Is motor neuron disease-inclusion dementia a forme fruste of amyotrophic lateral sclerosis with dementia? An autopsy case further supporting the disease concept.

We report the autopsy findings of a 62-year-old man who exhibited progressive FTD 10 years before the appearance of muscle weakness and wasting, and who died approximately 11 years after onset of the symptoms. Degeneration and atrophy of the frontal and temporal lobes, which contained ubiquitin-positive neuronal inclusions and dystrophic neurites, were evident. Circumscribed degeneration affecting the hippocampal CA1-subiculum border zone was also a feature. Moreover, degeneration was present in both the upper and lower motor neuron systems, the latter being more severely affected. A few lower motor neurons were found to contain the cytoplasmic inclusions characteristic of ALS (i.e. Bunina bodies and ubiquitin-positive skeins). Also of interest was the presence of pallidonigroluysian atrophy, which appeared to be responsible for the chorea-like involuntary movements that developed in this patient approximately 2 months before death. The clinical and pathological features of our patient further support the idea that motor neuron disease-inclusion dementia (MND-ID), which has been classified as a pathological subgroup of FTD, is a forme fruste of ALS with dementia. In other words, if patients with MND-ID live long enough, they may develop ALS.