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April 18, 2002


Low Testosterone and Parkinson's Disease in Males – Emory Researchers Study the Possibilities of a Common, Unrecognized Comorbidity

Emory University researchers may have found a common but heretofore unrecognized link between low testosterone levels and certain non-motor symptoms (fatigue, depression, anxiety or sexual dysfunction) in male Parkinson's disease (PD) patients. When given testosterone replacement therapy (TRT), the researchers report that patients with low levels of testosterone experienced significant improvement in these symptoms, which had not responded to other medications. But investigators caution they only looked at a small group of five patients and they did not compare those people to a placebo or control group.

Michael Okun, M.D., and Mahlon DeLong, M.D., in the Department of Neurology, as well as William McDonald, M.D., in the Department of Psychiatry and Behavioral Sciences will present their findings at the American Academy of Neurology 54th Annual Meeting in Denver, Colo., on April 17. The researchers will also publish their work in an upcoming issue of the Archives of Neurology.

"Testosterone deficiency affects 20 to 25 percent of males over age 60 in the general population and it turns out this deficiency may account for some of the non-motor symptoms seen in PD," says Dr. DeLong. "However, there have been no prior clinical studies on the effects of testosterone replacement in male PD patients." Emory researchers reviewed the cases of five male Parkinson's patients who came to their clinic with unexplained loss of energy and vitality. These patients were not responsive to anti-parkinsonian and anti-depressant medications and had no evidence of other conditions such as hypothyroidism. Researchers screened for testosterone deficiency with the St. Louis Testosterone Deficiency Questionnaire, a 10-point validated questionnaire to determine low testosterone levels. Blood plasma tests to check for low testosterone were also performed. The five patients then began testosterone replacement.

Okun and colleagues reported that following treatment, all five patients experienced significant improvement in refractory, or unresponsive, non-motor symptoms of PD, especially fatigue, depression, anxiety and decreased libido. Motor disabilities appeared to improve in several men, but researchers are unsure whether they improved secondarily as a result of increased energy or if they were directly affected by the TRT.

To assess the prevalence of testosterone deficiency in male PD patients, Emory researchers also analyzed testosterone levels in 68 PD patients enrolled in a Parkinson's registry at Emory. Researchers discovered 35 percent of male PD patients in the registry had low testosterone levels. The risk of testosterone deficiency was found to increase 2.8 fold per decade. These numbers at least parallel those seen in the general male geriatric population.

Dr. Okun comments, "More controlled studies are needed to verify the proportion of male PD patients found to have low testosterone." Further studies will also help determine whether testosterone deficiency is simply a comorbid condition (a medical condition that exists in addition to the main diagnosis) or if it may influence the onset, progression and clinical expression of the disease.

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