Cutaneous sensory and autonomic denervation in progressive supranuclear palsy

Progressive Supranuclear Palsy (PSP) is a progressive neurodegenerative tauopathy characterised by motor, behavioural and cognitive dysfunction. While in the last decade, sensory and autonomic disturbances as well as peripheral nerve involvement are well-recognised in Parkinson's Disease (PD), little is known in this regard for PSP. Herein, we aim to assess peripheral sensory and autonomic nerve involvement in PSP and to characterise possible differences in morpho-functional pattern compared to PD patients.

We studied 27 PSP and 33 PD patients without electrophysiological signs of neuropathy, and 33 healthy controls (HC). In addition to motor impairment, evaluated by means of UPDRS-III and the PSP rating scale, all patients underwent clinical, functional and morphological assessment of sensory-autonomic nerves through dedicated questionnaires, sympathetic skin response, dynamic sweat test and skin biopsies. The analysis of cutaneous sensory and autonomic innervation was performed using indirect immunofluorescence and confocal microscopy.

PSP patients displayed a length-dependent loss of sensory and autonomic nerve fibres associated with functional impairment compared to HC and, overall, a more severe picture than in PD patients. The disease severity correlated with the loss of intraepidermal nerve fibre density in the leg of PSP patients (p < 0.05).

We demonstrated a length-dependent small fibre pathology in PSP, more severe compared to PD, and paralleling disease severity. Our findings suggest the morphological and functional study of cutaneous nerves as possible biomarkers to monitor disease progression and response to new treatments.