What causes nocturnal enuresis in children?

What Causes Bedwetting in Children

Bedwetting in children is primarily caused by a hereditary delay in maturation of three key mechanisms: nocturnal polyuria (excessive nighttime urine production), detrusor overactivity (uninhibited bladder contractions), and increased arousal threshold (difficulty waking to bladder signals). 1

Genetic Factors

Strong hereditary predisposition is the dominant cause of primary nocturnal enuresis. The genetic influence is striking and should be the first consideration:

• Children have a 44% risk when one parent was enuretic and 77% risk when both parents were affected, compared to only 15% in children from non-enuretic families 2, 1
• Approximately one-third of fathers and one-fifth of mothers of enuretic children were themselves bedwetters 2
• Genetic linkage studies have identified specific loci on chromosomes 12 (ENUR 2) and 13 (ENUR 1), though the exact pathophysiology remains unclear 2

Developmental and Physiological Mechanisms

The normal acquisition of urinary continence occurs in three sequential steps, and disruption of any step can cause enuresis 2:

Bladder Capacity and Function

• Reduced functional bladder capacity was identified in early studies, though more recent cystometric studies show normal nocturnal bladder capacity in many enuretic children 2
• Uninhibited bladder contractions (similar to infantile voiding patterns) are identified more commonly in enuretic children, though their relationship to actual bedwetting episodes remains unclear 2

Nocturnal Polyuria

• Children with nocturnal enuresis produce urine at higher rates during the night 3
• This represents a delay in the normal maturation of nocturnal urine concentration mechanisms 4

Arousal Dysfunction

• Enuretic children require louder tones to awaken from sleep compared to non-enuretic children, supporting parental observations that these children are "very difficult to awaken" 2
• A dysfunctional arousal system during sleep may be a key etiologic factor for a subgroup of children 2
• Bedwetting occurs randomly across all sleep stages in proportion to time spent in each stage 2

Sleep-Related Causes

Upper airway obstruction with sleep apnea is an important and treatable cause:

• Heavy snoring and nocturnal sleep apnea can cause bedwetting 2
• Some children become dry after upper airway obstruction is surgically relieved 1
• Screen for habitual snoring, witnessed apneas or gasping, restless sleep, unusual sleeping positions, and daytime sleepiness or behavioral problems 1

Bowel Dysfunction

Constipation is a critical comorbid condition that must be identified and treated:

• Bladder and bowel function are closely interrelated 2
• If concomitant constipation is not treated first, it may be difficult to get the child dry 2
• Constipation is probable if bowel movements occur every second day or less, or if stool consistency is usually hard 2
• Fecal incontinence is common in constipated children and should be specifically asked about 2

Medical Conditions to Exclude

While uncommon, certain medical conditions must be ruled out 2:

• Diabetes mellitus or kidney disease (screen with questions about recent tiredness, weight loss, and polyuria)
• Urinary tract infections (more common in secondary enuresis) 5
• The sole obligatory laboratory test is a urine dipstick 2

Psychological and Stress Factors

Psychological factors are contributory in only a minority of children, primarily those with secondary enuresis:

• Secondary enuresis (resumption after ≥6 months of dryness) may follow stressors such as parental divorce, school trauma, sexual abuse, or hospitalization 2
• Somatic and psychological comorbid conditions are more common in children who were previously dry than in those with primary enuresis 2
• Children with attention deficit hyperactivity disorder may need psychiatric treatment in parallel with anti-enuretic therapy 2

Important Clinical Distinctions

Distinguish monosymptomatic from non-monosymptomatic enuresis to guide evaluation:

• Children with only urgency, decreased/increased voiding frequency, or moderate intermittent daytime incontinence differ from those with alarming symptoms 2
• Children who void with a weak stream, must use abdominal pressure, or have continuous incontinence must be sent to a specialized center without delay 2

Common Pitfalls

• Do not assume bedwetting is purely psychological – it is primarily a hereditary delay in somatic maturation 4
• Do not overlook constipation – it must be treated before enuresis therapy can succeed 2
• Do not miss sleep apnea – ask specifically about snoring and sleep disturbances 1
• Always obtain a family history – the absence of parental enuresis makes primary functional nocturnal enuresis unusual 2