Nocturia is defined by the International Continence Society (ICS) as “the complaint that the individual has to wake at night one or more times for voiding (i.e. to urinate).” Its causes are varied and, in many patients, difficult to discern.
Diagnosing nocturia requires knowing the patient's nocturnal urine volume (NUV). The ICS defines NUV as “the total volume of urine passed between the time the individual goes to bed with the intention of sleeping and the time of waking with the intention of rising.” Thus, NUV excludes the last void before going to bed, but includes the first morning void if the urge to urinate woke the patient. Although not every patient needs treatment, most people seek treatment for severe nocturia, waking up to void more than 2-3 times per night. The amount of sleep a patient gets, and the amount they intend to get, are also considered in a diagnosis. The term is derived from Latin nox, night, and Greek [τα] ούρα, urine.
Two major hormones that regulate the body’s water level are arginine vasopressin (AVP) and atrial natriuretic hormone (ANH). AVP is an antidiuretic hormone produced in the hypothalamus and stored in and released from the posterior pituitary gland. AVP increases water absorption in the collecting duct systems of kidney nephrons, subsequently decreasing urine production. It is used to regulate hydration levels in the body. ANH, on the other hand, is released by cardiac muscle cells in response to high blood volume. When activated, ANH releases water, subsequently increasing urine production.
Nocturia has four major underlying causes: global polyuria, nocturnal polyuria, bladder storage disorders, or mixed cause. The first two processes are due to irregular levels of AVP or ANH. The third process is a vesical problem.
Global polyuria is the continuous overproduction of urine which is not only limited to sleep hours. Global polyuria occurs in response to increased fluid intake and is defined as urine outputs of greater than 40 mL/kg/24 hours. The common causes of global polyuria are primary thirst disorders such as diabetes mellitus and diabetes insipidus (DI). Urination imbalance may lead to polydipsia or excessive thirst to prevent circulatory collapse. Central DI is caused by low levels of AVP that helps regulates water levels. In nephrogenic DI, the kidneys do not respond properly to the normal amount of AVP.
Diagnosis of DI can be made by an overnight water deprivation test. This test requires the patient to eliminate fluid intake for a fixed period of time, usually around 8–12 hours. If the first morning void is not highly concentrated, the patient is diagnosed with DI. Central DI usually can be treated with a synthetic replacement of AVP, called desmopressin. Desmopressin is taken to control thirst and frequent urination. Although there is no substitute for nephrogenic DI, it may be treated with careful regulation of fluid intake.
Nocturnal polyuria is defined as an increase in urine production during the night but with a proportional decrease in daytime urine production that results in a normal 24-hour urine volume. With the 24-hour urine production within normal limits, nocturnal polyuria can be translated to having a nocturnal polyuria index (NPi) greater than 35% of the normal 24-hour urine volume. NPi is calculated simply by dividing NUV by the 24-hour urine volume. Similar to the inability of control urination, a disruption of arginine vasopressin (AVP) levels has been proposed for nocturia. Compared with the normal patients, nocturia patients have a nocturnal decrease in AVP level.
Other causes of nocturnal polyuria include diseases such as congestive heart failure, nephritic syndrome and liver failure; or lifestyle patterns such as excessive nighttime drinking. The increased airway resistance that is associated with obstructive sleep apnea may also lead to nocturnal polyuria. Obstructive sleep apnea sufferers have shown to have increases in renal sodium and water excretion that are mediated by elevated plasma ANH levels.
A bladder storage disorder is any factor that increases the frequency of small volume voids. These factors are usually related to lower urinary tract symptoms that affect the capacity of the bladder. Patients with nocturia who do not have either polyuria or nocturnal polyuria according to the above criteria most likely have a bladder storage disorder that reduces their nighttime voided volume or a sleep disorder. Nocturnal bladder capacity (NBC) is defined as the largest voided volume during the sleep period.
