Selective loss of small myelinated and unmyelinated fibers in Shy-Drager syndrome.

The number and sizes of myelinated and unmyelinated fibers in biopsied sural nerves in cases with Shy-Drager syndrome were studied in comparison with cases with olivopontocerebellar degeneration not having autonomic dysfunction. In Shy-Drager syndrome there was a tendency for both small myelinated and unmyelinated fiber densities to be reduced in comparison with cases with olivopontocerebellar degeneration. Unmyelinated fibers more than 0.5 micrometers in diameter were significantly reduced in Shy-Drager syndrome, a fact suggesting myelinated fiber degeneration. Multilamellated Schwann cell processes, isolated Schwann cell processes, and collagen pockets were more numerous and conspicuous in cases with Shy-Drager syndrome. It was concluded that unmyelinated fibers and small myelinated fibers in the peripheral nerves were involved selectively in Shy-Drager syndrome. The significance of the findings was discussed in terms of autonomic dysfunction observed clinically.