Working Diagnosis:
Thyrotoxic Periodic Paralysis- A rare electrolyte abnormality precipitated by a hyperthyroid state, most commonly Graves disease or toxic nodular goiter. Weakness and/or paralysis may result from an intracellular shift of potassium leading to hypokalemia. This is commonly triggered by exercise. Exercise-induced increases in sodium-potassium ATPase pump activity and insulin responsiveness are postulated to contribute to the hypokalemia seen in these cases.

Treatment:
Patient received parenteral fluids and potassium while in the emergency department, with resultant improvement of his symptoms. Once complete resolution of the patient symptoms was achieved, further potassium supplementation was held as thyrotoxic periodic paralysis results from an intrinsic shift of potassium rather than total body depletion. Patient was monitored overnight in the hospital and discharged the following day with an endocrinology consultation as follow-up. He was instructed to refrain from physical activity until adequate control of his thyroid function is achieved.

Outcome:
The patient is currently undergoing workup to establish the cause of his thyroid dysfunction. The evaluation will include a thyroid ultrasound and a radioactive iodine uptake scan. A full recovery is expected once a euthyroid state is achieved.

Author's Comments:
This case highlights the importance of a thorough physical exam, specifically the neurological exam, which helps to establish the appropriate differential diagnosis. In addition, it is important to consider other diagnoses on the differential of dehydration when a patient or athlete presents with profound neurologic symptoms or recurrent bouts of dehydration-like symptoms.

Editor's Comments:
Though most of us will never see a case like this, this case is a good reminder that thyroid studies need to be added to the laboratory workup for weakness and hypokalemia.

Athletes with hyperthyroidism should be questioned repeatedly about supplement use. Internet available "energy" supplements may contain dessicated animal thyroid but not have this listed on their label. Before thyroid ablative treatment is pursued, a thorough review of supplements is strongly recommended.

References:
1.Manoukian MA, Foote JA, Crapo LM. Clinical and metabolic features of thyrotoxic periodic paralysis in 24 episodes. Archives of Internal Medicine. 1999;159(6):60-606.
2.Lin S-H, Lin Y-F, Halperin ML. Hypokalaemia and paralysis. QJM. 2001;94(3):133-139.
3.Ober KP. Thyrotoxic periodic paralysis in the United States. Report of 7 cases and review of the literature. Medicine. 1992;71(3):109-120.

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