Neurogenic Bladder Diagnosed Pharmacologically on the Basis of Denervation Supersensitivity

Abstract

A test described by Lapides et al. 1962 for diagnosis of neurogenic bladder, based on denervation supersenisitivity of detrusor to cholinergic stimulation, is critically reviewed. The “localized stretch response of bladder muscle” to instillation of fluid described by these authors seems to be an artifact. In a modified method developed by the author the denervation test consists of a continual reading of the intravesical pressure response to subcutaneous administration of 0.25 mg carbachol (equivalent to 2.5 mg bethanechol) after the bladder has previously been filled with 100 ml saline and allowed to accomodate. The maximum rise in pressure (cm H₂O) following the chemical stimulation, above the basal pressure prior to this, constitutes the test result. By this technique 197 tests were performed in 64 patients. It was found that normal bladders usually respond with a pressure rise of less than 15 cm H₃O; results in the range 15-20 cm H₂O are inconclusive, while greater responses indicate neurogenic bladder with increasing certainty. A normal test result does not always exclude a neurogenic defect, and the test is only semiquantitative. It depends on individual differences in sensitivity to cholinergic agents; the response is raised by emotional stress; the muscular integrity which is necessary for the response eludes exact estimation; the degree of denervation supersensitivity is known to be influenced by the level of denervation, which cannot always be localized exactly. Furthermore, the test may be influenced by the conditions for resorption at the site of injection, and by deviations of bladder volume during the examination. Nonetheless, the reproducibility of the results is acceptable. Studies of the time factor in development of denervation supersensitivity showed the test to turn positive in the course of 1-2 weeks after the lesion, sometimes later, and maximum sensitivity is not reached until months later. Restitution causes the supersensitivity to decrease, reflected in falling test results. No significance can be attached to bladder sensations experienced during the test. The denervation test is called for when it is suspected that a bladder may be of the autonomous neurogenic type, while reflex bladders are better identified by cystometry. The pronounced denervation supersensitivity calls for caution in the clinical use of cholinergic druggs in neurogenic bladders, both in therapeutical regimens, which may possibly have injurious effects, and for functional investigations, which may be highly misleading when “micturition” has been assisted by cholinergic stimulation.