Rare case of thyrotoxic Periodic Paralysis reported in NEJM

The case is published in the New England Journal of Medicine.

Thyrotoxic periodic paralysis is a condition that is characterized by episodes of muscle weakness associated with hyperthyroidism.

The authors studied the case of a 25-year-old man who presented to the emergency department with a sudden onset of weakness in his arms and legs. He reported a 3-month history of intermittent arm and leg weakness, palpitations, trembling, and insomnia.

On a thorough examination, he had a heart rate of 107 beats per minute, a palpable goiter, and an inability to lift his arms or legs. Laboratory studies were advised which revealed a potassium level of 1.6 mmol per liter (reference range, 3.5 to 5.0), a phosphate level of 0.5 mmol per liter (reference range, 0.8 to 1.5), a thyrotropin level of less than 0.01 μU per milliliter (reference range, 0.40 to 3.80), a free triiodothyronine level of 2.21 ng per deciliter (reference range, 0.26 to 0.44), and a free thyroxine level of 7.8 ng per deciliter (reference range, 0.9 to 1.6).

Furthermore, supplementation with potassium and phosphate was initiated. When the potassium level had increased to 1.9 mmol per liter, he was able to lift his arms but was still unable to lift his legs.

However, when the potassium level was 3.3 mmol per liter (approximately 4 hours after the initial examination), he was able to fully lift his arms and legs.

Therefore, the researchers confirmed a diagnosis of thyrotoxic periodic paralysis. The episodes usually are typically associated with severe hypokalemia.

The treatment with methimazole and propranolol was then initiated. At follow-up 3 weeks later, he reported no arm or leg weakness, palpitations, trembling, or insomnia.

The authors laid out the laboratory tests which further revealed elevated levels of thyrotropin-receptor antibodies (>40 IU per liter [reference value, <1.0]), thereby confirming a diagnosis of Graves' disease.

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Thyrotoxic Periodic Paralysis. N. Engl. J. Med 2021 May 13;384(19)e71, M Fralick, S Sarma