Beneficial Effects of Testosterone Replacement for the Nonmotor Symptoms of Parkinson Disease

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Abstract
TESTOSTERONE levels decline with normal aging, even in healthy men. Although the rate of decline can vary between individuals, both cross-sectional and longitudinal studies have confirmed this decline.1-3 Some older men (20% or more depending on age) will experience a decline in testosterone levels to the extent that they will develop symptoms of testosterone deficiency, such as decreased libido, lack of energy, fatigability, and depression.4 We recently found that similar to the general population, a large proportion of patients with Parkinson Disease (PD) in our registry had low levels of testosterone.5 Although it has long been known that treatment of low testosterone levels can improve deficiency symptoms in men, it has not been previously appreciated that the nonmotor symptoms in PD may also respond to replacement therapy. In a small sample of patients with low testosterone levels, we observed that some of the refractory nonmotor symptoms of PD did respond to testosterone replacement therapy.5 In this pilot study, we aimed to investigate further the effects of testosterone replacement on testosterone deficiency symptoms, cognitive and emotional function, as well as the motor and nonmotor symptoms of PD.