The Importance of the Bulbocavernosus Reflex

The BCR consists of the contraction of the bulbocavernosus muscle in response to squeezing the glans penis or clitoris, and is mediated through the pudendal nerve. In case of a complete lesion, the presence of BCR is indicative of intact S2-S4 spinal reflex arcs and loss of supraspinal inhibition, determining an upper motor neuron (UMN) lesion, its absence a lower motor neuron (LMN) lesion. The BCR further helps distinguish conus medullaris from cauda equina syndromes. Sensory or motor function in the most caudal sacral segments, not BCR, defines the sacral sparing as part of the International Standards for Neurological Classification of Spinal Cord Injury (ISNCSCI). Sphincter dysfunctions are addressed in the International Standards for the Assessment of Autonomic Function after SCI (ISAFSCI). However, the ISAFSCI does not include the BCR, and is not part of the ISNCSCI. Yet, determination of the type of lesion, UMN or LMN, is very useful for the clinicians, and has important prognostic and therapeutic implications for bowel, bladder, and sexual function: UMN lesions are associated with detrusor and rectum hyperactivity, reflex erection and ejaculation, while the opposite is seen in patients with LMN lesions. BCR is complementary to the voluntary contraction of the external anal sphincter and should be added to ISNCSCI and ISAFSCI classifications, which should ultimately benefit patient care and research activities.