Lower limb radiology of distal myopathy due to the S60F myotilin mutation

Abstract

Distal myopathies are a clinically and genetically heterogenous group of disorders in which the distal limb musculature is selectively or disproportionately affected. Precisely defining specific categories is a challenge because of overlapping clinical phenotypes, making it difficult to decide which of the many known causative genes to screen in individual cases. In this study we define the distinguishing magnetic resonance imaging findings in myotilin myopathy by studying 8 genealogically unrelated cases due to the same point mutation in TTID. Proximally, the vastii, biceps femoris and semimembranosus were involved with sparing of gracilis and sartorius. Distally, soleus, gastrocnemius, tibialis anterior, extensor hallicus and extensor digitorum were involved. This pattern contrasts with other distal myopathies and provides further support for the role of imaging in the clinical investigation of muscle disease.

Fig. 1

T₁ MRI images from cases of myotilinopathy. a Axial image at mid-thigh from an 81-year-old woman (Patient E) with predominantly distal lower limb weakness. Note fatty infiltration of semimembranosus (*), with sparing of gracilis (G) and sartorius (S). b Axial image at mid-calf from Patient E. Note extensive fatty infiltration of gastrocnemius (Ga), soleus (So) and tibialis anterior (TA). c Axial image at mid-thigh from a 68-year-old man (Patient D) with predominantly distal lower limb weakness. Note mild fatty infiltration of vasti (*), with sparing of sartorius (S) and gracilis (G). d Axial image at mid-calf from Patient D. Note fatty infiltration of medial gastrocnemius (Ga), soleus (So) and tibialis anterior (TA).