Ten-Second Cold Water Stress Test Differentiates Parkinson’s Disease from Multiple System Atrophy: A Cross-Sectional Pilot Study

<b>Background/Objectives</b>: Patients with Parkinson's disease (PD) often have cold hands and experience frostbite. The diagnostic criteria for multiple system atrophy (MSA) also describe cold and discolored hands; however, in our clinical experience, the hands are relatively warm. These symptoms are thought to be caused by autonomic dysfunction; however, the detailed mechanisms and differences in cold hands between MSA and PD remain unclear. We aimed to identify an appropriate cold stimulation test to differentiate patients with PD and MSA using finger surface temperature (FST). <b>Methods</b>: We included a total of 34 patients, 27 with PD and 7 with MSA diagnosed at least 5 years after disease onset. After 15 min in a room with constant temperature and humidity, the patient's hand was placed in cold water at 4 °C for 10 s as the cold water stress test (10sec-CWST). FST was captured using a thermal imaging camera every minute for 15 min, and the recovery of FST was analyzed. The association between the clinical characteristics of each patient and the degree of FST recovery was examined. <b>Results</b>: All patients completed the 10sec-CWST without adverse events. Patients with PD showed a significantly slower recovery of FST after 7 min compared to those with MSA, with a maximum difference at 11 min (PD: 8.1 ± 0.6 °C; MSA: 10.5 ± 0.3 °C; <i>p</i> < 0.01). FST recovery at 11 min was negatively correlated with the degree of resting hand tremor (r = -0.585, <i>p</i> < 0.01). <b>Conclusions</b>: FST after 10sec-CWST may be a safe and efficient test to differentiate PD and MSA.