Does the absence of anal reflexes guarantee a "safe bladder" in children with spina bifida?

Increased detrusor pressure is a risk factor for renal damage in patients with neuropathic bladder, and probably requires inappropriate contraction of the external urethral sphincter. It seems logical that the absence of sacrally-mediated anal reflexes in a child with spina bifida makes such sphincteric spasm unlikely. One report has suggested that, in such circumstances, neuropathic bladder behaviour is usually predictable and safe. This article examines the reliability of this assumption, and whether routine urodynamic studies can be, therefore, safely omitted in this group.

76 children and adolescents (aged 3 - 18 years) with spina bifida were tested for the presence of the anocutaneous reflex immediately prior to video-urodynamic studies, on entry into a therapeutic trial. The relationship between the anal reflex status and two surrogate indicators of urethral sphincter function, namely maximal detrusor pressure (MDP) and leak point pressure (LPP), was analysed.

Only 11 (14 %) children had a positive reflex. Their mean MDP and their mean LPP were not statistically significantly greater than those in children without an intact reflex. Indeed the reflex was absent in the only two patients with MDP, > or = 100 cm H2O, and in the only five children with LPP, > or = 60 cm H2O.

The absence of anal reflexes is a poor predictor of safe bladder pressures in children with spina bifida. There is no justification for depriving such a population of routine urodynamic assessment on this basis. Our impression remains that there is probably no such entity as a predictably safe neuropathic bladder.