Enuresis

Investigation shows that enuresis is a heterogeneous disorder comprising many different subgroups.[7] The common principle is a mismatch between nocturnal urine production and nighttime functional bladder capacity compounded by an inability to wake, resulting in bedwetting. In some children, sleep-disordered breathing may compound the problem due to arousal thresholds while sleeping.

Disorders of sleep arousal

In the case of a child who seems to have normally concentrated urine and an unremarkable bladder capacity, a baseline disorder in arousal is a reasonable assumption.

Decreased functional bladder capacity

There tends to be normal urine concentration (measured by laboratory urine testing) and there may be a history of daytime frequency - a subconsciously learned coping behavior - only elucidated in the voiding diary.

Nocturnal polyuria

For patients who complain of nocturnal polyuria or of having their largest void of the day during the night, it is reasonable to assume that the etiology of their enuresis is related to nocturnal polyuria. Poorly concentrated urine as assessed by urinalysis can also be indicative of nocturnal polyuria.

Nocturnal overactive bladder

Children who do not respond to interventions with alarm therapy or desmopressin may suffer from overactive bladder. Often daytime symptoms are masked by moderating fluid intake to minimize daytime urination.

During daytime enuresis it is typical that the child defers voiding until incontinence occurs. This may be due to a reluctance to use the toilet as a result of social anxiety or a preoccupation with school or play activity. The events most commonly occur in the early afternoon on school days or after returning from school.[1]

Typically, a circadian rhythm of urine production develops early in childhood, resulting in a reduced nocturnal diuresis.[8] This is regulated by an increase in nocturnal release of arginine vasopressin (AVP) or antidiuretic hormone (ADH), or solute excretion.[9] A significant portion of children affected with enuresis have increased nocturnal urine volume and, specifically, the urine volume is larger on nights when the patient has a wet episode.[10] This has led to various hypotheses on the mechanism of the increased nocturnal diuresis. The most historically studied theory revolves around a decrease in secretion of AVP, which leads to increased free-water excretion. In addition, some children have increased nighttime fluid consumption, which physiologically leads to increased nocturnal diuresis. The sum total is that increased nocturnal urine production means that avoiding enuresis depends on the functional capacity of the bladder and ultimately on the ability of the child to wake in time.

Another subgroup of nocturnal enuretics is composed of children who have normal nocturnal urine production but have reduced bladder capacity or bladder dysfunction.[11][12] These patients may either have normal daytime bladder function and normal urodynamics and bladder capacity, or have daytime abnormalities that remain occult.[13] The theory on why a child with normal daytime bladder function would develop abnormal behavior at night centers on a deficiency of inhibitory brainstem signaling, which can result in bladder instability only at night.[14] Any pathology is concealed during the daytime by subconsciously learned behavior of frequent voiding or decreased fluid intake. These patients tend to have severe symptoms and may need second- or third-line treatments or combination therapy.[11]

If a child has a normal, functioning bladder with adequate capacity holding an appropriate amount of urine, but does not wake when the bladder is full, he or she will have enuresis. Thus, a failure to wake in time to void is the base cause of enuresis. Anecdotally, many parents report that enuretic children are difficult to arouse; and there are good data showing that enuretic children are more difficult to arouse than their age-matched controls.[15] Some children with arousal disorders will have concurrent sleep-disordered breathing or even obstructive sleep apnea. In these children, correcting the breathing problem can improve or eliminate the enuresis.[16]

During nocturnal enuresis, voiding may take place during rapid eye movement (REM) sleep, and the child may recall a dream that involved the act of urinating.[1]

Clinical classification

Enuresis is socially inappropriate voiding: the voluntary or involuntary repeated discharge of urine into clothes or bed after a developmental age when bladder control should be established. Most children with a mental age of 5 years have obtained such bladder control.[1]
Primary nocturnal enuresis: nocturnal enuresis in which the child has never had a period of dryness longer than 6 months.
Secondary nocturnal enuresis: nocturnal enuresis recurring after a period of more than 6 months of the child being dry at night.

There are subtypes of enuresis, nocturnal-only is the most common subtype and involves incontinence only during night-time sleep, typically during the first one-third of the night. The diurnal-only subtype occurs in the absence of nocturnal enuresis and may be referred to as urinary incontinence. Those with diurnal- only subtype may have urge incontinence (i.e., have sudden urge symptoms and detrusor instability) or voiding postponement (i.e., consciously defer micturition urges until incontinence results).

Pathophysiology

Classification

Clinical classification