Objective To evaluate the diurnal and nocturnal bladder reservoir function in patients with refractory primary nocturnal enuresis (PNE). Patients and methods Ninety-five children (68 boys, 27 girls, mean age 9.3 years) with significant PNE (o3 wet nights/week) that was refractory to treatment with desmopressin t an enuretic alarm were assessed using detailed recording of voiding frequency and urinary volume both day and night, natural filling cystometry during the day and continuous cystometry with simultaneous electroencephalogram monitoring during sleep at night. Results Patients could be broadly categorized into two groups. Group A comprised those with normal daytime urodynamics and functional bladder capacity (FBC) on detailed frequency-volume recording, but who developed marked detrusor instability associated with a significant reduction in nocturnal FBC and small-volume voiding only after sleep at night (33 patients, 35%); and group B, those with abnormal daytime urodynamics and with reduced FBC and small-volume voiding both day and night, but who somehow managed to mask their bladder symptoms during the day (62 patients, 65%). There was no evidence of nocturnal polyuria in either group and the ratios of day : night urinary output volumes for type A and type B patients were 1.48 and 1.99, respectively. Conclusions A reduction in nocturnal FBC, either occurring only after sleep at night in association with the appearance of detrusor instability in patients with normal daytime urodynamics and FBC, or as a manifestation of occult voiding dysfunction or bladder outlet obstruction that affects the bladder reservoir function both day and night, appears to be a common factor and probably the main cause for a mismatch between nocturnal urine output and bladder storage capacity in patients with severe bed-wetting that was refractory to treatment.

Abnormal bladder function, including small functional capacity, instability during sleep and marked detrusor hypercontractility, was common in our enuretic children in whom treatment failed. More importantly, nocturnal enuresis may be the only presenting symptom and there may be a response to desmopressin with a decreased number of wet nights even in cases of significant underlying bladder dysfunction. These findings may have important implications for our management strategy for monosymptomatic primary nocturnal enuresis.

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