To study the effects of subcutaneous bethanechol on the afferent nervous system and correlate these with the efficiency of this treatment in women with impaired detrusor contractility and to evaluate whether patients likely to respond to bethanechol can be identified before treatment through sensation evaluation.

Eighteen women with impaired detrusor contractility were given subcutaneous bethanechol for 10 days, and the flow pattern and postvoid residual urine volume were monitored. The afferent nervous system was studied before and after therapy by evaluating the sensation of filling during cystometry and by determining the bladder electrical perception threshold (EPT).

At the end of therapy, 61% voided without a postvoid residual volume. In these women, the sensation of filling and electrical sensitivity were significantly increased compared with before treatment. In women who still voided with a postvoid residual volume, the sensation of filling had increased to a lesser extent and no change in EPT was found. Women in whom bethanechol was unsuccessful had a higher pretreatment EPT than women who were successful. No such difference was found for the sensation of filling.

An increase in bladder sensitivity correlated with improvement in bladder emptying and can be evaluated by studying the sensation of filling and EPT. Patients likely to respond to bethanechol can be identified before treatment on the basis of the EPT level. Therefore, it would be valuable to initiate EPT measurement in the diagnosis of patients with impaired detrusor contractility.