Objective:

Report a case of thyrotoxic periodic paralysis.

Background:

Thyrotoxic periodic paralysis (TPP) is a disorder characterized by attacks of proximal muscle weakness involving trunk and limbs but sparing cranial muscles. Serum potassium levels are often low during attacks, and attacks resolve with potassium repletion. The proposed mechanism is secondary to rapid intracellular shifting of potassium triggered by excess thyroid hormones, adrenergic stimulation, or hyperinsulinemia. The most effective treatment is control of the underlying hyperthyroidism. Although not familial, it is frequently seen in Asian and Hispanic males, likely due to population-specific genetic variants affecting potassium channel function and sex-related physiological differences in potassium regulation. Certain genetic variants confer genetic susceptibility (e.g., mutations in KCNJ18 encoding Kir2.6), with environmental triggers, including high-carbohydrate meals and rest after prolonged exercise, playing an additional role.

Design/Methods:

NA

Results:

A 39-year-old East Asian male presented with insidious onset of intermittent proximal weakness progressing over a month to involve his hip and shoulder girdle muscles. He first became alarmed when he could not rise from a seated position after an extended period of playing video games. He reported four similar episodes in the past month without complete return to baseline strength and noted some correlation with high-carbohydrate meals. Physical examination demonstrated diminished proximal with preserved distal muscle strength in all extremities, hyporeflexia in bilateral patellae, normal sensory exam, intact extraocular movement, and no nystagmus or ptosis. Serum testing revealed mild-moderate hypokalemia, low TSH, elevated T3 and free T4. After repletion of potassium, the patient’s weakness resolved. He was started on methimazole and atenolol with endocrinology follow-up.

Conclusions:

We encourage clinicians to obtain a careful history of attack timeline in patients presenting with periodic weakness and to evaluate thyroid function even in the absence of hyperthyroid symptoms. Patients with TPP may have normal potassium levels between attacks.