Parkinson Disease and Melanoma: Confirming and Reexamining an Association.

OBJECTIVE To examine an association between melanoma and Parkinson disease (PD). PATIENTS AND METHODS Phase I: Rochester Epidemiology Project records were used to identify (between January 1, 1976, and December 31, 2013) patients with PD in Olmsted County, Minnesota, with 3 matched controls per case. After review, JMP statistical software with logistic regression analysis was used to assess the risk of preexisting melanoma in patients with PD vs controls. Phase II: All Rochester Epidemiology Project cases of melanoma were identified (between January 1, 1976, and December 31, 2014), with 1 control per case. A Cox proportional hazards model was used to assess the risk of developing PD after the index date in cases vs controls, and Kaplan-Meier analysis was performed to determine the 35-year cumulative risk of PD. A Cox proportional hazards model was used to assess the risk of death from metastatic melanoma in patients with melanoma without PD compared with those with PD. RESULTS Phase I: Patients with PD had a 3.8-fold increased likelihood of having preexisting melanoma as compared with controls (95% CI, 2.1-6.8; P<.001). Phase II: Patients with melanoma had a 4.2-fold increased risk of developing PD (95% CI, 2.0-8.8; P<.001). Kaplan-Meier analysis revealed an increased 35-year cumulative risk of PD in patients with melanoma (11.8%) compared with controls (2.6%) (P<.001). Patients with melanoma without PD had a 10.5-fold increased relative risk of death from metastatic melanoma compared with patients with melanoma with PD (95% CI, 1.5-72.2) (P=.02). CONCLUSION There appears to be an association between melanoma and PD. Further study is warranted; but on the basis of these results, physicians may consider counseling patients with melanoma about PD risk and implementing cutaneous and ocular melanoma surveillance in patients with PD.