In ALS, motor neurons in the anterior horn of the spinal cord degenerate and die. In PDC neurons are affected in more widespread brain regions. These include the substantia nigra, hippocampus and cortex of the frontal, temporal and parietal regions. The pathology includes neuron loss, as well as the development of neurofibrillary tangles (NFT). NFT are intraneuronal lesions, consisting of highly insoluble forms of the microtubule-associated protein tau.
Neurofibrillary tangles are identical to those in AD, but no amyloid. E/M shows paired helical filaments.
Biochemically, the tangles comprise phosphorylated tau, in a similar pattern to that found in AD.
There is more insoluble tau in the white matter in PDC than in AD. ALS: neuron loss in the spinal cord, tangles there and to an extent in the hippocampus +/- neocortex PDC: extensive tangles in the hippocampus, neocortex, substantia nigra. Slightly different laminar distribution vs. AD – more superficial layers 2 and 3 in PDC.
There is no inflammation. ‘Asymptomatic’ Chamorro adults have NFT.