What is the role of EMG in the workup of bladder dysfunction?

Updated: Jan 04, 2019
  • Author: Gregory T Carter, MD, MS; Chief Editor: Elizabeth A Moberg-Wolff, MD  more...
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Electromyography (EMG) is used to diagnose the mechanistic cause of urinary retention and incontinence by measuring electrical potentials generated by depolarization of the detrusor muscle and the urethral sphincter.

Anticipated normal findings include an incremental increase in EMG activity in the external sphincter during the filling phase secondary to increased recruitment of motor units. Before voiding, diminished EMG activity in the external sphincter is expected. Relaxation of the external sphincter is followed by bladder contraction.

Abnormal EMG patterns consistent with incontinence include absence of recruitment and low levels of EMG activity, as in patients with complete SCI. An inappropriate increase in EMG activity of the sphincter may be observed in patients with urinary retention, leading to detrusor contraction against a closed sphincter or detrusor-sphincter dyssynergia. Potential findings include confirmation of detrusor-sphincter contraction dyssynergia, increased duration of bladder contractions, and uninhibited bladder contractions.

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