Makindo Medical Notes

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

⚡ Hypokalaemic Periodic Paralysis is an autosomal dominant channelopathy caused by a mutation in a voltage-gated calcium channel. 🍚 Patients typically develop generalised weakness after a high-carbohydrate meal. 👨‍👩‍👧 Family history may include similar episodes. 🧪 A provocation test with oral glucose can support diagnosis, and potassium supplementation often relieves symptoms.

About

• ⚡ Most common form of periodic paralysis syndromes.
• 🧬 Inherited in an autosomal dominant pattern due to calcium channel mutation.

Aetiology

• 🔥 Associated with thyrotoxicosis.
• 🌏 More prevalent in Southeast Asia.

Precipitating and Relieving Factors

• 🚩 Precipitating Factors:
  • 💊 Potassium-lowering diuretics (e.g., thiazides).
  • 🍝 High-carbohydrate or 🧂 high-sodium meals.
  • 💉 IV glucose or IV saline.
• ✅ Relieving Factor: Potassium supplementation restores strength during attacks.

Clinical Features

• 💪 Episodes of generalised weakness after carbohydrate-rich meals.
• 👦 Onset often in teenage years, improving with age.
• 🗣️ Weakness may involve bulbar muscles → dysphagia.
• ⏳ Attacks last several hours, often early morning or after rest following exertion.
• 👨‍👩‍👧 Family history frequently positive.

Investigations

• 🧪 Serum Potassium: < 3.0 mmol/L during an attack.
• 🧬 Genetic Testing: To confirm calcium channel mutation.

Management

• 🥗 Diet: Low-carbohydrate, low-sodium diet to reduce risk of attacks.
• 🏃 Exercise: Avoid excessive exertion (attacks often occur after rest).
• 💊 Medications:
  • Acetazolamide to reduce attack frequency.
  • Potassium-sparing diuretics (e.g., triamterene, spironolactone) in some cases.

Cases — Hypokalaemic Periodic Paralysis (HypoPP)

• Case 1 — Post-Exercise Attack 🏃: A 19-year-old male athlete develops sudden weakness in both legs the morning after an intense gym session. He is unable to stand unaided. Sensation is preserved, reflexes reduced. Serum potassium = 2.3 mmol/L. Diagnosis: Hypokalaemic periodic paralysis triggered by rest after exertion. Management: IV potassium chloride infusion (monitored); long-term acetazolamide prophylaxis.
• Case 2 — Carbohydrate-Induced Paralysis 🍚: A 21-year-old student experiences recurrent episodes of flaccid limb weakness after large high-carbohydrate meals. During one attack, exam shows profound proximal weakness in all four limbs, with intact cranial nerves. Serum potassium = 2.0 mmol/L. Diagnosis: HypoPP due to calcium channel mutation (CACNA1S). Management: Oral potassium supplementation; dietary trigger avoidance; prophylactic carbonic anhydrase inhibitor.
• Case 3 — Thyrotoxic Hypokalaemic Paralysis 🌡️: A 28-year-old Chinese man presents with recurrent limb weakness, worse at night after alcohol binges. Exam: flaccid paralysis, diminished reflexes, but preserved sensation. Serum potassium = 2.2 mmol/L; TFTs show suppressed TSH, elevated free T4. Diagnosis: Thyrotoxic hypokalaemic periodic paralysis. Management: Acute K⁺ replacement; non-selective β-blocker (propranolol) for acute control; definitive treatment of thyrotoxicosis with antithyroid drugs ± radioiodine or surgery.

Teaching Commentary 🧠

HypoPP is a channelopathy (often CACNA1S or SCN4A mutation) characterised by recurrent episodes of flaccid weakness with low serum potassium. 🔑 Triggers: carbohydrate-rich meals, rest after exercise, alcohol, stress. - Attacks last hours–days, sparing sensation and consciousness. - Thyrotoxic variant is common in Asian men and reversible with thyroid treatment. 🧪 Diagnosis: low K⁺ during attack, exclusion of secondary causes (thyroid disease, renal tubular acidosis, diuretic abuse). ⚕️ Management: acute potassium replacement (oral preferred unless severe), avoidance of triggers, acetazolamide/dichlorphenamide prophylaxis, and thyroid treatment if thyrotoxic.