What are approach considerations in the technique of acute hypoglycemia?

Updated: Aug 06, 2019
  • Author: Jasvinder Chawla, MD, MBA; Chief Editor: David C Spencer, MD  more...
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EMG studies can help quantitate sphincter dysfunction in neurologic disorders. [28] They help establish or rule out the possibility of agenesis of the striate sphincter in the preoperative assessment of the newborn with an imperforate anus. Electrical studies not only localize the sphincter precisely, if it is present, but also determine its functional capacity. The anal sphincter may sustain traumatic injury in several conditions, including during parturition, prostatectomy, or rectal surgery for repair of an anal fistula or prolapse. EMG helps determine the extent of damage in such cases and aids in establishing the differential diagnoses for fecal incontinence. [29]

The anal and external urethral sphincters share a common segmental derivation. Thus, confirming the integrity of the anal sphincter provides an important, albeit indirect, guide in ilioconduit surgery for prominent urologic dysfunction. EMG of the urethral sphincter ideally involves the help of urologists working in a laboratory equipped with tools for urodynamic investigations.

Abnormality of the striated sphincter may occur from a lesion of the peripheral nervous system (PNS), central nervous system (CNS), or a combination of both. Weakness from central lesions causes reduction in voluntary discharges with preservation of reflexive activation. The interference pattern is incomplete, with motor unit potentials of normal amplitude but discharging at a low frequency. With complete loss of voluntary activity, the low frequency discharge normally seen at rest continues during maximal effort contraction. Lesions involving the PNS are generally localized to the cauda equina or the sacral or pudendal plexus.

Needle examination of the subcutaneous external anal sphincter (EAS) muscles alone likely suffices in most patients with conus medullaris or cauda equina disorders and those with symptoms related to central nervous system disorders. [2, 22] However, examination of the deeper muscles is necessary when evaluating for sphincteric dysfunction. [2] The deeper muscles are typically found with a needle insertion perpendicular to the mucosal surface slanted at about 30° to the anal canal axis, usually at a depth of 15-25 mm. [2]

In an incomplete paralysis, a volitional effort recruits a few motor units that fire at a high frequency. In contrast to central paralysis, the surviving units show a polyphasic waveform and a long duration. In an acute cauda equina syndrome, the initial paralysis may result from a functional block. Axonal degeneration, if present, gives rise to fibrillation potentials, positive sharp waves, and complex repetitive discharges.

Patients often have a mixture of central and peripheral paresis in congential malformation, vascular disease, or traumatic injury of the conus medullaris. Spina bifida with meningomyelocele characteristically affects both upper and lower motor neurons. [30] EMG of the anal sphincter in these cases reveals absent or markedly reduced voluntary activity. Reflexive contraction, if present, shows isolated high-frequency discharges of a few motor units. Complete damage to the sacral segment of the conus medullaris precludes sphincter response either voluntarily or reflexively. Spontaneous potentials recorded in these cases indicate the involvement of the anterior horn cells. [30]

Amyotrophic lateral sclerosis (ALS) typically spares the sphincter, even when the limb muscles show evidence of conspicuous denervation. [31] In contrast, abnormal spontaneous activity serves as a specific marker for neuronal degeneration of Onuf’s nucleus in multiple system atrophy [32] and progressive supranuclear palsy. [33] In one series of 126 patients in whom multiple system atrophy was suspected, 82% of those with definite diagnosis had abnormal sphincter study findings. Abnormal findings also help differentiate multiple system atrophy from Parkinson disease. [28]

In recent studies, [34, 35] utilization of urethral sphincter electromyography (US-EMG) as a supplement to the external anal sphincter EMG (EAS-EMG) was proposed for routine electrophysiological method in patients with a suspicion of MSA. The differences of multiple parameters of EAS-EMG were more significant than those of US-EMG for MSA cases.

Reports on autonomic systems like lower urinary tract and bowel functions in patients with critical illness polyneuropathy (CIP) are not available in medical literature. Reitz, [36] in a recent study, has revealed that sensory and motor pathways controlling the lower urinary tract, including detrusor overactivity and detrusor overactivity incontinence, might be affected by CIP.

In a study by Podnar, [37] it has been shown that the current study complements previous reports in men, supporting the high clinical utility of sacral neurophysiologic studies in confirmation and exclusion of sacral neuropathic lesions.

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