Table 4.

The Different Categories of Periodic Paralyses (PP) with Membrane Excitability Disorder and Associated Findings

HypoPP NormoPPHyperPPTPP 1 ATS
Main clinical features Weakness episodes lasting hrs to days w/concomitant hypokalemiaWeakness episodes lasting hrs to days w/concomitant normokalemiaWeakness episodes lasting mins to hrs w/concomitant normo- or hyperkalemiaIdentical to that of the paralytic episodes of hypoPPEpisodic PP, ventricular arrhythmias, prolonged QT interval, characteristic anomalies 2
Age at first attacks Late in 1st decade or in 2nd decadeLate in 1st decade or in 2nd decade1st years of lifeVariable, dependent on onset of thyrotoxicosisLate in 1st decade or in 2nd decade (usually after cardiac events)
Main triggers Rest after exercise, carbohydrate-rich meal, salt intake, stress, coldRest after exercise, carbohydrate-rich meal, salt intake, stress, coldCold; rest after exercise, stress, & fatigue; alcohol; hunger; changes in activity level; potassium in food; specific foodsThyrotoxicosisProlonged rest, rest after exertion
EMG: myotonic discharges NoSomeSomeNoNo
EMG tests Late decrement w/LET (pattern IV, V)Late decrement w/LET (pattern IV, V)Pattern IV, VInitial CMAP ↑ + ↓Variable (CMAP ↑ + ↓, normal CMAP + ↓, etc)
Extramuscular expression NoneNoneNonePossible manifestations of thyrotoxicosisCardiac arrhythmia, dysmorphy
Prevention of paralysis attacks ACZ, DCPACZ, DCPACZ, DCPNormal thyroid functionACZ, DCP
Curative treatment NoneNoneNoneTreatment of thyroid disorderNone
Known causative or susceptibility gene(s) 3 CACNA1S; SCN4A SCN4A SCN4A KCNJ18 KCNJ2
Defective ion channel(s) Cav 1.1;
Nav 1.4;
Kir 6.2
Nav 1.4Nav 1.4Kir 6.2Kir 2.1

ACZ = acetazolamide; CMAP = compound muscle action potential; DCP = dichlorphenamide; LET = long exercise test

1.

OMIM 613239

2.

ATS anomalies include low-set ears, widely spaced eyes, small mandible, fifth-digit clinodactyly, syndactyly, short stature, and scoliosis.

3.

In a cohort of 60 Chinese individuals with primary periodic paralysis, 92.5% of those with a genetic diagnosis had pathogenic variants in CACNA1S, KCNJ2, or SCN4A [Luo et al 2019].

From: Hyperkalemic Periodic Paralysis

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