Epidemiology of Parkinson's Disease: A Population-Based Study in Primary Care in Italy

Background: There are no studies on prevalence, incidence and comorbidities of Parkinson's disease (PD) in the Italian population. Methods: The database of 700 Italian general practitioners (population, 923,356) was investigated. All patients with International Classification of Diseases Ninth Revision - Clinical Modification (ICD-9-CM) diagnosis of PD during the period 2002-2012 were included. Parkinsonisms were excluded. Clinical conditions preceding PD were identified through ICD-9-CM codes. The Charlson Comorbidity Index was used. PD crude and standardized prevalence and annual incidence were calculated. Crude and adjusted hazard ratios were calculated for comorbidities. Results: A total of 2,204 patients (1,140 men, 1,064 women, age 22-95 years) were included. The crude prevalence of PD was 239/100,000. Prevalence increased exponentially with age. Standardized prevalence was 233 (95% CI 232-235). One hundred ninety-four patients were newly diagnosed, giving a crude incidence of 22/100,000 and a standardized incidence of 23.1/100,000 (95% CI 22.9-23.2). Incidence increased steadily until age 75-84 years and then decreased. Older age, cardiovascular and gastrointestinal disorders, diabetes, and restless-legs syndrome were associated with increased PD risk and smoking and hypersomnia with decreased PD risk. The Charlson Comorbidity Index was associated with PD risk with a documented gradient. Conclusions: Prevalence and incidence of PD in Italy are in line with studies with the highest case ascertainment. PD risk varies with the number and type of comorbidities.