203. Hypokalemic Periodic Paralysis Flashcards
What is Hypokalemic periodic paralysis (HypoPP)?
A rare hereditary neuromuscular disorder characterized by episodes of skeletal muscle weakness associated with low potassium levels.
It is classified as a skeletal muscle channelopathy.
What are the key features of HypoPP episodes?
Episodes are characterized by:
* Hypokalemia during weakness
* Normokalemia between episodes
* Possible oliguria, diaphoresis, constipation, and sinus bradycardia
Potassium levels typically drop below 3.0 mEq/L during attacks.
What is the prevalence of HypoPP?
Approximately 1:100,000
It is twice as common as hyperkalemic periodic paralysis (HyperPP).
How is HypoPP inherited?
Most cases are hereditary and inherited in an autosomal dominant pattern.
Acquired cases associated with hyperthyroidism have been reported.
What genetic causes are associated with HypoPP?
Approximately two-thirds are caused by:
* A defective dihydropyridine-sensitive calcium channel (type 1)
* A mutation in the skeletal muscle sodium channel SCN4A (type 2)
Penetrance is often incomplete in families with the calcium channel subtype.
What is the gold standard for diagnosing HypoPP?
Genetic testing
It is not available for all possible mutations.
What are provocative tests used in diagnosing HypoPP?
Provocative testing can include:
* Insulin
* Oral glucose bolus
* Intense exercise
These tests are sometimes used in an inpatient setting.
What causes Type 1 HypoPP?
A mutation in a gene encoding the α1-subunit of the dihydropyridine-sensitive calcium channel.
The mechanism affecting potassium flux is not completely understood.
What mutations are associated with Type 2 HypoPP?
Mutations in the α-subunit of the SCN4A gene, which encodes the NaV1.4 protein.
This leads to a reduced myocyte membrane potential.
What are the symptoms of HypoPP attacks?
Attacks typically involve:
* Weakness affecting proximal muscle groups more than distal
* Lower extremities more often involved
* Consciousness maintained during attacks
* Rare respiratory muscle involvement
Myotonia is not a feature of HypoPP.
At what age do symptoms of HypoPP typically begin?
In the first or second decade of life.
Type 2 HypoPP may have a younger age of onset.
What is the best way to prevent HypoPP attacks?
Avoid common triggers and dietary means such as low carbohydrate intake.
Vigorous exercise should also be avoided.
What medications can help reduce the frequency and severity of HypoPP attacks?
Prophylactic medications include:
* Acetazolamide
* Dichlorphenamide
* Spironolactone
* Triamterene
These help by stimulating calcium-activated potassium channels or maintaining higher blood potassium levels.
What is the principal therapy for mild episodes of HypoPP?
Oral or intravenous potassium chloride.
Cardiac monitoring is recommended due to the risk of rebound hyperkalemia.
What are key anesthetic considerations for HypoPP?
Considerations include:
* Avoiding low blood potassium levels
* Minimizing precipitating factors
* Monitoring potassium levels preoperatively
High-carbohydrate meals should be avoided.
