Reduction of Small Fibers of Thoracic Ventral Roots and Neurons of Intermediolateral Nucleus in Parkinson Disease and Dementia with Lewy Bodies.

Background And Objective: Loss of intermediolateral nucleus (IML) neurons is considered to play a major role in orthostatic hypotension (OH) of multiple system atrophy (MSA). In Parkinson disease (PD) and dementia with Lewy bodies (DLB), autonomic phenomena such as OH are common and attributed to dysfunction of sympathetic, parasympathetic, and visceral autonomic neurons. However, apart from MSA, few reports have focused on the neuropathologic aspects in PD and DLB. Here we assessed IML degeneration as well as the fine myelinated fibers (FFs; maximum diameter less than 3 μm) considered to be preganglionic sympathetic nerve fibers derived from IML neurons in PD, DLB, MSA, and age-matched normal controls (NC).

Methods: We counted IML neurons and measured the diameter and number of myelinated fibers of the ventral root at the level of the 12th thoracic segment.

Results: Compared to NC, number of IML neurons and density of FF were significantly reduced in PD (53% and 67%), DLB (47% and 71%) and MSA (27% and 42%). Compared to combined group of PD and DLB without OH (OH-), IML neurons in combined group of PD and DLB with OH (OH+) were significantly reduced (77%). Compared to NC, FF densities in OH-, OH+ were significantly reduced (74% and 59%). The mean ratio of small to large myelinated fibers in OH+ (1.18), but not that in OH-(1.58), was significantly lower than that in NC (3.17).

Conclusions: We present neuropathological evidence that IML neurons and FFs in the ventral root are reduced in PD and DLB and that the reduction was more severe in the combined group of OH+ than in OH-.