Familial Periodic Paralysis

How periodic paralysis works

Muscle cells contract when electrical signals travel across their membranes through channels for sodium, calcium and potassium. In periodic paralysis, a genetic change in one of these channels makes the muscle membrane unable to fire properly under certain conditions. The muscle becomes temporarily "unexcitable" and weak. Potassium moves into or out of muscle cells during attacks, changing blood potassium levels.

The conditions are usually inherited in an autosomal dominant pattern: a parent with the condition has a 50 in 100 chance of passing it to each child. Some cases arise from a new mutation.

Types of periodic paralysis

Secondary periodic paralysis

A similar picture can be acquired rather than inherited:

• Thyrotoxic periodic paralysis: attacks with low potassium in people with an overactive thyroid, most common in young men of Asian descent. Treating the hyperthyroidism stops the attacks.
• Electrolyte imbalance: low potassium from diuretics, vomiting, diarrhea or kidney disorders, or high potassium from kidney failure or medicines.

Symptoms

• sudden weakness of the arms and legs, usually affecting the legs and proximal muscles (hips and shoulders) most
• attacks often start on waking or after rest following exercise
• face, swallowing and breathing muscles are usually spared, but can be affected in severe attacks
• tingling or aching muscles before attacks in some people
• full or near-full recovery between attacks
• in some people with long-standing disease, permanent weakness of the legs (periodic paralysis myopathy)
• palpitations or irregular heartbeat, especially in Andersen-Tawil syndrome or with extreme potassium levels

People stay fully alert during attacks.

Diagnosis

• Blood potassium during an attack is the most useful single test. It is normal between attacks.
• Thyroid tests to exclude thyrotoxic periodic paralysis.
• ECG during attacks and for Andersen-Tawil syndrome.
• Genetic testing confirms the type in most families.
• Long exercise test on nerve conduction studies shows a characteristic drop in muscle response.
• Exclusion of other causes: urine potassium, kidney function and medicines, plus tests for conditions like myasthenia gravis or Guillain-Barré syndrome if the picture is unclear.

Treatment

During attacks

• Hypokalemic (hypokalemia during attacks): oral potassium salts as advised by your doctor. Avoid IV glucose and salt solutions, which can worsen the attack. Severe attacks are treated in hospital with careful potassium replacement and heart monitoring, as potassium can overshoot.
• Hyperkalemic (hyperkalemia or normal potassium): mild exercise at the start of an attack, eating carbohydrates (such as a sugary drink), and sometimes an inhaled beta-agonist. Severe high potassium is treated in hospital.

Preventing attacks

• Dichlorphenamide, a carbonic anhydrase inhibitor, is FDA-approved to reduce attacks in primary hypokalemic and hyperkalemic periodic paralysis.
• Acetazolamide helps many people with either type, though it can worsen some SCN4A forms of hypokalemic paralysis.
• Potassium-sparing diuretics in hypokalemic forms, and thiazide diuretics in hyperkalemic forms.

Lifestyle

• Hypokalemic: avoid high-carbohydrate and high-salt meals, avoid strenuous exercise followed by rest, and keep a regular routine.
• Hyperkalemic: eat frequent carbohydrate-containing meals, avoid fasting and potassium-rich foods (such as bananas, potatoes and fruit juices), avoid cold, and cool down gently after exercise.
• Carry a medical alert card.

Anesthesia and surgery

Some anesthetic drugs, fasting, IV fluids and cold can trigger severe attacks, and some forms carry a risk of malignant hyperthermia-like reactions. Always tell the anesthesia team about your diagnosis well before surgery.

Outlook

Life expectancy is usually normal. Attack frequency often decreases after middle age, but some people develop permanent muscle weakness. Preventive treatment and trigger avoidance can substantially reduce attacks and may protect long-term strength. Andersen-Tawil syndrome needs ongoing heart monitoring.

Frequently asked questions

What is familial periodic paralysis?

It is a group of rare inherited muscle disorders that cause episodes of muscle weakness or paralysis, usually linked to changes in blood potassium. Strength is normal between attacks. The main types are hypokalemic, hyperkalemic and Andersen-Tawil syndrome.

What triggers a periodic paralysis attack?

Common triggers are rest after strenuous exercise, stress, cold and illness. In the hypokalemic type, carbohydrate-rich or salty meals are typical triggers. In the hyperkalemic type, fasting and potassium-rich foods commonly trigger attacks.

Is periodic paralysis dangerous?

Most attacks are not life-threatening, but severe attacks can affect breathing or cause dangerous heart rhythms due to potassium changes. Some people develop permanent weakness over time. Anesthesia carries specific risks that the surgical team must plan for.

How is periodic paralysis diagnosed?

Measuring blood potassium during an attack is the key clue. Doctors also check thyroid function, perform an ECG, may use a long exercise nerve test, and confirm the type with genetic testing.

Can periodic paralysis be cured?

There is no cure, but treatment works well for most people. Avoiding triggers, taking preventive medicines such as dichlorphenamide or acetazolamide, and treating attacks promptly can greatly reduce how often and how severely attacks happen.