In consultation with Clare Fowler, Department of Uro-Neurology, National Hospital for Neurology and Neurosurgery, UCLH NHS Hospitals and Institute of Neurology, London, UK

BLADDER PROBLEMS AND MULTIPLE SCLEROSIS

The spinal cord plays a central role in bladder dysfunction in MS. When MS damages the myelin, messages between the brain and the section of the spinal cord that controls the bladder can be interrupted, resulting in bladder problems.

The areas of the central nervous system that control the urinary system are situated in the lower part of the brain and the lower part of the spinal cord. Messages are transmitted between the brain and the urinary system along the nerves that make up the spinal cord (Figure 1). In a normally functioning urinary system, the brain receives a message that the bladder is full. The brain then replies to this sensation, when the social circumstances are suitable, by sending a message down the spinal cord, to the area that controls bladder functioning. The message tells the muscle in the bladder wall, called the detrusor, to contract at the same time as the muscle at the outlet of the bladder, called the sphincter, relaxes. This co-ordination between the muscles allows urine to be expelled from the bladder. As the figures show, the spinal cord is critical for making the connections between the brain and urinary system.

There are two major types of urinary malfunction that commonly occur in MS – failure of storage and failure of emptying. It is not known why some people experience one disorder and not the other, or why some individuals experience a combination of both.

Failure of storage occurs when an interruption of the spinal connecting pathway transmits messages that cause involuntary bladder contractions. This is known as an ‘over-active’ bladder and results in the person feeling the need to urinate frequently, but only in small amounts. Also people with an over-active bladder may experience urgency. If this is severe, the individual may also experience urge incontinence – a leakage of urine by involuntary detrusor muscle contraction together with a strong urge to urinate.

The other type of malfunction in the urinary system relates to inadequate emptying of the bladder. Instead of a co-ordinated activity between the important muscles, the sphincter (bladder outlet) does not relax when the detrusor (bladder wall) contracts so that urine flow is poor and interrupted, making bladder emptying incomplete.