NEW YORK (Reuters Health) - The age-related decline in plasma testosterone levels is similar in men with Parkinson's disease (PD) and in those with Alzheimer's disease (AD), researchers report. They say testosterone deficiency "may act as a 'second hit' to impair cognitive function in neurodegenerative disease."

"Testosterone deficiency, a treatable condition commonly seen in aging men, has been linked to PD and AD," Dr. M. S. Okun, of the University of Florida, Gainesville, and colleagues write in the February issue of Neurology. "In normal subjects, low testosterone levels are associated with cognitive and neuropsychiatric symptoms, yet the relationship between testosterone levels and cognitive function in PD and AD remains unclear."

The researchers determined the levels of plasma testosterone in men enrolled in a clinical registry of patients with PD and AD, and performed neuropsychological testing on those who consented.

Linear regression analysis demonstrated that testosterone levels decreased with age in both PD (p < 0.03) and AD patients (p < 0.07). The rate of decline was similar between the groups.

Lower testosterone levels were associated with poorer performance on Trails B Seconds (p < 0.02) in PD patients.

Dr. Okun and colleagues conclude that testosterone deficiency may be a co-morbid feature in men with PD and AD. "A larger prospective longitudinal study is needed to confirm our results and to clarify the role of testosterone in neurodegenerative diseases," they say.

Neurology 2004;62:411-413

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