Long Exercise Test in Periodic Paralysis: A Bayesian Analysis

Simmons, Daniel; Lanning, Julie; Cleland, James; Puwanant, Araya; Twydell, Paul; Griggs, Robert C.; Tawil, Rabi; Logigian, Eric L.

doi:10.1002/mus.26157

Cited by 12 publications

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References 15 publications

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“…The study by Simmons et al 9 in this issue of Muscle & Nerve elegantly summarizes the methodological issues and discrepancies that have been observed in previous reports of the LET in the primary periodic paralyses. They offer a logical, coherent set of LET cutoff guidelines that are based on their analysis of a cohort of 55 patients with genetically or clinically confirmed periodic paralysis and 125 control patients (healthy volunteers and patients with other neuromuscular disorders) by using a Bayesian analysis.…”

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confidence: 93%

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confidence: 99%

“…In an extensive analysis of their data, Simmons et al 9 determined the optimal cutoff values for the LET that, when positive, achieve a 95% posttest probability of periodic paralysis for patients with various pretest probabilities of having periodic paralyses. They also found that using the peak-to-nadir decrement was preferable to the baseline-to-nadir decrement method to assess for periodic paralysis, and there was no significant difference when using amplitude versus area decrements.…”

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confidence: 99%

“…Likewise, when setting cutoff values to obtain very high specificities, the sensitivity of a test diminishes, meaning that not all patients with the disorder will have an abnormal test result. Simmons et al 9 have refined the LET into an essential and useful tool in the diagnosis of primary periodic paralyses. Their analysis of this very large cohort of genetically confirmed and/or clinically definite periodic paralysis patients now should set the standard when using the LET.…”

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Looking for periodic paralysis: Optimizing the long exercise test

Shapiro

Preston

2018

Muscle and Nerve

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The primary periodic paralyses are a group of very rare, genetic ion channel disorders characterized by transient attacks of severe flaccid weakness accompanied by serum potassium levels that are high, low, or normal. 1,2 In patients who present with characteristic episodes of flaccid weakness with abnormal potassium levels, especially when a family history is present, or in patients in whom genetic testing for one of the periodic paralyses confirms a pathogenic mutation, the clinical diagnosis is made rather easily. However, in those patients for whom this is not the case, the long exercise test (LET) is an electrodiagnostic technique that can be used to help establish the diagnosis. The LET is performed in the electromyography laboratory and entails measuring the baseline compound muscle action potential (CMAP) area or amplitude at rest and then measuring the CMAP amplitude or area over a period of 40-60 min after 5 min of isometric exercise of the recorded muscle, looking for an increment followed by a prolonged gradual decline. This methodology takes advantage of the fact that, in the periodic paralyses, attacks of weakness are known to be provoked by periods of rest after vigorous exercise. Although much has been written about the LET in the periodic paralyses, there are no firmly agreed upon cutoff values for amplitude and area decrements to define an abnormal LET result, and methods used to document these decrements vary. [3][4][5][6][7][8] In addition, cutoff values have classically been determined by studying a normal population, determining the mean and SD and setting the cutoff values at 2 SD above the mean.The study by Simmons et al. 9 in this issue of Muscle & Nerve elegantly summarizes the methodological issues and discrepancies that have been observed in previous reports of the LET in the primary periodic paralyses. They offer a logical, coherent set of LET cutoff guidelines that are based on their analysis of a cohort of 55 patients with genetically or clinically confirmed periodic paralysis and 125 control patients (healthy volunteers and patients with other neuromuscular disorders) by using a Bayesian analysis. Bayesian analysis, named for the English mathematician Thomas Bayes, is a statistical procedure that takes into account known information about a particular sample population variable that is being studied to guide and interpret the statistical analysis. 10 Simply put, the fundamental question when performing a diagnostic test is: how much does an abnormal test influence the likelihood that the patient truly has the disorder? If a clinician assesses the probability that an individual has the disorder as low (e.g., 25%) and a positive test result increases the probability to 35%, the test is of little use (despite being positive). However, if a positive test increases the probability to 95%, the diagnosis is almost certain. Bayesian analysis has been used previously to optimize the diagnosis of various entrapment neuropathies. 11 Bu using Bayesian analysis, the pretest probability distrib...

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Looking for periodic paralysis: Optimizing the long exercise test

Shapiro

Preston

2018

Muscle and Nerve

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“…A progressive and slow decline in CMAP amplitude and area is characteristic feature of periodic paralysis. 4 There are only sparse case reports of TPP from the Middle East region and none of them have described the detailed electrophysiological findings. 5 Here we describe a patient who was diagnosed to have TPP and his electromyography showed characteristic decrement during prolonged exercise test.…”

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Decremental Response on Prolonged Exercise Test in a Patient With Thyrotoxic Periodic Paralysis

Ostwal

Alshaheen

2022

MNJ

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Paralysis of acute onset often presents a diagnostic challenge for the assessing physician because of a large number of differential diagnosis and overlap of clinical features among them. Thyrotoxic periodic paralysis is an uncommon cause of acute weakness. In addition to serological tests, electromyography findings during prolonged exercise test are very helpful in confirming the diagnosis. Only a few case reports of thyrotoxic periodic paralysis have been published from Middle East and none of them have described this specific electrophysiological data. A man in his 20s presented to us with acute onset weakness in both legs which was evaluated further and found to have hypokalemia. The work up for the etiology revealed thyrotoxic status and a final diagnosis of thyrotoxic periodic paralysis was established. The prolonged exercise test performed in this patient showed typical progressive decremental respsonse with nadir at 40 minutes after the exercise.

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The long exercise test as a functional marker of periodic paralysis

et al. 2021

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Aims:The aim of this study was to evaluate the sensitivity of the long exercise test (LET) in the diagnosis of periodic paralysis (PP) and assess correlations with clinical phenotypes and genotypes.Methods: From an unselected cohort of 335 patients who had an LET we analyzed 67 patients with genetic confirmation of PP and/or a positive LET.Results: 32/45 patients with genetically confirmed PP had a significant decrement after exercise (sensitivity of 71%). Performing the short exercise test before the LET in the same hand confounded results in four patients. Sensitivity was highest in patients with frequent (daily or weekly) attacks (8/8, 100%), intermediate with up to monthly attacks (15/21, 71%) and lowest in those with rare attacks (9/16, 56%) (p = .035, Mann-Whitney U-test). Patients with a positive LET without confirmed PP mutation comprised those with typical PP phenotype and a group with atypical features.Discussion: In our cohort, the LET is strongly correlated with the frequency of paralytic attacks suggesting a role as a functional marker. A negative test in the context of frequent attacks makes a diagnosis of PP unlikely but it does not rule out the condition in less severely affected patients.

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Long Exercise Test in Periodic Paralysis: A Bayesian Analysis

Abstract: For confirmation of PP, our data endorse the diagnostic utility of peak-to-nadir LET methodology using 40% amplitude or 50% area decrement cutoffs for PreTP ≤50%. Muscle Nerve, 2018.

Cited by 12 publications

References 15 publications

Looking for periodic paralysis: Optimizing the long exercise test

Looking for periodic paralysis: Optimizing the long exercise test

Decremental Response on Prolonged Exercise Test in a Patient With Thyrotoxic Periodic Paralysis

The long exercise test as a functional marker of periodic paralysis

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