Endocrine Abstracts

A 35 year old Asian man presented to the emergency department on several occasions with episodes of severe muscle weakness, affecting his arms and legs, to the point he was unable to walk or stand. He was found to be hypokalaemic on both occasions, at 2.3mmol/l and 3.0mmol/l respectively, and his weakness gradually improved with potassium replacement. He gave a history of two years of intermittent weakness and stiffness of the limbs which typically occurred at night or after long periods of rest. Initially they resolved spontaneously within minutes but the attacks became increasingly severe, lasting hours, to the point he was unable to mobilise. He reported a recent history of weight loss, tremor, palpitations and significant heat intolerance. He was found to be thyrotoxic with a suppressed TSH, free T4 39.4 pmol/l and free T3 14.4 pmol/l. His TSH receptor antibodies were positive at 4.0 IU/l and the diagnosis of Grave’s disease was made. He was commenced on Carbimazole 40 mg and Propanolol. Looking back at his previous results he had subclinical hyperthyroidism at the time when his symptoms of weakness first presented, but no treatment was given at that stage. Given the presentation of acute painless muscle weakness, in the presence of hypokalaemia and thyroxicosis, a diagnosis of thyrotoxic periodic paralysis was made. This is an extremely rare condition which is most commonly caused by Grave’s disease and occurs more frequently in Asian men between the ages of 20 and 40. It is potentially life-threatening and prompt correction of hypokalaemia is essential in the acute phase. Resolution of the attacks occurs with curative treatment of the thyrotoxicosis, either with surgery or radioiodine ablation. Our patient’s thyroid function rapidly normalised and his episodes of weakness completely resolved. The Carbimazole was titrated down and his TSH fell below the normal range. This caused his symptoms of weakness to transiently return. Due to his young age and the severity of his weakness in the context of thyrotoxicosis we recommended proceeding to curative thyroidectomy. The risk of radiation induced thyroiditis causing severe paralysis was deemed to be unacceptable.