Objective:

Background:

HIBM, aka GNE or Nonaka myopathy, is a rare autosomal recessive disease characterized by progressive muscle weakness, often affecting the distal leg first with characteristic sparing of the quadriceps muscle. Diagnosis should be considered based on this unique clinical presentation in combination with characteristic muscle findings on EMG, MRI, or biopsy. This disease can be confirmed with genetic testing.  

Design/Methods:

NA

Results:

The patient first noticed difficulty with stairs at 25 years old. She was evaluated by multiple physicians over the following years. Work up, including MRI of the spine and blood work, was notable for mild disc herniations and mild-to-moderate degenerative changes in the spine. Two EMGs done earlier in her course revealed decreased amplitudes in the peroneal compound muscle action potential (CMAP) and were interpreted as neurogenic in etiology.  Her symptoms continued to progress with gait instability and arm weakness. Muscle strength was graded as 3+/5 in bilateral knee flexion with preserved 5/5 knee extension, 0/5 foot dorsiflexion and 3+/5 in finger flexion with preserved 5/5 finger extension. Given this pattern of weakness a diagnosis of HIBM was considered. Nerve conduction studies were repeated and continued to show decreased motor amplitudes. This was now thought to be due to muscle atrophy as the needle EMG showed evidence of diffuse myopathy. MRI of the thigh confirmed the quadricep sparing with fatty-fibrous replacement of the posterior compartment muscles. Genetic testing confirmed the diagnosis of HIBM.  

Conclusions:

This case highlights the importance of recognizing the characteristic pattern of weakness in order to diagnose this rare myopathy. It also calls attention to the fact that decreased CMAPs can be seen in both neurogenic and myopathic etiologies when significant muscle atrophy is present.