Hyperkalemic periodic paralysis

What it is, symptoms and effects

From: MedlinePlus Genetics, National Library of Medicine

Hyperkalemic periodic paralysis is a condition that causes episodes of extreme muscle weakness or paralysis, usually beginning in infancy or early childhood. Most often, these episodes involve a temporary inability to move muscles in the arms and legs. Episodes tend to increase in frequency until mid-adulthood, after which they occur less frequently in many people with the condition. Factors that can trigger attacks include rest after exercise, potassium-rich foods such as bananas and potatoes, stress, fatigue, alcohol, pregnancy, exposure to hot or cold temperatures, certain medications, and periods without food (fasting). Muscle strength usually returns to normal between attacks, although many affected people continue to experience mild stiffness (myotonia), particularly in muscles of the face and hands.

Most people with hyperkalemic periodic paralysis have increased levels of potassium in their blood (hyperkalemia) during attacks. Hyperkalemia results when the weak or paralyzed muscles release potassium ions into the bloodstream. In other cases, attacks are associated with normal blood potassium levels (normokalemia). Ingesting potassium can trigger attacks in affected individuals, even if blood potassium levels do not go up.

Causes and biological mechanisms

From: MedlinePlus Genetics, National Library of Medicine

Mutations in the SCN4A gene can cause hyperkalemic periodic paralysis. The SCN4A gene provides instructions for making a protein that plays an essential role in muscles used for movement (skeletal muscles). For the body to move normally, these muscles must tense (contract) and relax in a coordinated way. One of the changes that helps trigger muscle contractions is the flow of positively charged atoms (ions), including sodium, into muscle cells. The SCN4A protein forms channels that control the flow of sodium ions into these cells.

Mutations in the SCN4A gene alter the usual structure and function of sodium channels. The altered channels stay open too long or do not stay closed long enough, allowing more sodium ions to flow into muscle cells. This increase in sodium ions triggers the release of potassium from muscle cells, which causes more sodium channels to open and stimulates the flow of even more sodium ions into these cells. These changes in ion transport reduce the ability of skeletal muscles to contract, leading to episodes of muscle weakness or paralysis.

In 30 to 40 percent of cases, the cause of hyperkalemic periodic paralysis is unknown. Changes in other genes, which have not been identified, likely cause the disorder in these cases.

Inheritance and family implications

From: MedlinePlus Genetics, National Library of Medicine

This condition is inherited in an autosomal dominant pattern, which means one copy of the altered gene in each cell is sufficient to cause the disorder.

How common is it?

From: MedlinePlus Genetics, National Library of Medicine

Hyperkalemic periodic paralysis affects an estimated 1 in 200,000 people.

Reported clinical features and what the terms mean

The following findings are associated with this condition in Orphanet. They are not a checklist for diagnosing yourself, and they do not all occur in every affected person. Some are examination, imaging or laboratory findings that cannot be recognised at home.

The frequency labels describe how often a finding was reported among people with the condition in the source. They do not give the chance that a person with that symptom has the condition. Definitions below reproduce HPO terminology; they explain the term, not the likely severity in an individual.

Cerebral palsy · Very frequent (99-80%)

Cerebral palsy describes a group of permanent disorders of the development of movement and posture, causing activity limitation, that are attributed to nonprogressive disturbances that occurred in the developing fetal or infant brain. The motor disorders of cerebral palsy are often accompanied by disturbances of sensation, perception, cognition, communication, and behavior, by epilepsy, and by secondary musculoskeletal problems.

EMG abnormality · Very frequent (99-80%)

Abnormal results of investigations using electromyography (EMG).

Elevated circulating creatine kinase concentration · Very frequent (99-80%)

The activity of creatine kinase in the blood circulation is above the upper limit of normal.

Episodic flaccid weakness · Very frequent (99-80%)

Recurrent episodes of muscle flaccidity, a type of paralysis in which a muscle becomes soft and yields to passive stretching.

Periodic hyperkalemic paralysis · Very frequent (99-80%)

Episodes of muscle weakness associated with elevated levels of potassium in the blood.

Reduced tendon reflexes · Very frequent (99-80%)

A reduction (hyporeflexia) or complete absence (areflexia) of the involuntary muscle contraction normally elicited by a reflex stimulus, such as tapping a deep tendon.

