Ask the Doctor: Why do I keep needing the toilet in the night?

Frequent night-time urination could indicate either an overactive bladder or nocturnal polyuria. Photo / 123RF

Dr James Le Fanu answers reader questions. This week, is an overactive bladder diagnosis correct, or could there be something else at play?

Q. For some time I have had to get up several times at night to pass prodigious volumes of urine – despite hardly drinking at all for several hours before bedtime. Luckily I don’t have much difficulty in getting back to sleep but, when I do, I am often plagued by vivid dreams of desperately seeking a ladies’ toilet. I have been told I have an overactive bladder but, despite taking the drugs prescribed, my nocturnal perambulations continue tiresomely as before.

A. Of those on the wrong side of 60, most will be woken once or twice a night by the need to pass urine, which must thus be considered “normal”. More frequently than this and these “nocturnal perambulations” acquire the status of the medical symptom nocturia. The two possible explanations are either an “overactive bladder” or “nocturnal polyuria” that should be readily distinguished by any competent doctor – if not, as in this query, by the characteristic nature of the symptoms.

The ‘overactive’ bladder

The bladder is a compliant balloon which, when filled to capacity with 500ml of urine, initiates a neurological reflex causing the muscles in the wall to contract while simultaneously relaxing those around its opening – allowing for the free flow of urine. Rather than this (truly marvellous) synchronised process, the muscles in those with an overactive bladder contract spontaneously, resulting in the frequent passing of small amounts of urine (frequency) and the urgent need to do so. This can be corrected by drugs such as oxybutynin that inhibit the nervous impulses to the muscles of the bladder wall.

Nocturnal polyuria

The distinctive feature of this woman’s query is that she experiences frequency only at night, passing prodigious volumes every time. This nocturnal polyuria, as it is known, arises from reduced secretion of one of several hormones that ensure the constancy of the fluid content of the body – without which the tissues would become waterlogged or dehydrated. This antidiuretic hormone (ADH) secreted by the pituitary gland at the base of the brain reduces, as its name suggests, “diuresis” – the production of urine by the kidneys. Its secretion over a 24-hour period is strongly influenced by sleep, thus markedly reducing the volume of urine at night. Nocturnal polyuria, then, is an age-related disturbance of that cyclical rhythm for which there are two possible remedies.

Desmopressin

Desmopressin has the same chemical structure as the hormone ADH and can be taken either as a tablet or a nasal spray. “It has revolutionised my life,” writes one woman. “I now only have to visit the toilet once or twice a night, sometimes not at all. It seems rather odd that inhaling something up my nose should stop me peeing but I am immensely grateful that it does.”

Anti-inflammatory drugs

Desmopressin is not recommended for those with hypertension or other heart conditions as it can cause a rise in blood pressure. The unexpected efficacy of the alternative remedy – aspirin and similar anti-inflammatory drugs – was discovered fortuitously by family doctor Eric Lewis, as described in this column several years ago. “I have suffered from this annoying complaint for several years, passing up to one and a half litres of urine during four or five trips to the toilet,” he wrote. Until one evening he took a couple of aspirins to relieve some muscular pains and was astonished to wake the following morning to realise he had slept undisturbed throughout the night. His experience prompted a dozen similar anecdotal reports, subsequently investigated in a formal clinical trial with the anti-inflammatory drug diclofenac – confirming the merits of “this novel treatment option for a common condition”.