Mild metatropic dysplasia: emphasis on the magnetic resonance imaging of articular cartilage thickening

Metatropic dysplasia (MD) is a rare skeletal disorder characterized by short stature due to epiphyseal cartilage and growth plate abnormalities. The severity of MD varies from mild to lethal. This disorder is caused by mutations in the transient receptor potential vanilloid 4 (TRPV4) that encodes calcium-permeable, nonselective cation channels. A 33-year-old female presented at our hospital with a history of worsening knee pain diagnosed at the previous institution as a case of osteoarthritis. Radiographs of the knee showed epiphyseal irregularity without joint space narrowing. On MRI, fat-suppressed proton density-weighted imaging revealed thickened articular cartilage with a smooth surface and an abnormal signal intensity of the subchondral bone; T(1) weighted imaging demonstrated irregularity of the epiphysis. These findings and the familial history (both her children had TRPV4 mutations) led to the suspicion that her condition could be due to mosaicism for TRPV4 mutation. To the best of our knowledge, this is the first report of MRI findings focusing on articular cartilage thickening in a patient with mild MD. Bone dysplasia including MD should be considered in young patients with articular cartilage thickening and subchondral bone irregularities on MRI.