Methamphetamine/amphetamine abuse and risk of Parkinson's disease in Utah: a population-based assessment.

BACKGROUND Despite widespread use of methamphetamine and other amphetamine-type stimulants (METH/AMPH), little is known about the long-term medical consequences of METH/AMPH abuse and dependence. Preclinical neurotoxicity findings raise public health concerns that these stimulants may damage dopamine neurons, resulting in dopamine-related disorders such as Parkinson's disease (PD). METHODS A retrospective design was used to examine statewide medical records (1996 through 2011) linked to the Utah Population Database. Individuals 30 years or older on December 31, 2011 were assigned to a METH/AMPH cohort (ICD-9-CM 304.4, 305.7, 969.7, E854.2; N=4935), a cocaine cohort (ICD-9-CM 304.2, 305.6, 968.5, E855.2; N=1867) or a population cohort unexposed to drugs or alcohol for control selection. A competing-risks, proportional hazards model was used to determine whether the METH/AMPH or cocaine cohorts were at increased risk of developing PD (ICD-9-CM 332.0) or PD/parkinsonism/essential tremor (PD/PT; ICD-9-CM 332.0, 332.1, 333.0, 333.1) compared to individually sex- and age-matched controls (5:1 control to case ratio; N=34,010). RESULTS In METH/AMPH users, we observed an increased risk of PD and PD/PT (HRPD=2.8, 95%CI 1.6-4.8, P<10(-3); HRPD/PT=3.1, 95%CI 1.9-4.9, P<10(-4)) compared to population-based controls. Conversely, cocaine users exhibited no elevated risk of PD compared to controls. CONCLUSIONS We observed a near three-fold increased risk of PD in METH/AMPH users vs. controls which confirms prior observations and supports that PD risk in users may be higher than previous estimates. A suggestion that female and male users may differ in PD susceptibility warrants further study.