Muscle biopsy in juvenile distal spinal muscular atrophy.

The myopathological changes in properly selected muscles can allow evaluation of the definite distribution of neuronogenic denervation which can probably not be found by clinical examination or EMG study of inadequate muscle sampling. We performed muscle biopsies in 13 Chinese patients with chronic juvenile monomelic motor neuron disease involving the distal part of the upper extremities. According to our findings and the literature review, the neurogenic changes selectively affected the muscles innervated by C7, 8 and T1 spinal nerves while sparing others. Consequently, the term 'juvenile lower cervical spinal muscular atrophy' is suggested.