Group of hereditary diseases of the ion channels for Na, K or Ca (or chanellopathies). 

They are currently classified according to kalemia at the time of the attack of muscle paralysis: 

• familial hypokalemic paralysis [MIM 170 400, 613 345] (Westphall disease): autosomal dominant transmission of mutations. Type 1 [MIM 170 400]: mutation of the CACN1AS gene (1q31-q32)coding for the α1 subunit of the dihydropyridine receptor at the Ca++  channel of the muscle. Type 2 [MIM 613 345]: mutation of the SCNA4 gene (17q23.3) coding for the subunit α of the Nav1.4 channel of the muscle. Some cases are due to a mutation of the ATP1A2 gene (1q23.2) or to a mutation of the KCNE3 gene (11p13.4) [MIM 170 400] coding for the voltage-dependent K channel Isk. 

Often attack of asymmetric flaccid paralysis lasting from a few hours to a few days. Oculomotor muscles, swallowing and the diaphragm are spared. Hypokalemia is important and can have a lethal risk because of cardiac dysrhythmias. The crisis can be caused by stress, cold, a carbohydrate-rich meal, an infection, childbirth labor or rest after exercise. A documented case of clinical crisis of malignant hyperthermia with equivocal response to the muscle contracture tests has been reported: it may be a hypermetabolic crisis due to dysregulation of intramuscular Ca metabolism or an associated mutation of the RYR1 gene. 
Chronic treatment: acetazolamide (only in type 1, as this treatment can lead to hypokalemia in type 2), oral K supplements.

• familial hyperkalemic paralysis [MIM 170 500] (Gamstorp disease, Gamstorp episodic adynamia): autosomal dominant transmission of a mutation of the SCN4A gene (17q13.1-q13.3) coding for the α subunit of the muscle Na v1.4 channel. Onset in early childhood: attacks of muscle weakness at rest after physical exercise. Attacks of paralysis last from a few minutes to a few hours and are generally located to the group of muscles at rest after exercise. The crisis can be stopped if the patient starts moving its muscles when he feels the premonitory signs (acroparesthesies) of an attack. There may be dysphagia and respiratory weakness but the oculomotor muscles are spared. The kalemia increases rapidly during the crisis that is triggered by cold, hypoglycemia (prolonged fasting), stress. This condition is sometimes associated (45 %) with myotonic (see congenital paramyotonia) signs between attacks of paralysis.
• familial normokalemic paralysis [MIM 170 600] (periodic paralysis type 3): it could be a variant of the hyperkalemic forms the attacks of which last longer.

Anesthetic implications: 

Avoidance of:

- hypothermia and contact with cold objects;

- stress;

- succinylcholine;

Monitoring of the EKG for signs of hyper- or hypokalemia, monitoring of the K blood levels.

1) in hypokalemic form: [K+] target: 4 mmol/l; avoid glucose intake and beta-adrenergic agents, and provide K supplements perioperatively; low risk of malignant hyperthermia or hypermetabolic crisis. In the event of delivery or caesarean section, misoprostol is the uterotonic of choice.

2) in case of hyper- or normokalemic form: avoid prolonged fasting (infusion of a glucose-containing electrolytic solution  should be started at the same time as preoperative fasting) and K supplements; preoperative (diuretic) K depletion can be useful. Diuretics should not be stopped in the preoperative period. Check plasma K level: the patient's 'paralysing' threshold is often within the normal limits.

Since the facial muscles are often spared during the attacks of paralysis, it is recommended to monitor neuromuscular blockade at this level. Avoid succinylcholine which can cause a generalized contraction followed by prolonged paralysis,  

References : 

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Updated: March 2025