Value of sphincter electromyography in the diagnosis of multiple system atrophy

Abstract

It is clinically important, to distinguish between idiopathic Parkinson's disease (IPD) and multiple system atrophy (MSA) not only because of the implications for prognosis but also because urinary incontinence is often an early troublesome feature of MSA and by making the correct neurological diagnosis inappropriate urological surgery may be avoided. Onuf's nucleus in the sacral cord is the location of the anterior horn cells innervating the sphincters, and it is among central nervous system sites affected by neuronal cell loss in MSA but not in IPD. A systematic analysis of motor units recorded from the sphincter looking for changes of chronic reinnervation has therefore been used to distinguish between these conditions. Sphincter electromyography (EMG) was carried out in 126 patients with suspected MSA with review of their case notes up to 2 years later. Of those in whom a diagnosis of MSA was made, 82% had had an abnormal sphincter EMG.

Sphincter EMG for Diagnosing Multiple System Atrophy and Related Disorders

“…However, some of these reports were published before a definition of MSA was established. Recent studies have reported almost normal EAS-EMG in patients with typical IPD 38,47,53,67 . Stocchi's study (1997) is important, since EMG in patients with IPD and MSA was performed by researchers blinded to the diagnosis.…”

“…Palace et al proposed that either of two criteria is sufficient to diagnose neurogenic changes in the EAS-EMG: (a) more than 20% of MUPs have a duration > 10 msec, or (b) the average duration of MUPs > 10 msec, particularly including the late components. 38 When satellite potentials were excluded, the duration of MUPs did not differ significantly between Parkinson's disease and MSA. 48 When lower motor neuron-type abnormalities are not apparent, it is reported that abnormal MUP recruitment pattern suggests pyramidal tract involvement.…”

“…33,37 The first reports on neurogenic changes of EAS-EMG in MSA are attributed to Sakuta et al (1978). 62 Since then, EAS-EMG results for over 500 MSA patients have been reported, with abnormality rates of more than 70% in many studies 5,30,36,38,47,53,62,64,71 . EAS-EMG is better tolerated and yields identical results to those from EUS investigation 5 .…”

“…Two of these 4 patients exhibited neurogenic changes in MUPs. 50 Abnormal sphincter EMG was also reported in 5 of 12 patients by Valldeoriola et al (1995) 71 , and in 2 of 8 patients by Palace et al (1997) 38 . Libelius and Johansson (2000) also described anal sphincter EMG abnormalities in 2 of 3 patients with PSP.…”

Multiple system atrophy presenting as central sleep apnoea: Fig. 1.—

“…An external anal sphincter electromyogram [1] was performed. This was abnormal, demonstrating a severely depleted interference pattern and changes of chronic re-innervation.…”