💧 Chapter 45: Urinary Incontinence and Polyuria

Nelson's Pediatric Symptom-Based Diagnosis | Enuresis · Daytime wetting · Diabetes Insipidus (Central vs Nephrogenic) · Diabetes Mellitus · Overactive bladder · Voiding dysfunction · Urinary tract infection · Polydipsia · Water deprivation test · Desmopressin (DDAVP)

🔍 Urinary Incontinence and Polyuria: Key Concepts

🌙 Enuresis (Bedwetting)
Primary nocturnal enuresis: never dry at night (>5y). Monosymptomatic (no daytime symptoms). Familial, delayed bladder maturation. First-line: enuresis alarm, desmopressin (DDAVP).
☀️ Daytime Incontinence
Diurnal enuresis after age 5-6y. Causes: overactive bladder (urgency, frequency), dysfunctional voiding (incomplete emptying, UTI), constipation, toileting refusal, anatomic anomalies.
⚠️ Polyuria + Polydipsia (Diabetes Insipidus)
Central DI (ADH deficiency): low urine osmolality, hypernatremia, responds to DDAVP. Nephrogenic DI (ADH resistance): normal/high ADH, no response to DDAVP, causes: lithium, pyelonephritis, genetic (AVPR2).
🩸 Diabetes Mellitus (Polyuria)
Type 1 DM: hyperglycemia, glycosuria, osmotic diuresis. Polyuria, polydipsia, weight loss, DKA. Labs: elevated glucose, ketones, A1C.
🧪 Psychogenic Polydipsia
Compulsive water drinking → dilute urine, hyponatremia (dilutional), normal ADH suppression. Differentiate from DI by water deprivation test (urine concentrates normally after dehydration).
🔬 Water Deprivation Test
Distinguish DI from psychogenic polydipsia. After dehydration: central DI → urine osmolality <300, rises with DDAVP. Nephrogenic DI → no response. Psychogenic → concentrates normally.

💡 Key takeaway: Enuresis: treat after age 6-7, first-line enuresis alarm > desmopressin. Polyuria + polydipsia: check glucose (DM), serum osmolality, urine osmolality, electrolytes. Water deprivation test differentiates central DI, nephrogenic DI, and psychogenic polydipsia.

🩺 Clinical Approach to Urinary Incontinence and Polyuria

🔹 Step 1: Distinguish incontinence (wetting) from polyuria (excessive urine output)
• Polyuria: urine output >2 L/m²/day or >4 mL/kg/hr. Associated with polydipsia.
• Incontinence: involuntary urine loss. Classify as nocturnal (enuresis) vs diurnal, monosymptomatic vs non-monosymptomatic.
🔹 Step 2: Evaluate for polyuria causes
• Diabetes mellitus: elevated glucose, ketones, A1C.
• Central DI: low urine osmolality (<300), high serum Na, responds to DDAVP.
• Nephrogenic DI: no response to DDAVP, normal/high ADH. Causes: genetic (AVPR2, AQP2), lithium, hypercalcemia, CKD.
• Psychogenic polydipsia: hyponatremia, normal ADH suppression, urine concentrates after water deprivation.
🔹 Step 3: Water deprivation test protocol
• Controlled fluid restriction, monitor weight, serum Na, urine osmolality every 1-2h.
• Stop if weight loss >5% or serum Na >150.
• Administer DDAVP (desmopressin) after dehydration phase.
• Normal: urine osmolality >800 after dehydration.
• Central DI: urine osmolality <300, rises >50% after DDAVP.
• Nephrogenic DI: urine osmolality <300, minimal rise after DDAVP.
• Psychogenic polydipsia: urine concentrates normally.
🔹 Step 4: Approach to enuresis (bedwetting)
• Primary nocturnal enuresis: never dry >6 months. Usually normal exam. First-line: enuresis alarm (best long-term cure). Second-line: desmopressin (DDAVP) orally/nasal.
• Secondary enuresis: previously dry >6 months → evaluate for UTI, diabetes, constipation, psychological stress, sleep apnea.
• Non-monosymptomatic (daytime symptoms, urgency, straining) → evaluate for bladder dysfunction, UTI, anatomic anomalies.
🔹 Step 5: Daytime incontinence (diurnal enuresis)
• Urinalysis and culture to rule out UTI.
• Bladder diary, uroflow, post-void residual.
• Overactive bladder: urgency, frequency, wetting → anticholinergics (oxybutynin).
• Dysfunctional voiding: incomplete emptying, constipation → pelvic floor therapy, timed voiding, treat constipation.
• Consider renal/bladder ultrasound for anatomic anomalies.