Atypical lower motor neuron disease with enlargement of Nissl substance: Report of an autopsy case

The patient was an 81-year-old woman diagnosed with atypical motor neuron disease who died after a long clinical course (7.5 years without mechanical assistance of ventilation) characterized by lower motor neuron signs and symptoms. Upper motor neuron signs and cognitive impairment were not apparent. Autopsy demonstrated severe neuronal loss in the anterior horn of the spinal cord, and some of the remaining neurons showed enlargement of Nissl substance and apparent thickening of the nuclear envelopes. No Bunina bodies, skein-like inclusions, or structures immunoreactive for phosphorylated transactivation response DNA-binding protein 43 were found. Immunoreactivity for superoxide dismutase-1 was focally seen in the enlarged Nissl substance. Ultrastructural examination demonstrated an increase of rough-surfaced endoplasmic reticulum (rough ER) and free ribosomes, disaggregation of polyribosomes, and dispersion of free ribosomes. Cisterns of rough ER were slightly dilated, and some of them were closely attached to the nuclear envelopes. Enlargement of Nissl substance may be related to "ER stress", and the abnormal findings of rough ER and free ribosomes may represent a degenerative process. However, another possibility, that they represent a compensatory hyperplastic change, cannot be excluded. The close attachment of cisterns of rough ER to the nuclear envelopes may be a mechanism to support or compensate for the abnormally-fragile nuclear envelopes.