Table 3.

SCN4A-Related Myotonias Compared with Myotonia Congenita (Chloride Channel Myotonia)

Clinical Characteristics in SCN4A-Related MyotoniasCompared w/Myotonia Congenita (Chloride Channel Myotonia)
Paramyotonia congenita (OMIM 168300)Episodes of generalized stiffness in early childhoodAlso observed in MC
Cold sensitivity w/cold-induced severe stiffness usually followed by true weaknessMay be assoc w/some aggravation of stiffness in the cold
Repeated muscle contractions may aggravate stiffness (paradoxic myotonia).Repeated muscle contractions relieve myotonia ("warm-up" phenomenon).
Sodium channel myotonias known as potassium-aggravated myotonia 1 (OMIM 608390)Myotonia may be assoc w/episodes of hyperkalemic periodic paralysis.MC is not assoc w/episodes of periodic paralysis.
Symptoms of sodium channel disorders typically worsen w/potassium ingestion.Not observed in MC
May be assoc w/exercise-induced, delayed-onset myotonia, in which muscle contractions induce myotonia after period of delayContrasts w/the "warm-up" phenomenon seen in MC
Eye closure myotonia is more frequent in sodium channel myotonia.Falls are more frequent in MC.
Painful myotonia is common.Painful myotonia is less common.

MC = myotonia congenita

1.

From: Myotonia Congenita

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