The Effect of a Low Dose of Intrathecal Morphine on Impaired Micturition Reflexes in Human Subjects with Spinal Cord Lesions

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Abstract
The potential therapeutic value of a low dose (200–250 μg) of intrathecal (i.t.) morphine on bladder capacity was tested in six subjects with chronic suprasacral spinal cord lesions. Micturition reflexes were examined by saline fill cystometry accompanied by EMG recordings from the external anal and urethral sphincters and selected lower limb muscles. Hyperactive detrusor reflexes were associated with a low capacity bladder in five of the six subjects. All subjects revealed vesicoexternal sphincter dyssynergia, and vesical-induced and spontaneous contractions of the abdominal and lower limb musculature. The result was incontinence and frequent catheterizations. Within 5–15 min of the bolus morphine injection into the L1–2 i.t. space, bladder capacity increased to near-maximal values in all subjects. Soon thereafter, uninhibited detrusor contractions, spontaneous motor discharges, and vesicosomatic (limb) reactions were abolished. A peak effect was observed within 2–4 h. Alterations of bladder capacity persisted for 18–22 h. Side effects included pruritus and nausea. Intrathecal morphine acts at sacral spinal cord sites, e.g., primary afferents and/or dorsal horn neurons, mediating vesicovesical and vesicosomatic (sphincter, limb) reflexes, and spontaneous motor discharges. Clinically, i.t. morphine may be an effective therapy for individuals with suprasacral spinal cord lesions when a low capacity bladder interferes with their quality of life.