Monosymptomatic nocturnal enuresis

Specialty: Pediatrics.

• Isolated primary nocturnal enuresis
• involuntary urination during sleep
• nighttime urinary incontinence

Why it occurs

• Maturational delay in bladder control and the awakening mechanism (high awakening threshold due to bladder fullness)
• Excessive nocturnal urine production (relative deficit in circadian secretion of antidiuretic hormone or vasopressin)
• Reduced functional bladder capacity at night (detrusor overactivity exclusive to sleep)
• Genetic factors and family history (high heritability if both parents suffered from enuresis)
• Sleep disorders or obstructive sleep apnea (tonsillar hypertrophy that alters the secretion of atrial natriuretic peptide due to increased intrathoracic pressure)

Initial workup

Preparation of a voiding and fluid intake diary for a minimum of 7 consecutive days. Urinalysis in the first urination in the morning (systematic and sediment, urinary density to assess ability to concentrate, and test strip to rule out glycosuria and proteinuria). Urine culture if there is suspicion of infection. Renal and bladder ultrasound with assessment of post-void voiding residue (indicated if there are daytime symptoms or refractoriness). Lumbosacral spine x-ray or spinal ultrasound/MRI only in suspected spinal dysraphism.

Standard management

• Desmopressin — synthetic analogue of vasopressin that reduces nocturnal urine production; dosage of 120 to 240 mcg sublingually or 0.2 to 0.4 mg orally at bedtime; requires strict fluid restriction one hour before and 8 hours after intake to avoid dilutional hyponatremia
• Oxybutynin — anticholinergic indicated only in non-monosymptomatic enuresis with detrusor overactivity; dose of 2.5 to 5 mg orally at night
• Imipramine (tricyclic antidepressant with anticholinergic and noradrenergic effects, relegated to third line due to its narrow therapeutic margin and risk of cardiotoxicity in overdose; doses of 10 to 25 mg before bedtime under close monitoring).