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When is Onuf’s nucleus involved in multiple system atrophy? A sphincter electromyography study
  1. T Yamamoto1,
  2. R Sakakibara1,
  3. T Uchiyama1,
  4. Z Liu1,
  5. T Ito1,
  6. Y Awa2,
  7. K Yamamoto2,
  8. M Kinou2,
  9. T Yamanishi3,
  10. T Hattori1
  1. 1Department of Neurology, Chiba University, Chiba, Japan
  2. 2Department of Urology, Chiba University
  3. 3Department of Urology, Dokkyo Medical College, Tochigi, Japan
  1. Correspondence to:
 Dr Ryuji Sakakibara
 Neurology Department, Chiba University, 1-8-1 Inohana Chuo-ku, Chiba 260-8670, Japan;


Background: External anal sphincter (EAS) electromyography (EMG) abnormalities can distinguish multiple system atrophy (MSA) from Parkinson’s disease in the first five years after disease onset. However, the prevalence of the abnormalities in the early stages of MSA is unknown.

Objectives: To present EAS-EMG data in the various stages of MSA.

Methods: 84 patients with “probable” MSA were recruited (42 men, 42 women; mean age 62 years (range 47 to 78); mean disease duration 3.2 years (0.5 to 8.0; <1 year in 25%); 50 cerebellar form (MSA-C), 34 parkinsonian form (MSA-P)). EAS motor unit potential (MUP) analysis and EMG cystometry were carried out in all patients.

Results: The overall prevalence of neurogenic change of the EAS MUP was 62%—52% in the first year after disease onset, increasing to 83% by the fifth year (p<0.05); it also increased with severity of gait disturbance (p<0.05), storage and voiding disorders, and detrusor sphincter dyssynergy (NS). The neurogenic change was not correlated with sex, age, MSA-P/C, postural hypotension, constipation, erectile dysfunction in men, underactive or acontractile detrusor, or detrusor overactivity. In 17 incontinent patients without detrusor overactivity or low compliance, urinary incontinence was more severe in those with neurogenic change than in those without (p<0.05).

Conclusions: Involvement of Onuf’s nucleus in MSA is time dependent. Before the fifth year of illness, the prevalence of neurogenic change does not seem to be high, so a negative result cannot exclude the diagnosis of MSA.

  • EAS, external anal sphincter
  • MSA, multiple system atrophy
  • MSA-C, cerebellar form of multiple system atrophy
  • MSA-P, parkinsonian form of multiple system atrophy
  • MUP, motor unit potential
  • PVR, post-void residual
  • Onuf’s nucleus
  • multiple system atrophy
  • external sphincter electromyography
  • lower urinary tract dysfunction
  • autonomic nervous system

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  • Competing interests: none declared

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