Predominant distal muscle involvement in spinal muscular atrophy

Spinal muscular atrophy (SMA) is an autosomal recessive disorder characterized by degeneration of alpha motor neurons, clinically associated with muscle weakness, hypotonia and muscle atrophy. The weakness is predominant in the proximal muscles, with lower limbs often more involved than upper limbs with a typical distribution [1]. In the most severe cases the involvement is more diffuse affecting both proximal and distal muscles with very limited movements of hands and feet. The predominant proximal involvement has also been observed on muscle Magnetic Resonance Imaging (MRI) [2,3].