Periodic paralysis
Human genetic disease causing episodes of muscle weakness or paralysis
Periodic paralysis | |
---|---|
Synonyms | Myoplegia paroxysmalis familiaris |
Pronounce | N/A |
Specialty | N/A |
Symptoms | N/A |
Complications | Respiratory failure, cardiac arrhythmia |
Onset | Typically childhood or adolescence |
Duration | Lifelong |
Types | Hypokalemic periodic paralysis, Hyperkalemic periodic paralysis, Paramyotonia congenita, Andersen–Tawil syndrome |
Causes | Genetic mutations affecting ion channels |
Risks | Family history, exercise, carbohydrate-rich meals, stress |
Diagnosis | Genetic testing, electromyography, blood tests for potassium |
Differential diagnosis | Myasthenia gravis, thyrotoxic periodic paralysis, Guillain–Barré syndrome |
Prevention | Avoidance of triggers (e.g. high-carb meals, strenuous activity) |
Treatment | Lifestyle modification, potassium supplements, carbonic anhydrase inhibitors |
Medication | Acetazolamide, dichlorphenamide, potassium chloride |
Prognosis | Variable; symptoms may be controlled with appropriate management |
Frequency | Rare |
Deaths | Rare, may occur with severe cardiac involvement |
Periodic paralysis is a group of rare genetic disorders characterized by recurring episodes of muscle weakness or paralysis. These episodes are often associated with abnormal levels of potassium in the blood, although some cases show normal potassium levels during attacks. Periodic paralysis is considered a form of channelopathy—a disorder caused by dysfunctional ion channels in muscle cell membranes.
Although primarily genetic, a similar condition known as thyrotoxic periodic paralysis may occur in individuals with hyperthyroidism, particularly in people of Asian or Latin American descent.
Types[edit | edit source]
Periodic paralysis disorders are typically inherited in an autosomal dominant fashion and can vary widely in expression and severity among individuals. The major forms include:
Hypokalemic periodic paralysis[edit | edit source]
- Caused by mutations in the CACNA1S or SCN4A gene.
- Episodes are triggered by a drop in blood potassium levels, often after exercise or high-carbohydrate meals.
- Common symptoms include weakness in the limbs, typically occurring upon waking or after rest.
Hyperkalemic periodic paralysis[edit | edit source]
- Caused by mutations in the SCN4A gene.
- Characterized by episodes triggered by elevated potassium levels or fasting.
- Muscle stiffness (myotonia) may accompany episodes, and attacks tend to be shorter than those of the hypokalemic form.
Paramyotonia congenita[edit | edit source]
- A related condition often co-occurring with hyperkalemic periodic paralysis.
- Characterized by muscle stiffness and weakness triggered by cold exposure or exercise.
- Unlike the other types, symptoms may worsen during activity.
Andersen–Tawil syndrome[edit | edit source]
- A rare and complex form of periodic paralysis caused by mutations in the KCNJ2 gene.
- Features include periodic paralysis, cardiac arrhythmias, and distinctive physical characteristics such as:
Scoliosis Clinodactyly Syndactyly Micrognathia Low-set ears
- Potassium levels can be low, high, or normal during episodes.
- Estimated to affect fewer than 100 individuals globally.
Signs and symptoms[edit | edit source]
Symptoms vary depending on the type but generally include:
- Sudden muscle weakness or paralysis lasting from minutes to hours
- Muscle stiffness or myotonia
- Triggering by rest after exercise, high-carb meals, cold exposure, or stress
- In some cases, difficulty breathing or heart rhythm abnormalities during severe attacks
Cause[edit | edit source]
Periodic paralysis is most often caused by mutations in genes that encode ion channels, especially those involving sodium (Na⁺), calcium (Ca²⁺), and potassium (K⁺) regulation:
- Mutations in the SCN4A gene affect sodium channels in skeletal muscle.
- Mutations in the CACNA1S gene affect calcium channels.
- Mutations in the KCNJ2 gene affect potassium channels, as seen in Andersen–Tawil syndrome.
These mutations disrupt the normal flow of ions into and out of muscle cells, impairing their ability to contract and relax properly.
Triggers[edit | edit source]
Common triggers for periodic paralysis episodes include:
- Carbohydrate-rich meals
- Fasting
- Rest after strenuous exercise
- Emotional stress
- Cold temperatures
- Certain medications (e.g., glucocorticoids, beta-adrenergic agonists)
Diagnosis[edit | edit source]
Diagnosis is typically based on:
- Clinical history of episodic muscle weakness or paralysis
- Serum potassium measurement during an attack
- Electromyography (EMG) testing to assess muscle response
- Genetic testing to identify causative mutations
- Provocative testing, such as glucose-potassium challenge, may be used in specialized centers
Treatment[edit | edit source]
Management focuses on prevention and acute treatment of attacks:
Preventive measures[edit | edit source]
- Avoidance of triggers (e.g. certain foods, extreme temperatures)
- Low-carbohydrate diet
- Regular, moderate exercise
Medications[edit | edit source]
- Potassium chloride (oral or IV) for hypokalemic attacks
- Carbonic anhydrase inhibitors (e.g., acetazolamide, dichlorphenamide) may help reduce attack frequency
- Beta-blockers in some cases of thyrotoxic periodic paralysis
Acute management[edit | edit source]
- Careful administration of potassium (oral or IV) or glucose depending on potassium levels
- Close monitoring of cardiac and respiratory function during severe attacks
Prognosis[edit | edit source]
With appropriate management, many individuals can reduce the frequency and severity of attacks. However, in some cases, long-term muscle weakness (permanent myopathy) may develop. Patients with cardiac involvement, especially in Andersen–Tawil syndrome, require ongoing monitoring and treatment due to risk of serious arrhythmias.
See also[edit | edit source]
- Channelopathy
- Myopathy
- Thyrotoxic periodic paralysis
- Muscle weakness
- Andersen–Tawil syndrome
- Potassium
External links[edit | edit source]
- Periodic Paralysis – Genetic and Rare Diseases Information Center (GARD)
- Periodic Paralysis International
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