Invited commentary. Clinical and magnetic resonance imaging features of 'diamond on quadriceps' sign in dysferlinopathy.

BACKGROUND There is very little by way of clinical examination that helps in the diagnosis of subtypes of limb-girdle muscular dystrophy (LGMD). A small observation led to this study on a clinical sign in a group of 31 patients with dysferlinopathy that included 13 with LGMD-2B and 18 with Miyoshi myopathy (MM). The patients were asked to stand with knees slightly bent so that the quadriceps muscles were in moderate action. Those who could not stand in this posture due to muscle weakness were observed during sitting-down and standing-up in slow motion keeping hands away from thighs. Upper half of the anterolateral aspect of thighs was observed for any abnormal bulge. Twenty one (eight with LGMD-2B and 13 with MM) were found to have diamond-shaped bulge in this region with wasting of muscles above and below. This bulge was not apparent in standing or sitting position when quadriceps muscle was not in action. T1-weighted MRI of the thighs revealed focal bulge-out of muscle fibers during contraction. Among the patients with other types of muscular dystrophy, who served as controls, one with clinical diagnosis of sarcoglycanopathy had multiple mild bulges visible over the quadriceps muscle but none showed diamond-shaped or little elongated single bulge as was seen in dysferlinopathy. CONCLUSIONS We infer that nearly two-thirds of the patients with dysferlinopathy demonstrate 'diamond on quadriceps' sign. Further studies are needed to look for its specificity among patients with muscular dystrophy.