Conclusion:
In many cases, hypokalemia can be multifactorial. When potassium replacements exceed the calculated deficit values by wide margin and with suboptimal correction of potassium, secondary causes should be entertained.
Persistent, refractory hypokalemia associated with muscle weakness should prompt suspicion for thyrotoxic periodic paralysis. In suspected cases, appropriate testing should include the measurement of free T3 levels along with a free thyroxine and TSH so that T3 toxicosis is not missed.
References:
  1. Lam L, Nair RJ, Tingle L. Thyrotoxic periodic paralysis. Proc (Bayl Univ Med Cent). 2006;19(2):126-129. doi:10.1080/08998280.2006.11928143
  2. Kelley DE, Gharib H, Kennedy FP, Duda RJ Jr, McManis PG. Thyrotoxic periodic paralysis. Report of 10 cases and review of electromyographic findings. Arch Intern Med. 1989 Nov;149(11):2597-600. doi: 10.1001/archinte.149.11.2597. PMID: 2818118
  3. Rhee EP, Scott JA, Dighe AS. Case records of the Massachusetts General Hospital. Case 4-2012. A 37-year-old man with muscle pain, weakness, and weight loss. N Engl J Med. 2012;366(6):553-560. doi:10.1056/NEJMcpc1110051
  4. Lin SH, Huang CL. Mechanism of thyrotoxic periodic paralysis. J Am Soc Nephrol. 2012;23(6):985-988. doi:10.1681/ASN.2012010046
  5. Clausen T. Hormonal and pharmacological modification of plasma potassium homeostasis. Fundam Clin Pharmacol. 2010 Oct;24(5):595-605. doi: 10.1111/j.1472-8206.2010.00859.x. PMID: 20618871.
  6. Clifford PS, Hellsten Y. Vasodilatory mechanisms in contracting skeletal muscle. J Appl Physiol (1985). 2004 Jul;97(1):393-403. doi: 10.1152/japplphysiol.00179.2004. PMID: 15220322.
  7. Abdi H, Amouzegar A, Azizi F. Antithyroid Drugs. Iran J Pharm Res. 2019;18(Suppl1):1-12. doi:10.22037/ijpr.2020.112892.14005
Table 1: Sequential laboratory data