LETTERS TO THE EDITOR Treatment of Outlet Obstruction Constipation in Parkinson’s Disease With Botulinum Neurotoxin A

TO THE EDITOR: In addition to motor signs, patients with Parkinson’s disease (PD) suffer from a variable degree of autonomic impairment. Constipation is one of the most common autonomic dysfunctions observed in PD and may precede the onset of motor signs by many years (1). Chronic constipation, defined as the occurrence of less than three bowel movements per week accompanied by straining at stool, may be due to either slow transit or to outlet obstruction, and in PD both causes usually coexist (2). It is still unclear how many constipated PD patients have slow transit, outlet obstruction, or a combination of the two. Outlet obstruction is associated with a failure of relaxation, or even with a paradoxical contraction of the puborectalis muscle during straining, accentuating the flap-valve action of the anorectal angle and resulting in an obstruction to the onward passage of stool. Surgical treatments aimed at weakening or dilating the puborectalis muscle are often unsuccessful (3), whereas injections of botulinum toxin directly into the puborectalis muscle have provided promising results (4). In a PD patient with prominent signs of outlet obstruction–type constipation, we observed a dramatic improvement after injections of botulinum neurotoxin directly into the puborectalis muscle (5). This prompted us to perform a prospective study in PD patients with chronic constipation, to identify possible candidates for this treatment. PD outpatients seen at the movement disorders clinic filled an inventory of GI function (evaluating the number of bowel movements and defecatory function) and received a proctological evaluation. A total of 138 patients met the inclusion criteria for chronic constipation; 18 of them (13%) had isolated or prominent outlet-type constipation. Ten patients (one woman and nine men, mean age [ SD] 69.1 9.2 yr, mean duration of PD 70 53 months, mean duration of constipation 35.3 11 months) were studied. All the patients were treated with levodopa, dopamine agonists, and domperidone. They were evaluated by means of manometry, defecography, and electromyography before treatment and twice at monthly intervals after the injection. Botulinum neurotoxin (Botox, Allergan, Irvine, CA) was injected in the puborectalis muscle (two sites on either side of the muscle) under transrectal ultrasonographic guidance; the total dose per session was 100 U in each patient.