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Hyperkalemic Periodic Paralysis (HyperKPP): Brief Attacks of Weakness With Muscle Stiffness
An episodic sodium channel disorder causing short attacks of weakness with high or normal potassium, often accompanied by myotonia between attacks. SCN4A genetic testing, EMG, and trigger-based prevention at KIMS Neuroscience, Secunderabad, Hyderabad.
G72.3
SCN4A
Minutes to Hours
Myotonia
Hyperkalemic periodic paralysis (HyperKPP) is an episodic skeletal muscle channelopathy caused by mutations in the SCN4A gene, which encodes the muscle sodium channel. It causes brief attacks of weakness or paralysis associated with elevated or normal serum potassium. Attacks are typically shorter than in hypokalemic periodic paralysis — minutes to hours — and are triggered by fasting, cold exposure, or rest after exercise. Myotonia (muscle stiffness) is frequently present between attacks and may be the first complaint. Paramyotonia congenita is a related sodium channel condition in which stiffness and weakness worsen with cold. Diagnosis rests on SCN4A genetic testing and EMG, which shows myotonia on needle examination and characteristic changes with exercise and temperature. Treatment includes thiazide diuretics, carbohydrate intake during attacks, and mexiletine for myotonia.
- What it is
- An inherited muscle sodium channel disorder (SCN4A) causing brief episodes of weakness with high or normal potassium.
- Typical attack
- Shorter than hypokalemic attacks — minutes to hours. Often begins during rest after exercise, with fasting, or on cold exposure. Strength returns between attacks.
- Myotonia
- Muscle stiffness is common between attacks and may be the first symptom. Paramyotonia congenita, a related condition, worsens with cold.
- Diagnosis at KIMS
- Serum potassium during an attack · Needle EMG showing myotonia · Exercise and temperature-based EMG protocols · SCN4A genetic testing.
- Treatment
- Thiazide diuretics for prevention · Carbohydrate intake at the onset of an attack · Mexiletine for troublesome myotonia · Trigger avoidance.
- Contact KIMS
- Outpatient: 040-44885000 · Emergency: 040-46324365 · No referral required.
| Fact | Details |
|---|---|
| Condition | Hyperkalemic Periodic Paralysis (HyperKPP) |
| ICD-10 | G72.3 |
| Genetics | SCN4A (skeletal muscle sodium channel) mutations · Usually autosomal dominant |
| Attack pattern | Brief — minutes to hours · Elevated or normal potassium · Normal strength between attacks |
| Triggers | Fasting · Cold exposure · Rest after exercise · Potassium-rich foods |
| Associated features | Myotonia between attacks · Paramyotonia congenita is a related, cold-sensitive condition |
| Diagnosis | SCN4A genetic testing · Needle EMG (myotonia) · CMAP changes with exercise and temperature |
| Treatment | Thiazide diuretics · Carbohydrate intake during attacks · Mexiletine for myotonia · Trigger avoidance |
About This Condition
A Sodium Channel That Will Not Close Properly
In hyperkalemic periodic paralysis, a faulty muscle sodium channel lets too much sodium flow into the muscle fibre under certain conditions. The membrane becomes persistently depolarised and, paradoxically, unable to fire — producing weakness. In milder form, the same channel fault causes repetitive firing, which is felt as myotonic stiffness.
That shared mechanism explains why stiffness and weakness so often occur together in this condition. Many patients first notice difficulty relaxing their grip or stiffness in the face and hands, and only later recognise the brief attacks of weakness.
Compared with hypokalemic periodic paralysis, attacks are shorter and occur with high or normal potassium, and they are provoked by different triggers — fasting, cold, and rest after exercise rather than carbohydrate-rich meals. The distinction matters because the treatments differ.
Book a Consultation
Speak directly with our neuromuscular team — potassium measurement during attacks, needle EMG and exercise/temperature protocols, SCN4A genetic testing, preventive therapy, and mexiletine with ECG monitoring for myotonia. No referral required. Monday to Saturday.
040-44885000Emergency line: 040-46324365Recognising Hyperkalemic Periodic Paralysis
Brief attacks
Episodes of weakness lasting minutes to hours, often starting in the legs, with full recovery between attacks. Attacks may begin in childhood.
Triggers
Rest after exercise, fasting or a missed meal, cold exposure, and potassium-rich foods are the typical provoking factors.
Myotonia
Muscle stiffness — difficulty releasing a grip, opening the eyes after squeezing them shut, or stiffness in the face and hands — is common between attacks.
Paramyotonia congenita
A related sodium channel condition in which stiffness paradoxically worsens with repeated movement and with cold, and cold exposure can bring on weakness.
Potassium levels
Potassium is elevated or high-normal during attacks. It may be normal, so a normal result does not exclude the diagnosis.
Heart rhythm
High potassium can affect heart rhythm, so attacks with palpitations need prompt assessment with an ECG.
Diagnosis at KIMS
Diagnosis at KIMS
Clinical history and examination
The timing, duration, and triggers of attacks, the presence of myotonia between attacks, and any family history of similar episodes.
Potassium during an attack
Measured promptly during an episode. Elevated or high-normal potassium supports the diagnosis.
EMG
Needle EMG shows myotonic discharges. Specialised exercise and temperature-based protocols show characteristic changes in compound muscle action potentials.
SCN4A genetic testing
Confirms the diagnosis and supports family counselling, as the condition is usually autosomal dominant.
Treatment
Treatment and Prevention
Thiazide Diuretics
Thiazide diuretics lower potassium and reduce the frequency of attacks in many patients.
Treatment is adjusted with monitoring of blood potassium and sodium.
Carbohydrate at Onset
Taking carbohydrate at the first sign of an attack helps shift potassium into cells and can shorten or abort the episode.
Light exercise at onset helps some patients.
Mexiletine
Mexiletine reduces troublesome myotonic stiffness.
An ECG is performed before starting and during treatment to assess cardiac conduction.
Trigger Avoidance
Regular meals without prolonged fasting, avoiding cold exposure, and avoiding potassium-rich foods.
Gradual cool-down rather than abrupt rest after strenuous exercise.
Related Conditions
Hyperkalemic periodic paralysis is one of the channelopathies evaluated and managed at KIMS Neuroscience:
FAQs
Frequently Asked Questions
Short spells of weakness after exercise or a missed meal. Stiff hands that are slow to let go. Hyperkalemic periodic paralysis is a treatable sodium channel disorder — diagnosed and managed at KIMS Neuroscience, Hyderabad.
At KIMS Neuroscience, Secunderabad, Hyderabad, hyperkalemic periodic paralysis is diagnosed with potassium measurement during attacks, needle EMG with exercise and temperature protocols, and SCN4A genetic testing — then managed with thiazide prophylaxis, carbohydrate at attack onset, mexiletine for myotonia, and trigger avoidance. Call 040-44885000. No referral required.
International enquiries: info@kimsneurosciences.com