Atypical FTLD-FUS associated with ALS-TDP: a case report

A 30-year-old Japanese woman without relevant family history presented with a behavioral abnormality followed by motor weakness about 14 years later. The patient died at age 45. Post mortem examination revealed degeneration of the frontal and temporal lobes, as well as lower motor neurons in the brainstem and spinal cord. These features were reported previously as being consistent with a diagnosis of frontotemporal lobar degeneration (FTLD) with amyotrophic lateral sclerosis (ALS). In the present study, we show abundant fused in sarcoma (FUS)-positive dystrophic neurites but only a few neuronal cytoplasmic inclusions in the frontal and temporal cortices. TAR DNA-binding protein 43 (TDP-43)-positive inclusions were absent in the cerebrum. However, TDP-43-positive inclusions were present in the lower motor neurons of the brainstem and spinal cord. To our knowledge, this is the first report of a case in which FTLD-FUS pathology is of a dystrophic neurites-predominant type and FTLD-FUS is associated with ALS-TDP.