Journals publish letters sent to their editors to enlighten clinicians, students and others about unusual patient cases. The following story describes an atypical response to the medication, rasagiline. Prescribed for patients with PD, it is thought to harbor neuro- protective effects.
The sixty- five year old patient was born with spina bifida, but had no dysfunction of bowel, bladder, or sexual function. The patient received a diagnosis of PD at age sixty- one and took 2mg rasagiline to treat his symptoms. A month after initiating treatment with levodopa he experienced spontaneous ejaculation occurring in clusters, every ten minutes for thirty minutes. Such episodes happened every two to seven days. Ejaculation took place without an erection and with no stimulation. In between these episodes he had regular sexual activity with no autonomic problems.
On his neurological exam, the clinician found left- sided rigidity, and slowness of movement without a resting tremor. The dorsiflexors were mildly weak, and he had decreased proprioception of vibration in the toes of both feet. The lower body had decreased reflexes.
The episodes of spontaneous ejaculation continued even when the dose of rasagiline dropped by half, but stopped when he discontinued the drug. Without rasagiline, the patient noted his symptoms worsened, and his clinician subsequently prescribed a four-month course of 10 mg of selegiline daily, to counteract additional movement concerns. After a period of four months, without sexual side effects, the patient began rasagiline anew, at 2 mg per day. Within a month spontaneous ejaculations re-occurred. The patient elected to stay on the medication, and still experiences unprompted orgasms. He also noted orgasms associated with planned sexual activity are more explosive, with less recovery time needed between such events.
Apart from hypersexuality, the prevalence and range of sexual dysfunction in those with PD, gets little attention. However, numerous reports of sexual problems occurring after the use of dopamine agonists, specifically apomorphine and ropinirole exist. This report, the authors believe, is the first of its kind.
Researchers noted dopamine’s role in inducing an erection when apomorphine was undergoing drug trials for the treatment of alcoholism. Apomorphine is a powerful dopamine receptor agonist and has been marketed as a treatment for human erectile dysfunction. Bromocriptine and ropinirole, two other dopamine agonists are reported to have improved erectile dysfunction, as well.
Experiencing ejaculation without an erection is curious. The author notes animal studies have shown dopamine aids ejaculation. For ejaculation to occur without an erection, different dopamine receptor sub types may come into play, as stimulation of D2 receptors in the rat’s pre- optic area by the D2/D3 receptor agonist, quinelorane, promotes ejaculation. Piribedil, another D2 and D3 receptor agonist significantly increases rat ejaculation with less effect on erection. Further support that D3 receptors in the brain modulate orgasm and the period between ejaculations, appeared when technicians injected a selective D3 receptor antagonist into the medial pre- optic area of the rat brain, abolishing ejaculations without affecting erections. It is also possible rasagiline increases central dopamine at either the brainstem or medial pre- optic area to increase signals to the spinal cord ejaculation center. The author concedes the patient is unique due to his underlying spina bifida, suggesting spinal cord or peripheral involvement is responsible for the aberrant reaction to rasagiline. As neurologists inquire more frequently into the sexual function of their patients, and with increasing use of rasagiline, more instances of the unusual side effect should occur.
Chuang R.S. and Lang A.E. Letters to the Editor Rasagiline- Induced Spontaneous Ejaculation. Movemnt. Dis. V.24 I.14 Oct. 30, 2009.