Lower Urinary Tract Dysfunction

Topic: Initial management of nocturia

Case 1: Hector (58 years old)

Hector, 58 years old, works at the national history museum. He complains that he needs to wake up at night several times to void. This started a year ago and he is very tired during the day. He has no significant micturition complaints during the day.
 
Medical history: Hypertension (amlodipine).
Clinical examination: DRE: normal-sized prostate, not suspicious. Malleolar oedema.
IPSS: 6 (IPSS QoL: 4).
Urinalysis: Normal.
Bladder scan: No post void residual.
Bladder diary: Frequency: day 5x, night 3x. Voided volumes: 100-480 ml. 24h diuresis: 1560 ml. Nocturnal diuresis: 36% of 24h diuresis. No urgency. No urine leakage.

What is the most likely cause of this patient’s complaint of nocturia?