Decreased NBC can be traced to a decreased maximum voided volume or decreased bladder storage. Decreased NBC can be related to other disorders such as prostatic obstruction, neurogenic bladder dysfunction, learned voiding dysfunction, anxiety disorders, or certain pharmacological agents.
A significant number of nocturia cases occur from a combination of causes. Mixed nocturia is more common than many realize and is a combination of nocturnal polyuria and decreased NBC. In a study of 194 nocturia patients, 7% were determined to have simple nocturnal polyuria, 57% had decreased NBC, and 36% had a mixed cause of the two. The cause of nocturia is multifactorial and often unrelated to an underlying urological condition. Mixed nocturia is diagnosed through the maintenance and analysis of bladder diaries of the patient. Assessment of cause contributions are done through formulas.
As with any patient, a detailed history of the problem is required to establish what is normal for the patient and what isn’t. The principal diagnostic tool for nocturia is the voiding bladder diary. Based on information recorded in the diary, a physician can classify the patient as having polyuria, nocturnal polyuria, or bladder storage problems. Timing of voids, number of voids, and volume of urine voided should be recorded in the diary. Volume of fluid intake and time of intake should also be recorded. Patients should include the first morning void in the NUV, however, the first morning void is not included with the number of nightly voids.
Although there is no cure for nocturia, there are many actions people can take to manage their symptoms. Prohibiting the intake of caffeine and alcohol has helped some individuals with the disorder. Compression stockings may be worn through the day to prevent fluid from accumulating in the legs, unless heart failure or another contraindication is present. Drugs that increase the passing of urine can help decrease the third spacing of fluid, but they could also increase nocturia.
A common action patients take is to not consume any fluids in the hours before bedtime, which especially helps people with urgency incontinence. However, a study on this showed that it reduced voiding at night by only a small amount and is not ideal for managing nocturia in older people.
For people suffering from nocturnal polyuria, this action does not help at all because of irregular AVP levels and the inability to respond with the inhibition of increased voiding. Fluid restriction also does not help people who have nocturia due to gravity-induced third spacing of fluid because fluid is mobilized when they lie in a reclining position.
If the cause of nocturia is related to the obstruction of the prostate or an overactive bladder, surgical actions may be sought out. Transurethral prostatectomy/incision of the prostate and surgical correction of the pelvic organ prolapse, sacral nerve stimulation, clam cystoplasty, and detrusor myectomy are both treatment options and can help alleviate the symptoms of nocturia.
Desmopressin has some benefit in adults who have problems with night time urination. It is FDA approved for this indication since 2017. One negative effect seen is dilutional hyponatremia. Using this treatment in older patients and people at risk for hyponatremia means having to monitor the serum sodium concentration because there are severe risks if the concentration falls.
Other drugs that are often used to treat nocturia include oxybutynin, tolterodine, solifenacin, and other antimuscarinic agents. These drugs are especially used in patients who suffer from nocturia due to an overactive bladder and urgency incontinence because they help bladder contractility.
Although nocturia is little-known to the general public, some research suggests that more than 60% of people are negatively affected by it. The resulting insomnia and sleep deprivation can cause exhaustion, changes in mood, sleepiness, impaired productivity, fatigue, increased risk of accidents, and cognitive dysfunction. 25% of falls that older individuals experience happen during the night, of which 25% occur while waking up to void.
A quality of life test for people who experience nocturia was published in 2004. The pilot study was conducted only on men.
Studies show that 5-15% of people who are 20–50 years old, 20-30% of people who are 50–70 years old, and 10-50% of people 70+ years old, urinate at least twice a night. Nocturia becomes more common with age. More than 50 percent of men and women over the age of 60 have been measured to have nocturia in many communities. Even more over the age of 80 are shown to experience symptoms of nocturia nightly. Nocturia symptoms also often worsen with age. Although nocturia rates are about the same for both genders, data shows that there is a higher prevalence in younger women than younger men and older men than older women.
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