Background: Hypokalemic periodic paralysis (HPP) related to thyrotoxicosis, though rare, is more often seen in Asian males. Type 1 renal tubular acidosis (T1 RTA), which can also cause HPP, is typically managed with alkali therapy and potassium supplementation, though there are no well-established guidelines for management in pregnancy.
Clinical Case: A 27-year-old Puerto Rican woman, at 32 weeks gestation, presented to the hospital with sudden onset muscle weakness, and was found to have 1/5 muscle strength in her lower extremities. She had no personal or family history of similar illness. Laboratory analysis revealed hypokalemia (potassium 2.0 mmol/L, range: 3.5 – 5); non-gap metabolic acidosis (sodium 137mmol/L, range 136 – 145; chloride 113 mmol/L, range 98- 107; and bicarbonate 8 mmol/L, range 22 – 29); and an arterial pH of 7.09. Urine studies demonstrated a urine pH of 6.5 and a urine sodium of 32 mmol/L which was diagnostic of T1 RTA in the context of her metabolic derangements. She was treated emergently with potassium and bicarbonate infusions, with improvement in her symptoms. Subsequent thyroid function testing revealed: a low TSH of 0.01 uIU/ml, normal free T4 of 1.66 (range: 0.9 - 1.7) ng/dl, normal free of T3 3.7 (range: 2.0 -4.4) pg/ml and elevated total T4 of 16.5 (range: 4.5 - 11.7) ug/dl. Renal ultrasound demonstrated medullary nephrocalcinosis. She was discharged on potassium and sodium citrate tablets. At 37 weeks, the patient was readmitted for induction of labor due to pre-eclampsia, and delivered a healthy male baby. Several months later, she presented to the Endocrinology clinic with symptoms of increased frequency bowel movements, palpitations and heat intolerance, which had been ongoing since pregnancy. On review, a metabolic panel prior to pregnancy had demonstrated non-gap acidosis and mild hypokalemia. Further testing demonstrated the following: TSH < 0.01 uIU/ml, Free T4 1.71 ng/dl, Free T3 4.8 pg/ml, TSI 280%, and a thyroid uptake scan with homogenous radiotracer uptake, with a 24-hour uptake of 40%. She was started on methimazole therapy, and continued on potassium and sodium citrate tablets with clinical and biochemical improvement.
Conclusion: Thyrotoxicosis can augment hypokalemia in T1 RTA, and can increase the risk of HPP. Our patient had biochemical evidence of RTA prior to pregnancy, though without episodes of HPP, and we believe that her hyperthyroidism, triggered by pregnancy, may have been the additional insult that precipitated her paralysis. This is the first reported case of HPP related to co-existing thyrotoxicosis and T1 RTA in a pregnant individual.
Reference:1. Tu ML, Fang YW, Leu JG, Tsai MH. An atypical presentation of high potassium renal secretion rate in a patient with thyrotoxic periodic paralysis: a case report. BMC Nephrol. 2018;19(1):160. Published 2018 Jul 4. doi:10.1186/s12882-018-0971-9