Selective nocturnal polychyuria

Specialty: Nephrology and urology.

• selective nocturnal urination frequency
• frequent urination only at night

Why it occurs

• Peripheral venous insufficiency with malleolar edema (during night recumbency, the interstitial fluid accumulated in the lower extremities during the day is reabsorbed, sharply increasing the intravascular volume and activating repeated diuresis)
• Obstructive sleep apnea (intermittent nocturnal hypoxia raises intrathoracic pressure stimulating the release of atrial natriuretic peptide, resulting in polyuria and frequent urination only during the night)
• Mild congestive heart failure (fluid redistribution while lying down temporarily optimizes renal perfusion causing an increase in nocturnal diuresis)
• Alterations in the circadian rhythm of solute excretion (due to aging or autonomic neuropathy where the nocturnal peak of ADH secretion is lost)

Initial workup

24-hour voiding diary detailing daytime and nighttime volumes separately to confirm nocturnal polyuria (>33% of total daily urine output emitted at night); venous Doppler ultrasound of the lower limbs; full nocturnal polysomnography to confirm obstructive sleep apnea; Transthoracic echocardiogram to evaluate left ventricular ejection fraction and filling pressures.

Standard management

• Furosemide — 10-20 mg orally administered in the middle of the afternoon, approximately at 4:00 p.m. or 5:00 p.m., to force diuresis of accumulated edema before the patient goes to bed, thus reducing nocturnal urination
• Desmopressin — 0.1 mg orally before bedtime, selectively indicated for idiopathic nocturnal polyuria in the elderly after rigorously ruling out basal hyponatremia; monitor serum sodium 3 and 7 days after starting treatment
• Optimization of cardiological treatment with ACEIs or beta-blockers.