in the normal range, included 25-OH vitamin D and bone turnover markers.

In order to investigate the nature of this sclerosing condition, the patient was subjected to bone biopsy, which showed a marked trabecular remodeling, a reduction in the number of osteoclasts and fibrous metaplasia of the medullary tissue (Fig. 1d).

What is the diagnosis?

Melorheostosis.

After careful review of the patient's medical history, clinical, laboratory and instrumental examinations, but most importantly bone biopsy, we formulated a diagnosis of melorheostosis. Melorheostosis is a rare form of non-hereditary sclerosing bone dysplasia. The name derives from the Greek term melos (limb) and rhein (to flow) []. The etiology is not well known, although there have been reports of melorheostosis associated with mutation loss of function in LEMD3 gene []. Melorheostosis is most frequently diagnosed in young adults, without sexual predilection. Often melorheostosis is monomelic and affects one or more contiguous bones in particular in lower extremities. It may be asymptomatic or present with pain, stiffness, deformities and limitation in movement with the involvement of soft tissue and skin that appears tense. Generally, laboratory tests are normal. Radiographs typically show flowing hyperostosis and “candle-wax-like” thickening. Bone scan often reveals accumulation of radionuclide in the area of the lesion. Bone biopsy shows variable degrees of fibrosis with mixed areas of lamellar and woven bone []. Melorheostosis is often mistaken for a Paget's bone disease. This latter can affect any bone segment, determining enlargement and deformation, but unlike melorheostosis, it often affects the axial skeleton, is generally accompanied by increased alkaline phosphatase and does not alter, at least in the early stages, the soft tissue over bone lesions [].