Which clinical feature best differentiates thyroid storm from myxedema coma?

• A. Fever and tachycardia favor thyroid storm; hypothermia and coma favor myxedema coma
• B. Hyponatremia favors thyroid storm
• C. Hypotension favors thyroid storm
• D. Hypercalcemia favors thyroid storm

Answer: (B)

The key idea is that thyroid storm and myxedema coma present at opposite ends of thyroid function, so features that signal an acute thyrotoxic, hypermetabolic state help distinguish them from a severe hypothyroid state.

Hyponatremia can be a clue pointing toward thyroid storm in this context because the stress of a severe thyrotoxic crisis Often drives non-osmotic ADH release and fluid shifts, leading to dilutional hyponatremia. In contrast, myxedema coma is classically associated with hypothermia, mental status depression, and hemodynamic collapse, with hyponatremia occurring but not as a defining differentiator in the same way. So among the options, hyponatremia is presented as the distinguishing lab feature in this scenario.

As a reminder, fever and tachycardia with a hyperadrenergic state are hallmark features favoring thyroid storm, whereas hypothermia and coma point toward myxedema coma; hypotension can be seen in both, and hypercalcemia is not a typical feature that helps differentiate them.