Abstract
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. 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. 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. 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.
Highlights
As we previously observed a significant decrement occurring after short exercise test (SET) (3 Â 10 s bouts of exercise separated by 1 min), we considered the long exercise test (LET) positive if there was >40% decrement between peak SET amplitude and the post-LET exercise Compound muscle action potentials (CMAP)
Our study demonstrates that the sensitivity of the LET is strongly correlated with disease activity
All patients with frequent attacks had a positive LET compared to just over half of those with rare attacks or progressive weakness. This confirms that patients who have more frequent spontaneous attacks of weakness are more likely to have an attack following a standardized provocation maneuver. It is useful in clinical practice as it indicates patients with frequent attacks but negative LET are unlikely to have periodic paralyses (PP), whereas those with rare attacks and negative LET should be considered for genetic testing if clinical suspicion is strong
Summary
The primary periodic paralyses (PP) are characterized by episodic muscle weakness and include hypokalemic PP (hypoPP), hyperkalemic PP (hyperPP) and Andersen-Tawil syndrome (ATS) due to mutations in voltage gated ion channels. The diagnosis is based on clinical. The primary periodic paralyses (PP) are characterized by episodic muscle weakness and include hypokalemic PP (hypoPP), hyperkalemic PP (hyperPP) and Andersen-Tawil syndrome (ATS) due to mutations in voltage gated ion channels.. Presentation supported by genetic and electrophysiological findings but can be challenging when clinical and laboratory information do not agree.. Genetic testing has been the gold standard for diagnosis, but a pathogenic mutation is found in only 60% to 70% of patients meeting clinical criteria for PP.. The literature suggests that the long exercise test (LET) is highly sensitive and specific.. The aim of this study was to assess sensitivity in our cohort and correlate electrophysiology with phenotype and genotype. Sensitivity was calculated using genetic testing as the gold standard. The level of statistical significance was set at p < .05
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