Urodynamic distinctions between idiopathic detrusor overactivity and detrusor overactivity secondary to multiple sclerosis

Objectives: To evaluate the urodynamic characteristics of neurogenic detrusor overactivity (NDO) secondary to multiple sclerosis (MS) compared with idiopathic DO (IDO) to determine whether urodynamic distinctions could differentiate the different etiologies of DO. Methods: The urodynamic characteristics of DO in women with MS (n = 54) were compared with the overactive contractions found in women with lower urinary tract symptoms and IDO (n = 42). Among other parameters, the amplitude of the first overactive contraction, maximal detrusor contraction, and threshold volume for the first overactive contraction were evaluated to assess the DO severity. A sensitivity analysis using cutoff values determined from those urodynamic parameters that differed between the patient groups is presented. Results: The amplitude of the first overactive contraction was statistically greater in the patients with MS and NDO compared with patients with IDO (28.3 cm H₂O versus 20.5 cm H₂O, P = 0.003), as was the maximal detrusor contraction (46.4 cm H₂O versus 30.8 cm H₂O, P = 0.002). The threshold volume for DO was greater among patients with NDO (186.8 mL versus 150.5 mL, P = 0.037), likely secondary to the elevated postvoid residual urine volume noted among patients with MS (P = 0.049). Using a cutoff value of 30 cm H₂O for amplitude of the first overactive contraction achieved a positive predictive value of 88% for identifying MS in our data set. Conclusions: The urodynamic characteristics of NDO differed significantly from those of IDO. Additional investigation is required to determine whether these differences are due to neurogenic influences directly on the detrusor muscle through aberrant innervation or by other mechanisms, such as enhanced outlet resistance during voiding.