Neurological Causes of Retention—A Word of Warning!
It is all too easy to assume that urinary retention in a man is due to BPH. Of course this is by far the commonest cause in elderly men, but in the younger man (below the age of 60, but even in some men older than 60), spend a few moments considering whether there might be some other cause. Similarly, in women,
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where retention is much less common than in men, think why the patient went into retention.
Be wary of the patient with a history of constipation and be particularly wary where there is associated back pain. We all get back pain from time to time, but pain of neurological origin, such as that due to a spinal tumour or due to cauda equina compression from a prolapsed intervertebral disc (pressing on S2-S4 nerve roots, thereby impairing bladder contraction) may be severe, relentless, and progressive. The patient may say that the pain has become severe in the weeks before the episode of retention. Nighttime back pain and sciatica (pain shooting down the back of the thigh and legs), which are relieved by sitting in a chair or by pacing around the bedroom at night, are typical of the pain caused by a neurofibroma or ependymoma affecting the cauda equina. Interscapular back pain is typically caused by tumours that have metastasized to the thoracic spine.
Altered sensation due to a cauda equina compression can manifest as the inability to tell whether the bladder is full, inability to feel urine passing down their urethra while voiding, and difficulty in knowing whether one is going to pass faeces or flatus.
Male patients with a neurological cause for their retention (such as spinal tumour) may report symptoms of sexual dysfunction that may appear bizarre (and may therefore be dismissed). They might have lost the ability to get an erection or have lost the sensation of orgasm. They might complain of odd burning or tingling sensations in the perineum or penis.
It doesn't take more than a minute or two to ask a few relevant questions (Are you constipated? Have you had back pain? Do your legs feel funny or weak?), to establish whether the patient has a sensory-level sign (the cardinal sign of a cord compression) and other neurological signs and to test the integrity of the sacral nerve roots that subserve bladder function—S2 to S4. In the male patient, this can be done by squeezing the glans of the penis while performing a digital rectal examination (DRE). Contraction of the anus, felt by the physician's palpating finger, indicates that the afferent and efferent sacral nerves and the sacral cord are intact. This is the bulbocavernosus reflex (BCR). In women, once catheterised, the 'same' reflex can be elicited by gently tugging the catheter onto the bladder neck, again while doing a DRE. Again, contraction of the anus indicates that the afferent and efferent sacral nerves and the sacral cord are intact.