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Metachondromatosis (MC) is a rare disorder characterized by the presence of both multiple enchondromas and osteochondroma-like lesions.
The prevalence is unknown and fewer than 40 cases have been reported.
The first signs of MC occur during the first decade of life. Most frequently, osteochondromas occur in the hands and feet, predominantly in digits and toes, and enchondromas involve the iliac crests and metaphyses of long bones. Osteochondromas are small and point towards the adjacent growth plate. MC does not lead to shortening or bowing of the long bones, joint deformity, or subluxation. The lesions spontaneously decrease in size or regress.
Loss-of-function mutations, including deletions, non-sense mutations and splice sites mutations, of the PTPN11 gene (12q24) have been linked to MC in several families.
Diagnosis is based on clinical signs, radiographic findings and familial history. The radiographic features are osteochondromas at the metaphyses of the short tubular bones (hands and feet) pointing towards the joints and coexisting with enchondromas.
The differential diagnosis should include hereditary multiple osteochondromas (MO; see this term) in which the long bones are predominantly affected and the lesions point away from the joint/growth plate and may result in shortening or deformity of the affected bones. Other diseases to be considered include the non-hereditary conditions Ollier disease and Maffucci syndrome (in which multiple enchondromas are found in the medulla of the bone and are predominantly unilateral), and dysplasia epiphysealis hemimelica (DEH; characterized by a cartilaginous overgrowth mainly located in the lower extremities on one side of the body) (see these terms).
Antenatal diagnosis is technically feasible.
MC has an autosomal dominant mode of inheritance. Genetic counseling may be proposed to the patients and their families.
Management and treatment
For severe malalignment of the fingers/toes, surgical intervention can be considered to remove osteochondromas.
No malignant transformation has been reported so far. Clinical course is unpredictable as there may be simultaneous growth of some of the lesions and regression of others. Nerve paralysis or vascular complications (avascular necrosis of the femoral head; see this term) may occur.