Morphological studies of sural nerve biopsies in the pseudopolyneuropathic form of amyotrophic lateral sclerosis.

The aim of this work was to study the neuropathological picture of the sural nerve in the pseudopolyneuropathic form of amyotrophic lateral sclerosis (ALS). Five patients were considered: in all cases the clinical and electromyographic follow-up excluded other diseases. EMG-studies were repeatedly performed: they showed the progressive evolution of the spinal anterior horn cell pathology from lower spinal to cervical levels. The sural nerve was removed and immediately fixed in phosphate-buffered 2.5% glutaraldehyde and processed according to the procedure used in our laboratory for light and ultrastructural microscopy. Quantitative analysis of myelinated fiber density was carried out on photographic enlargements of 1 micron semithin sections and recorded on histograms. The light and ultrastructural findings revealed a severe loss of myelinated fibers, the decrease affecting all types of fibers, but predominantly the largest ones. In the teased fibers, Wallerian-like degeneration was observed. In the axons there was an increase of mitochondria, dilatation of the small vesicles, and an increase in the number of neurofilaments. It can be assumed from the histopathologic data that the neuropathologic pattern in the pseudopolyneuropathic form of ALS shows an axonal degeneration. It is our opinion that the histopathologic data obtained in the sural nerve biopsy in this form of ALS reveals a clear involvement of the sensory neurons of the spinal ganglia, and the results can be useful for the study of precocious lesions in ALS.