Though PD patients rarely complain of sexual difficulties, if specifically asked, dysfunction in this area is very common. Bronner et al. (65) performed a comprehensive assessment of sexuality in 75 patients (32 women, 43 men) with PD who did not complain of problems in this area. Using specific sexual function scales, they asked patients to rate their sexuality currently and retrospectively before the onset of their PD. They found that in men, 68% had erectile dysfunction, 65% were dissatisfied with their sexual life, and 40% had difficulty reaching orgasm. In women, the major problems were difficulty getting aroused (88%), difficulty reaching orgasm (75%), and decreased sexual desire (47%). Comparing scores before PD onset to the present, most patients reported a deterioration in sexual functioning with the progression of PD. Using stepwise regression, the authors found that in men, associated disease, medications, and severity of PD predicted sexual dysfunction, whereas in women, levodopa use appeared to decrease sexual desire.
The underlying neuroanatomical substrate for sexual dysfunction in PD is complex and poorly understood. The central dopaminergic system is known to be important for sexual functioning, but conflicting data exist on whether dopaminergic drugs have a beneficial or harmful effect on sexual performance. Erectile dysfunction in men is probably due mainly to autonomic degeneration with the progression of PD.
Treatment of the many facets of sexual dysfunction in PD is complex, and most recommend that special attention be given to ascertaining this problem (since patients will rarely volunteer it during a routine visit) and that sexual counseling be offered to those in whom problems are identified. Erectile dysfunction in men has received specific attention in the literature, and several drugs have been tested as therapeutic agents for this problem. Sublingual apomorphine, a potent D1- and
D2-dopamine agonist, has been studied in a rigorous clinical trial and found to be effective at improving erectile dysfunction due to several different etiologies, although it has not been specifically studied in PD patients (66). Sublingual apo-morphine is not available in the United States. The dopamine agonist pergolide has been found to improve sexual function in PD patients, presumably also via a central dopaminergic mechanism (67).
Several studies have evaluated the effects of sildenafil in PD patients with erectile dysfunction. An open-label pilot study (68) showed that in 10 men, sildenafil improved sexual satisfaction, erectile function, and the ability to reach orgasm. In a larger open-label study (69) of 33 depressed male PD patients given a fixed dose of 50 mg of sildenafil one hour before sexual activity, 84.8% reported improved erections. A double-blind, placebo-controlled crossover study compared the efficacy and adverse effects of sildenafil in 12 patients with PD to 12 patients with MSA (70). Using the international index of erectile dysfunction as the primary efficacy parameter, they found that 9 of 10 PD patients completing the study had improved erectile function when assigned to active drug. There was a slight but asymptomatic decline in mean blood pressure measurements one hour after active drug ingestion in the PD patients. In contrast, although the MSA patients had improved erectile function on active drug, severe, symptomatic orthostatic declines in blood pressure were seen in three patients one hour after ingestion of the active drug, leading to discontinuation of recruitment of MSA patients into the study.
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