Hypokalemic Hypophosphatemic Thyrotoxic Periodic Paralysis Associated with Bipolar Disorder Therapy

Hypokalemic thyrotoxic periodic paralysis (TPP) is a rare complication of hyperthyroidism. TPP occurs due to the intracellular shift of potassium in the setting of elevated thyroid hormone. As potassium begins to be replenished, there is a risk of inducing hyperkalemia due to the extracellular shift of potassium. Therefore, it is recommended to replete potassium conservatively. There have been a number of studies reviewing the possible benefits of elevated thyroid hormone in treating bipolar disorder. In this case report, a 37-year-old man with a past medical history of hypothyroidism and bipolar disorder presented with bilateral lower extremity paralysis. Liothyronine was added to his stable hypothyroid regimen for bipolar management. His initial labs on presentation were notable for severe hypokalemia, hypophosphatemia, and an undetectable thyroid-stimulating hormone (TSH). He was diagnosed with TPP, and his electrolytes were corrected with minimal repletion within 24 hours. More research is still required before concluding the role of thyroid hormone in mood disorders. This case report demonstrates a serious complication of supplemental thyroid hormone use. It is crucial to monitor thyroid function tests closely in order to avoid iatrogenic hyperthyroidism.