NEB mutations are the most frequent causes of autosomal recessive subtypes of nemaline myopathies (NMs). There are few studies on muscle magnetic resonance imaging (MRI) changes in NEB-related NMs. We aimed to characterize the diagnostic and prognostic value of muscle MRI patterns in NEB-related NMs. Twenty-one patients with confirmed diagnoses of NEB-related NMs were enrolled. The relationships between MRI changes in lower extremity muscles and clinical features were investigated. Most patients (18/21) presented with lower limb muscle weakness, with a distal predominance. In the lower limbs, the mean fatty infiltration score was greatest in the soleus (2.44), followed by the gastrocnemius (2.00) and gluteus maximus (2.05). The severity of fatty infiltration in the thigh muscles was correlated with age at the time of MRI (r = 0.569, p = 0.009) and disease duration from symptom onset to MRI (r = 0.597, p = 0.005). The mean fatty infiltration scores of the gluteus maximus, vastus medialis, sartorius, and adductor maximus were moderately correlated with disease duration (r-values = 0.467-0.597). Our study revealed that the degree of lower limb muscle fatty infiltration in NEB-related NMs was correlated with the disease course, with the gluteus maximus of the thigh and soleus of the calf being the most severely affected. Edema of the lower limb muscles was also more common and noticeable in the calf than in the thigh. These muscle MRI changes may be helpful in the diagnosis and follow-up of this disease.

Congenital myopathies (CM) are a group of rare inherited muscle disorders characterized by particular histopathological alterations on muscle biopsy. Core-rod myopathy is a CM presenting with cores and rods as distinctive muscle morphological features. We describe 3 young patients presenting congenital core-rod myopathy with bilateral foot-drop associated with autosomal recessive nebulin gene (NEB) mutations detected by exome sequencing. This report illustrates that core-rod congenital myopathy with foot-drop is frequently associated with NEB gene mutations and should be considered in the differential diagnosis of early onset distal myopathies.