Makindo Medical Notes

Related Subjects: Hyperkalaemia | ECG - Hyperkalaemia | Hypokalaemia | Hyperkalaemic and Hypokalaemic Periodic Paralysis | Resuscitation - Advanced Life Support | Action Potential

Both hypokalaemic and hyperkalaemic paralysis are not caused by defects in potassium channels but rather in calcium and sodium channels, respectively. There are three distinct forms of periodic muscle paralysis related to potassium dysregulation.

1️⃣ Hypokalaemic Periodic Muscle Paralysis

• Genetic Defect: Autosomal dominant mutation in calcium channels (CACNA1S gene).
• Precipitating Factors: High carbohydrate meals, heavy exertion, thyrotoxicosis.
• Clinical Presentation: Weakness after meals or exercise, lasting for days. May involve bulbar muscles (e.g., dysphagia). Onset usually in teenage years, improves with age.
• Treatment: Low carbohydrate, low sodium diet; avoid strenuous exercise; cautious use of oral potassium supplements.

2️⃣ Hyperkalaemic Periodic Muscle Paralysis

• Genetic Defect: Autosomal dominant sodium channel defect (SCN4A gene).
• Precipitating Factors: Rest after exercise, fasting, oral potassium intake.
• Clinical Presentation: Episodes of weakness lasting 1–2 hours, starting in childhood/teenage years. Weakness improves with mild exercise. Diagnosis can be confirmed with potassium provocation testing.
• Treatment: Acute attacks managed with IV calcium gluconate or IV furosemide. Prevent with dietary modifications and potassium avoidance.

3️⃣ Normokalaemic Periodic Muscle Paralysis

• Genetic Defect: Related to sodium channel mutations.
• Precipitating Factors: Similar triggers to the hyperkalaemic form.
• Clinical Presentation: Similar to hyperkalaemic attacks, but potassium levels remain normal during episodes.
• Treatment: Acetazolamide is the drug of choice to reduce frequency of attacks.

Cases — Hyperkalaemic & Hypokalaemic Periodic Paralysis

• Case 1 — Hyperkalaemic Periodic Paralysis (Trigger: Rest After Exercise) 🏃‍♂️: A 14-year-old boy presents with recurrent episodes of muscle weakness lasting 1–2 hours. Attacks often occur after vigorous exercise followed by rest. During one episode, exam shows flaccid weakness of all limbs; reflexes are reduced. Serum potassium = 6.0 mmol/L. Diagnosis: Hyperkalaemic periodic paralysis (sodium channel mutation). Management: Mild exercise during prodrome, carbohydrate intake to lower potassium, thiazide diuretics or acetazolamide for prevention.
• Case 2 — Hypokalaemic Periodic Paralysis (Trigger: High-Carb Meal) 🍝: A 20-year-old man wakes up with sudden inability to move his legs after a large pasta meal the night before. Exam: symmetrical flaccid paralysis, absent reflexes, preserved sensation. Serum potassium = 2.1 mmol/L. Diagnosis: Hypokalaemic periodic paralysis (calcium channel mutation). Management: IV potassium replacement (careful monitoring); long-term acetazolamide prophylaxis; trigger avoidance.
• Case 3 — Thyrotoxic Hypokalaemic Periodic Paralysis (Asian Male) 🧬: A 28-year-old man of Chinese origin presents with recurrent episodes of limb weakness, particularly after heavy meals and rest. Exam: proximal weakness, reduced reflexes. Bloods: K+ = 2.4 mmol/L, TSH suppressed, free T4 elevated. Diagnosis: Thyrotoxic periodic paralysis (hypokalaemic). Management: Correct hypokalaemia acutely; initiate antithyroid therapy (carbimazole); beta-blocker (propranolol) for acute symptom relief; long-term definitive treatment for thyrotoxicosis.

Teaching Commentary ⚡

Periodic paralyses are channelopathies — rare inherited or acquired disorders of ion channels, causing episodic flaccid weakness: - Hyperkalaemic: brief episodes (minutes–hours), often triggered by rest after exercise or fasting; sodium channel mutation (SCN4A). - Hypokalaemic: longer episodes (hours–days), triggered by carbohydrate-rich meals, rest after exertion; calcium channel mutation (CACNA1S). - Thyrotoxic hypokalaemic: common in Asian men; due to increased Na⁺/K⁺ ATPase activity from excess thyroid hormone. Key principle: potassium level during attack distinguishes type. Management = trigger avoidance, acute correction of potassium, and prophylactic carbonic anhydrase inhibitors (acetazolamide/dichlorphenamide). Thyrotoxic cases need thyroid treatment.