Sexual Function in Parkinson's Disease
by Thomas Keeler, MD
At one time or another, people with Parkinson's, may have to address issues relating to sexual function on. In particular, erectile dysfunction has become a topic of much discussion in the general public over the past five years. We are exposed to ads, commentary, and medical experts in the media on a regular basis. In many ways, this is helpful for some patients because it can stimulate an open discussion that commonly, in years past, would have been more difficult to initiate with their physician.
Parkinson's disease and more severe neural dysfunction such as multiple systems atrophy (MSA) are commonly associated with sexual dysfunction. Quality of life studies have documented sexual dysfunction at rates approaching 60% to 80% in men and women with Parkinson's disease. Older people have higher rates than younger people. Young patients report rates in the 30% range, and this compares to healthy populations of younger individuals reporting 3% to 15% rates of sexual dysfunction.
Clearly, age and other medical conditions such as diabetes, hypertension, arterial sclerosis, and depression play major roles in causing sexual dysfunction. The neurologic control of erectile function in men involves two major pathways. A peripheral sensory mediated pathway involving penile nerves and a spinal cord reflex is mediated by local stimulation such as touch and vibration. The second pathway is located in the central nervous system (brain) and is controlled by several brain regions including the cerebral cortex, hypothalamus, and brainstem. The central brain regions appear to be under dopamine control as well as other neurotransmitters.
One experimental study inducing damage to the substantia nigra, an area known to malfunction in Parkinson's disease, resulted in changes in erectile function. Parkinson patients may well have erectile dysfunction as a result of damage to central dopamine pathways. Their peripheral pathways, however, remain intact. Female patients have a similar, centrally controlled pathway. Their peripheral pathways are less well understood.
Patients with Parkinson's disease and sexual dysfunction should discuss their problems with their primary care physician or their neurologist. Referral for evaluation by a specialist, such as a urologist or gynecologist, is commonly recommended. Other causes of sexual dysfunction should be identified, if present, and addressed. Male testosterone levels are usually assessed and corrected if necessary. Cofactors such as cigarettes, alcohol, and certain drugs or medications may need to be modified or eliminated. Women may benefit from estrogen replacement, either topically (in the form of a cream) or systemically.
Particularly important in Parkinson's disease patients are sedentary lifestyle and depression. Staying physically active with exercise is helpful to maintain cardiovascular integrity and a sense of well-being. Depression, when aggressively treated and corrected, may help resolve many sexual problems in both men and women.
One of the most significant advances in the treatment of male erectile dysfunction has been the introduction of a class of medications called phosphodiesterase (PDE) inhibitors. PDE is an enzyme found in most areas of the body and helps regulate intracellular events. PDE comes in at least 11 different variations. PDE-5 has been determined to be highly concentrated in penile tissues as well as clitoral and vaginal tissues. By blocking this enzyme, an increase in blood flow will occur, thus improving the quality of an erection.
Currently, there are three PDE-5 inhibitors available; sildenafil (Viagra), vardenafil (Levitra), and tadalafil (Cialis). All three medications have been effective in the treatment of erectile dysfunction and, with a few variations in their side effects, are safe and well tolerated. Caution must be taken in patients with Parkinson's disease who have autonomic nerve dysfunction or multiple system atrophy because these medications can and will cause a lowering of blood pressure. This could result in dizziness or fainting. Patients with these conditions should have their initial dosing at the doctor's office so that blood pressure effects can be assessed. To date, female sexual dysfunction has not been found to respond as dramatically to these medications, however medications continue to be studied.
Not all men respond to PDE-5 inhibitors or they may not tolerate certain side effects. Other forms of therapy are still available. Oral medications such as yohimbine and trazodone have shown some success. Apomorphine, which stimulates central dopamine receptors, is under study and has yet to receive FDA approval for erectile dysfunction.
Injectable therapies with alprostadil (Caverject) or other medications are effective but require direct injection of medication into the penis. Topical medications are also being studied. MUSE is available in the form of a topical urethral pellet (inserted into the penis). Lastly, mechanical intervention with a vacuum device or a surgically placed penile prosthesis may be right for some patients.
In summary, evaluation and treatment of sexual dysfunction in patients with Parkinson's disease has been shown to effectively improve quality of life scores and reduce depression indices. Treatment for men is generally well tolerated and effective. Available treatments for women remain elusive and continue to be under study.
Dr. Keeler is a urologist at Evanston Northwestern Healthcare in Illinois and is Assistant Professor of Clinical Urology, Department of Urology, Feinberg School of Medicine, Northwestern University