BACKGROUND AND OBJECTIVES: Although widely described in Parkinson's disease (PD), peripheral neuropathy (PNP) is scarcely reported in progressive supranuclear palsy (PSP). We aimed to compare the frequency, clinical and electrophysiologic characteristics of PNP in PSP and PD patients. METHODS: This cross-sectional study included 23 PSP and 93 PD patients. Demographic data, Movement Disorders Society-Unified Parkinson's Disease Rating Scale-III (MDS-UPDRS-III), Hoehn-Yahr staging, Toronto Clinical Neuropathy Score, nerve conduction study (NCS), and sympathetic skin response (SSR) were recorded. Diagnosing isolated large fiber neuropathy required abnormal NCS. Isolated small fiber neuropathy required clinical findings of pinprick and thermal sensory loss and/or allodynia and/or hyperalgesia with/without impaired SSR, along with normal NCS. RESULTS: PNP was commoner in PSP than PD (65.2% vs. 50.5%, P = 0.21). While a comparable proportion in both groups had clinical neuropathy, NCS abnormalities predominated in PSP (65.2% vs. 39.8%, P = 0.03). All patients had distal symmetrical axonal polyneuropathy. A significantly higher proportion of PSP patients had large fiber involvement (65.21% vs. 39.78%, χ 2 = 4.82
P = 0.03) and mixed fiber PNP (60.9% vs. 33.3%, P = 0.01). PSP patients with neuropathy had a significantly shorter disease duration [median (interquartile range {IQR} = 2 (2-3) years vs. 6 (3-9) years, P <
0.001], higher MDS-UPDRS-III score [median (IQR) = 47 (36-54) vs. 34 (28-49), P = 0.049], higher Hoehn-Yahr stage [median (IQR) = 4 (2-5) vs. 3 (1-5), P <
0.001], and shorter duration of levodopa use [median (IQR) = 2 (1-2) years vs. 3.5 (2-5) years, P = 0.006]. NCS parameters were comparable between PSP and PD patients with neuropathy. While PNP in PSP was not associated with any of the clinical variables, a longer disease duration was independently associated with PNP in PD. CONCLUSIONS: PNP affected two-thirds of PSP patients and was more prevalent than PD. Both groups had distal symmetrical axonal polyneuropathy, with mixed fiber PNP predominating in PSP. A longer disease duration in PD was associated with PNP.