Motor involvement in frontotemporal lobar degeneration with TAR DNA-binding protein of 43 kDa type C

The degeneration of pyramidal tracts has been reported in frontotemporal lobar degeneration with TDP-43 (TAR DNA-binding protein 43) pathology (FTLD-TDP) type C. Herein, we examined the detailed pathology of the primary motor area and pyramidal tracts in the central nervous system in four autopsy cases of FTLD-TDP type C, all of which were diagnosed by neuropathological, biochemical, and genomic analyses. Three patients showed right dominant atrophy of the frontal and temporal lobes, while the other patient showed left dominant atrophy. All four patients showed motor symptoms, and two patients had episodes of repeated aspiration. In the primary motor area, phosphorylated TDP-43 (p-TDP-43) or annexin A11-immunoreactive long dystrophic neurites were observed in all cases, and neuronophagia of the Betz cells was frequently observed in two of four cases. In the lower motor system, p-TDP-43 or annexin A11-positive dystrophic neurites were detected in the anterior horn of the spinal cord. Immuno-electron microscopy of the insoluble fraction extracted from all cases showed p-TDP-43 or annexin A11-labelled filaments. In FTLD-TDP type C, neurodegeneration with TDP and annexin A11 pathology was observed mainly in the upper motor neurons of both patients with right- and left predominant temporal atrophy and a short disease duration. Furthermore, a combination of TDP-43 and annexin A11 pathology was visible in the lower motor neurons, albeit less frequently. In summary, we reported the TDP-43 and annexin A11-associated involvement of anterior horn cells of the spinal cord for the first time. The degeneration of the motor system could contribute to dysphagia and aspiration pneumonia at the late stage of FTLD-TDP type C. Little or no TDP pathology was found in the corticospinal tract, unlike in FTLD-TDP type B, suggesting the occurrence of secondary degeneration in FTLD-TDP type C.