Detrusor function with lesions of the conus medullaris.

Conventional urodynamic evaluation is unable to distinguish between a pure conus lesion and one with concomitant cauda equina involvement. Lumbosacral evoked potentials to tibial nerve stimulation assesses the sensory root and dorsal horn interneurons of the L5 to S2 spinal cord segments. This allows for the diagnosis of a pure lesion of the conus medullaris with preservation of the sensory root response (R wave) with absence of the dorsal horn gray matter response (S wave). Urodynamic evaluation in 5 patients with a conus lesion showed a variety of detrusor responses ranging from hyperreflexia through areflexia with decreased compliance to areflexia with normal compliance. The ability to diagnose a pure conus lesion may have prognostic significance as newer modalities of treatment emerge, all of which require intact gray matter of the spinal cord.