A fine structural study of Onuf's nucleus in sporadic amyotrophic lateral sclerosis

Onuf's nucleus of the second sacral spinal cord level was examined in twelve patients with sporadic amyotrophic lateral sclerosis (ALS). Under light-microscopic examination, the neurons of Onuf's nucleus were well-preserved in contrast with the severe neuronal depletion of the anterior horn cells. Ultrastructurally, however, substantial pathological changes such as Bunina bodies (BB), randomly arranged filaments associated with fine granules corresponding to Lewy body-like hyaline inclusions (LBHI) and bundles of tubular filaments corresponding to skein-like inclusions (SI) all of which are characteristic features of ALS, were demonstrated ubiquitously in the Onuf's nucleus in eleven of twelve patients. These changes may be of a reactive nature and represent an initial change of neuronal degeneration, since no definite cell destruction was observed in the nucleus. The changes in the Onuf's nucleus correlated with the changes observed in the anterior horns, although to a lesser degree. The more BB, LBHI and SI were observed in the anterior horns of patients with ALS, the more these inclusions were observed in Onuf's nucleus. Thus, we conclude that Onuf's nucleus is also affected by pathological changes in ALS.