Exostoses, enchondromatosis and metachondromatosis; diagnosis and management.

We describe a 5 years old girl who presented to the multidisciplinary skeletal dysplasia clinic following excision of two bony lumps from her fingers. Based on clinical examination, radiolographs and histological results an initial diagnosis of hereditary multiple exostosis (HME) was made. Four years later she developed further lumps which had the radiological appearance of enchondromas. The appearance of both exostoses and enchondromas suggested a possible diagnosis of metachondromatosis. Genetic testing revealed a splice site mutation at the end of exon 11 on the PTPN11 gene, confirming the diagnosis of metachondromatosis. While both single or multiple exostoses and enchondromas occur relatively commonly on their own, the appearance of multiple exostoses and enchondromas together is rare and should raise the differential diagnosis of metachondromatosis. Making this diagnosis is important as the lesions in metachondromatosis may spontaneously resolve and therefore surgical intervention is often unnecessary. We discuss the diagnostic findings, genetic causes, treatment and prognosis of this rare condition of which less than thirty cases have previously been reported.