Skein-like inclusions in the anterior horn cells in motor neuron disease

Skein-like inclusions (SLIs) in the anterior horn cells of patients with motor neuron diseases, including familial amyotrophic lateral sclerosis with posterior column degeneration, sporadic lower motor neuron disease and classical amyotrophic lateral sclerosis, were investigated morphologically with hematoxylin and eosin preparations, immunostaining for ubiquitin and immunoelectron microscopy. The SLIs were thready linear or tubular structures which immunostained with antiubiquitin antibodies. They were detected on hematoxylin and eosin preparations as eosinophilic thread-like structures often surrounded by pale areas. SLIs were occasionally present as networks of threads or tubules. Sometimes, they were aggregated and formed larger pale inclusions. Ultrastructurally, the SLIs were bundles of filaments which appeared thicker than neurofilaments. The SLIs tended to have central hollow spaces which were devoid of filaments. When the SLIs were clustered, fuzzy thick filaments were randomly and loosely arranged among the individual SLIs. The SLIs were histologically and ultrastructurally distinct from other inclusions such as Bunina bodies and hyaline inclusions. This unique morphology of SLIs may provide a novel perspective on the degenerative processes of the anterior horn cells in MND.