This youngster was so weak that he had difficulty moving himself around the stretcher. His EKG actually provides some explanation of his situation:
Sinus rhythm at 72/minute
Axis normal (60°)
PR normal (0.16), QRS normal
QT appears to be prolonged, look especially in III and V3
The ST-segment and T wave changes on this EKG can be explained by hypokalemia. As potassium levels decline U waves appear following the T wave. At the same time T waves will diminish. When severe, the T wave may disappear and a prominent U wave can be mistaken for the T wave, thus one of the reasons that hypokalemia is always included in a differential for prolonged QT interval.
This young man was extremely hypokalemic, with a K+ of 1.7mEq. Pediatric endocrinology came up with an interesting diagnosis – thyrotoxic periodic paralysis! His weakness improved with repletion of his K+ and further treatment of the thyroid disorder.