Familial Hypokalemic Periodic Paralysis

Introduction: Periodic Paralysis (PP) is a rare neuromuscular disease related to a defect in muscle ion channels, characterized by sporadic episodes of painless muscle weakness that can be precipitated by vigorous exercise, prolonged fasting, or carbohydrate-rich meals. PP is classified as hypokalemic when episodes occur associated with low levels of potassium in the blood. The crises start in late childhood or early adolescence and vary in frequency and duration. Treatment during the acute phase is administration of potassium chloride.

Case Report: A 12-year-old female adolescent appealed to the emergency department due to sudden onset of tetraparesis. She had no difficulty breathing nor signs of respiratory distress. Cardiac, pulmonary and abdomen examination was normal. Conscious and oriented in time and space. Neurological examination showed grade II muscle strength in the lower limbs and grade III in the upper limbs. Osteotendinous reflexes were absent. Facial mimic was present.

Upon this presentation the mother promptly revealed a familiar history of periodic hypokalemic paralysis affecting several members.

Blood analysis showed an isolated severe hypokalemia of 1,7-2,0 mmol/L. ECG showed prolonged PR interval, mild ST depression, prominent U waves.

Slow correction of potassium was promptly started with gradual recovery of muscle strength and ECG stabilization. She was discharged 20 hours after therapy onset and medicated at home with daily acetazolamide and potassium chloride if onset of symptoms. Genetic study was started for índex familial mutations.

Conclusion: Periodic familial paralyzes are rare conditions, the most frequent being the hypokalemic form. The diagnosis of PP can be confirmed by genetic tests, which are recommended as first line when there is an intermediate to high degree of clinical suspicion. This case report is intended to emphasize the importance of the clinical history and a complete physical examination on diagnosis. Treatment should not be delayed. Genetic family counseling should be offered.