Reversible quadriplegia and Mobitz type II block in hypokalemic periodic paralysis: a case report on the multifaceted approach to rare metabolic disorders

Abstract Background Hypokalemic periodic paralysis (HPP) is a rare channelopathy causing episodic muscle weakness, often linked to thyrotoxicosis. While neuromuscular symptoms predominate, cardiac complications such as arrhythmias are infrequent, and higher-degree atrioventricular (AV) blocks like Mobitz type II are exceptionally rare. Case presentation A 37-year-old male with a history of pulmonary thromboembolism and asthma presented with acute quadriplegia. Examination revealed 0/5 muscle strength in all limbs and absent deep tendon reflexes. Laboratory findings confirmed severe hypokalemia (serum potassium: 1.7 mmol/L). An electrocardiogram (ECG) showed a 3:1 Mobitz type II AV block, despite no cardiac symptoms. Thyroid function tests indicated hyperthyroidism (suppressed thyroid-stimulating hormone, elevated T3/T4), leading to a presumptive diagnosis of thyrotoxic HPP. Intravenous potassium chloride was administered, normalizing potassium levels within eight hours. Post-treatment, muscle strength returned to 5/5, reflexes normalized, and the AV block resolved on follow-up ECG. Conclusions This case represents a rare occurrence of Mobitz type II AV block in HPP, illustrating its potential to cause both severe neuromuscular and cardiac conduction abnormalities, even in hemodynamically stable patients. The complete resolution of quadriplegia and the AV block following potassium supplementation highlights the critical role of rapid electrolyte correction. Preventing recurrence requires addressing the underlying thyrotoxicosis through a multidisciplinary approach involving cardiology and endocrinology. These findings underscore the importance of early diagnosis and intervention when managing complex metabolic disorders with unexpected cardiac manifestations.