Implications of underactive bladder syndrome for nocturia: Do we need urodynamic assessment?

Nocturia is a common urological symptom defined by the International Continence Society (ICS) as “the number of times urine is passed during the main sleep period. Having woken to pass urine for the first time, each urination must be followed by sleep or the intention to sleep. This should be quantified using a bladder diary” [ [1] ]. The prevalence of nocturia is high in both genders and increases with age. Nocturia or nocturnal polyuria can be caused by wide-ranging nonurological factors, such as cardiovascular disease, obstructive sleep apnoea, polypharmacy, or learnt behaviour. These mainly contribute to an increase in the rate of urine production. Alongside these, factors impairing the reservoir function of the bladder need to be considered. Underactive bladder (UAB) is characterized by a slow urinary stream, hesitancy, and straining to void, with or without a feeling of incomplete bladder emptying, sometimes with storage symptoms [ [2] ]. UAB has a varied phenotype, and for many patients with UAB the storage symptoms can be prominent and problematic. Urgency and increased daytime frequency are present in a large proportion of patients, meaning that overactive bladder syndrome (OAB) commonly coexists with UAB.