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A 38 year old man presented with a history of episodic lower limb weakness lasting a few hours. The weakness was predominantly proximal and was preceded by cramps in the affected muscles. There were two such attacks separated by a one month period. He was perfectly normal in between the episodes. The weakness was unrelated to exertion or meals. The upper limbs, eyes, face, tongue, pharynx, larynx, diaphragm, and sphincters were spared. There were no sensory abnormalities. He did not have vomiting or diarrhoea, nor was he on any medication. He had had no major illness in the past. No other family member had a similar illness. His appetite was good and there was no change in his weight in recent years. His sleep was normal, so were his bowel and bladder habits. He did not have any addictions. On physical examination, the patient was afebrile and nervous. He had a heart rate of 120 beats/min and a blood pressure of 170/70 mm Hg.
During the attack, there was a flaccid paraparesis with depressed tendon jerks. In the interattack period, strength was normal and the reflexes were brisk. His serum potassium concentration during the attack was 3.2 mmol/l, and after recovery 4.0 mmol/l (reference range 3.5–5.0 mmol/l). The concentration in urine was normal. Other electrolyte values were within normal limits. Further studies were performed to establish the aetiology.
What is the diagnosis?
How did we confirm it?
How should the patient be managed?
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