Increased risk of Parkinson's disease in individuals hospitalized with conditions related to the use of methamphetamine or other amphetamine-type drugs

Background: Since methamphetamine and other amphetamine-type stimulants (meth/amphetamine) can damage dopaminergic neurons, researchers have long speculated that these drugs may predispose users to develop Parkinson's disease (PD), a dopamine deficiency neurological disorder. Methods: We employed a retrospective population-based cohort study using all linked statewide California inpatient hospital episodes and death records from January 1, 1990 through December 31, 2005. Patients at least 30 years of age were followed for up to 16 years. Competing risks analysis was used to determine whether the meth/amphetamine cohort had elevated risk of developing PD (ICD-9 332.0; ICD-10 G20) in comparison to a matched population-proxy appendicitis group and a matched cocaine drug control group. Individuals admitted to hospital with meth/amphetamine-related conditions (n = 40,472; ICD-9 codes 304.4, 305.7, 969.7, E854.2) were matched on age, race, sex, date of index admission, and patterns of hospital admission with patients with appendicitis conditions (n = 207,831; ICD-9 codes 540-542) and also individuals with cocaine-use disorders (n = 35,335; ICD-9 codes 304.2, 305.6, 968.5). Results: The meth/amphetamine cohort showed increased risk of PD compared to both that of the matched appendicitis group [hazard ratio (HR) = 1.76, 95% CI: 1.12-2.75, p = 0.017] and the matched cocaine group [HR = 2.44, 95% CI: 1.32-4.41, p = 0.004]. The cocaine group did not show elevated hazard of PD compared to the matched appendicitis group [HR = 1.04, 95% CI: 0.56-1.93, p = 0.80]. Conclusion: These data provide evidence that meth/amphetamine users have above-normal risk for developing PD.