Leak point of incontinence: a measure of the interaction between outlet resistance and bladder capacity.

A total of 48 consecutive spina bifida patients undergoing routine urodynamic studies was classified into 2 groups depending upon whether they demonstrated uninhibited bladder contractions. Of the patients 34 demonstrated detrusor hyperreflexia and 14 had detrusor areflexia. These 2 groups were then subdivided depending on the continence status. Of the areflexic and hyperreflexic groups, 6 and 7 patients, respectively, were wet despite at least 2 years of conservative medical management. Leak point pressure and leak point volume were determined in all patients and results were compared in both subgroups. In the hyperreflexic groups leak point volume but not leak point pressure was significantly different between the wet and dry patients. The areflexic group demonstrated the opposite finding, that is the leak point pressure but not the leak point volume was significantly different between wet and dry patients. From these studies we determined that in the areflexic group leak point pressure was useful to predict incontinence, whereas in the hyperreflexic group leak point volume was more useful. The addition of the measurement of leak point pressure and leak point volume during routine urodynamic studies in myelodysplastic patients enhances accurate diagnosis and may select those who will best benefit from bladder augmentation and/or a procedure to increase outlet resistance.