Diagnostic électrophysiologique de l’incontinence anale
Electrodiagnosis of anal incontinence
Neurophysiological testing is complementary to endosonography and anorectal manometry in the assessment of anal incontinence, and helps to determine the localization, the pathophysiological mechanisms and the severity of various types of lesion of the peripheral or central nervous system. Electrodiagnostic tests include: (i) electromyography (EMG) of the external anal sphincter using a disposable concentric needle; (ii) terminal motor latency (TML) measurement based on the recording of anal sphincter responses to transrectal stimulation of the anal nerve or to magnetic stimulation of the sacral roots; (iii) motor evoked potentials (MEPs) of the anal sphincter to cortical stimulation; (iv) cortical recording of the somatosensory evoked potentials (SEPs) to anal nerve stimulation; (v) quantification of sensory thresholds (QSTs) to electrical or thermal stimulation of the anorectum; (vi) cutaneoanal reflex (CAR) latency measurement to pudendal nerve or perianal stimulation; (vii) sympathetic skin responses (SSRs) of the posterior perineum. A comprehensive approach using several tests is useful in most cases. First, needle EMG is important to demonstrate muscle denervation and/or reinnervation, which must be taken into account for the interpretation of TML, MEP or CAR results. In search of peripheral neuropathy, SEPs, QSTs and SSRs are valuable to show sensory or autonomic involvement. In the absence of peripheral nerve lesion, the analyses of MEPs, SEPs, SSRs and CAR can give evidences for the presence or the absence of central nervous system lesion, at either the spinal (segmental or suprasegmental) or the supraspinal level. Thus, in patients with anal incontinence of suspected neurogenic etiology, neurophysiological tests performed by a clinical neurophysiologist experienced in the sacral nervous system, should contribute to establish the diagnosis and to guide therapeutic management.
clinical neurophysiology, electromyography, evoked potentials, external anal sphincter, quantitative sensory testing, sacral reflex, sympathetic nervous system