RESEARCH PROFILES

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Intravesical Capsaicin for Treatment of Neurogenic Bladder

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By Anita Shama
Canadian Spinal Research Organization

The main control center for bladder function is the brain. It enables voiding to take place at low pressure by causing the detrusor muscle in the bladder to contract and the sphincter muscle to relax. There are also nerves which extend from the sacral part of the spinal cord that activate the detrusor muscle. These sensory nerves send information from the bladder to the spinal cord telling it when the bladder is full or in pain.

After a SCI the bladder is no longer controlled by the brain. The sacral nerves cause the bladder to become spastic, also known as detrusor hyperreflexia, at low volumes of urine. Since the sphincter muscle is no longer able to relax, the bladder pressure increases leading to renal failure and eventually death if left untreated.

CAPSAICIN is a neurotoxin found in hot peppers. It has the ability to block sensory nerves involved in bladder spasticity. It does this by binding to receptor sites on the nerve fibres. This leads to depolarization of the nerves causing them to release neuropeptides from their terminals. Initially, the nerves are excited but the neuropeptides are quickly depleted and the nerves are desensitized.

The effect is long term since blockage of the main transport of the neurotrophic factor causes a reduction in neuropeptide production. For persons experiencing hyperreflexia, this causes an increase in their bladder capacity and lowers the pressure in their bladder making them less prone to kidney damage.

The objectives of a study currently being conducted on capsaicin are:

1. To reduce the detrusor leak point pressure (DLPP), which is the bladder urine storage pressure tobelow 40 cm H20. To increase the bladder capacity to above 250 ml. To decrease the urgency of urination, detrusor hyperreflexia, and autonomic dysreflexia.
2. To reduce or eliminate incontinence.

Capsaicin is injected into the bladder through a catheter and held for 1 hour. The dosage varies between patients depending on their degree of bladder control. Side effects may include autonomic dysreflexia or supra pubic pain for a few minutes during time of injection.

The future aim is to eventually be able to predict the dosage of capsaicin, ditropan, and IC required to control bladder pressure.