The value of external anal sphincter electromyography for the diagnosis of multiple system atrophy

Mov Disord. 2000 Nov;15(6):1148-57. doi: 10.1002/1531-8257(200011)15:6<1148::aid-mds1014>;2-6.


Objective: To assess the value of external anal sphincter electromyography (ASEMG) for the diagnosis of multiple system atrophy (MSA) among various causes of parkinsonism. ASEMG denervation profiles have previously been proposed as a diagnosis test for MSA, but their specificity is disputed.

Methods: ASEMG variables of 52 parkinsonian patients were analyzed according to the clinical diagnosis: MSA (n = 31) or no MSA (n = 21). Mean motor unit potential duration, percentage of polyphasicity, and the electromyographer's interpretation were analyzed according to clinical diagnosis, disease duration, genitourinary symptoms, gender, parity, and history of pelvic surgery.

Results: All patients with MSA showed ASEMG denervation. Mean motor unit potential duration was the most discriminant variable. No patient with MSA had a mean duration less than 12 ms and no patient without MSA had one greater than 16 ms. ASEMG discriminates between patients with MSA and Parkinson's disease. Using a threshold of 13 ms, the sensitivity was 80% and specificity was almost 70% (positive predictive value, 80%) for the diagnosis of MSA. Age, history of pelvic surgery, and to a lesser extent, female gender, parity, disease duration, and presence of urinary symptoms increased the likelihood of abnormal ASEMG.

Conclusion: ASEMG was highly sensitive and rather specific for the diagnosis of MSA.

Publication types

  • Evaluation Study
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adult
  • Aged
  • Anal Canal / physiopathology*
  • Diagnosis, Differential
  • Electromyography*
  • Female
  • Humans
  • Male
  • Middle Aged
  • Multiple System Atrophy / complications
  • Multiple System Atrophy / diagnosis*
  • Multiple System Atrophy / physiopathology
  • Parkinson Disease, Secondary / etiology*
  • Parkinson Disease, Secondary / physiopathology
  • Predictive Value of Tests
  • Retrospective Studies
  • Sensitivity and Specificity