Fasciculations · Frequent (79-30%)

Fasciculations are observed as small, local, involuntary muscle contractions (twitching) visible under the skin. Fasciculations result from increased irritability of an axon (which in turn is often a manifestation of disease of a motor neuron). This leads to sporadic discharges of all the muscle fibers controlled by the axon in isolation from other motor units.

Gait disturbance · Frequent (79-30%)

The term gait disturbance can refer to any disruption of the ability to walk.

Hyperkalemia · Frequent (79-30%)

The concentration of potassium(1+) in the blood circulation is above the upper limit of normal.

Myalgia · Frequent (79-30%)

Pain in muscle.

Myotonia · Frequent (79-30%)

An involuntary and painless delay in the relaxation of skeletal muscle following contraction or electrical stimulation.

Arrhythmia · Occasional (29-5%)

Any cardiac rhythm other than the normal sinus rhythm. Such a rhythm may be either of sinus or ectopic origin and either regular or irregular. An arrhythmia may be due to a disturbance in impulse formation or conduction or both.

Bowel incontinence · Occasional (29-5%)

Involuntary fecal soiling in adults and children who have usually already been toilet trained.

Chest pain · Occasional (29-5%)

An unpleasant sensation characterized by physical discomfort (such as pricking, throbbing, or aching) localized to the chest.

Other findings in the same source

From: Orphanet

Additional reported features include Congestive heart failure (Occasional (29-5%)); Death in early adulthood (Occasional (29-5%)); Death in infancy (Occasional (29-5%)); Feeding difficulties in infancy (Occasional (29-5%)); Flexion contracture (Occasional (29-5%)); Hypertonia (Occasional (29-5%)); Hypokalemia (Occasional (29-5%)); Hyponatremia (Occasional (29-5%)); Malignant hyperthermia (Occasional (29-5%)); Myopathy (Occasional (29-5%)). This is a selected summary, not a complete description of the condition.

Which doctor should you see?

The suggested department for discussing Hyperkalemic periodic paralysis is Neurology, with a neurologist as the relevant type of clinician. General physician / Family Medicine; paediatrician for children. Referral depends on symptoms.

Additional services that may be relevant, depending on the findings, include: Clinical Genetics.

This is an editorial referral starting point. The appropriate clinic depends on the person’s age, symptoms, previous diagnosis and local services. The first clinician can decide whether another specialty or a team is needed; a department label does not confirm the diagnosis.

How to prepare for an assessment

Bring a short timeline of the main symptoms: when they first appeared, whether they are constant or episodic, what seems to change them, and how they affect daily activities. Include previous reports, discharge summaries, current medicines and supplements, allergies, and any relevant family history. A dated record is more useful than trying to match every feature in an online article.

Ask the clinician what is already established and what remains uncertain. If a test is suggested, ask what question it answers, what its limitations are and how the result would change the next step. The information here is not an instruction to arrange every possible test. In children, bring growth, developmental and school information if it is relevant to the concern.

• Which nervous-system findings help explain the symptoms?
• Would an assessment of walking, communication or daily function be helpful?
• Are rehabilitation or other specialist services relevant?

Treatment discussions and follow-up

The material gathered for this draft does not provide a complete condition-specific treatment pathway for Hyperkalemic periodic paralysis. That gap does not mean that treatment is unavailable. A clinician needs to establish the diagnosis and review current guidance before recommending medicines, procedures, rehabilitation or other support.

Before leaving the appointment, clarify the next review date, who will communicate results, and whom to contact if the situation changes. Discuss difficulties with sleep, work, school, mobility, eating or emotional wellbeing when these are relevant. Practical support may require coordination between the treating clinician and other services.

The collected references do not establish a complete prevention or long-term outlook section for this entry. Missing information should not be interpreted as proof that prevention is impossible or that a particular outcome is inevitable. Ask what is known for the exact subtype, stage and personal circumstances, and which uncertainties remain.

When to seek emergency help

Severe breathing difficulty, collapse, new stroke-like symptoms, a seizure that is prolonged or repeated without recovery, uncontrolled major bleeding, or an immediate risk of self-harm require emergency help. In India, call 112 or reach the nearest emergency department. This is a general, non-exhaustive warning list; it is not a condition-specific triage tool.