Subsequent Risks of Parkinson Disease in Patients with Autoimmune and Related Disorders: A Nationwide Epidemiological Study from Sweden

<i>Objectives:</i> To investigate associations between autoimmune disorders and Parkinson disease (PD), and to study whether the risk is associated with follow-up time and age. <i>Methods:</i> Standardized incidence ratios (SIRs) were calculated for PD in patients with autoimmune disorders by comparing them to subjects without autoimmune disorders. <i>Results:</i> Among 310,522 patients with a total of 33 conditions of autoimmune disorders, 932 patients developed subsequent PD, giving an overall SIR of 1.33 and 1.19 for PD diagnosed later than 1 year after follow-up. Six types of autoimmune disorders showed an increased risk. These conditions included: amyotrophic lateral sclerosis, Graves’s disease/hyperthyroidism, Hashimoto’s disease/hypothyroidism, multiple sclerosis, pernicious anemia, and polymyalgia rheumatica. The risks depended on the age at hospitalization for PD. <i>Conclusions:</i> A 33% overall excess risk of PD was noted among patients with an autoimmune disorder; the risk was increased during the first 10 years of follow-up after hospitalization of autoimmune disorders.