Accumulating evidence indicating that inflammatory responses play crucial roles in
Parkinson's disease (PD) development provided a hypothesis that physiological alpha-synuclein
may contribute to inflammatory responses against infections during non-advanced stages
of PD. Thus, we examined the risk of catching a common cold in patients with PD as
compared to other common brain diseases.
We extracted PD (non-advanced; without dementia) and control (AD: Alzheimer's disease,
migraine, epilepsy, and ischemic stroke) patient data from insurance claim data available
between 2010 and 2021. After confirming the clinical PD diagnosis, we investigated
factors associated with cold diagnoses and used propensity score matching to identify
differences in the incidence of colds between PD and control patients.
Diagnosis of colds in PD patients (n = 726) and controls (AD = 377, migraine = 1019,
epilepsy = 3414, ischemic stroke = 6943) was found in 1186 (9.5%) patients, which
was independently associated with being female (odds ratio: OR 1.59; 95%CI 1.41–1.79;
P < 0.0001), follow-up by neurologists (OR 1.30; 95%CI 1.15–1.48; P < 0.0001), diagnosis of PD (OR 0.30; 95%CI 0.20–0.45; P < 0.0001) and COVID-19 pandemic period (OR 0.58; 95%CI 0.47–0.72; P < 0.0001). After propensity score matching, the incidence of colds was significantly
lower in PD (3.4%) versus in controls; AD (9.8%; P < 0.0001), migraine (13.3%; P < 0.0001), epilepsy (11.0%; P < 0.0001), ischemic stroke (8.8%; P < 0.0001).
Patients with PD were less likely to be diagnosed with colds. However, several confounding
factors will need to be examined. Moreover, alpha-synuclein may provide protective
resistance to viral infections by activating the immune system due to chronic inflammation
in non-advanced PD patients.