Endocrine Abstracts

Introduction: Thyrotoxic periodic paralysis (TPP) is characterized by muscle paralysis, hypokalemia and thyrotoxicosis. Mutations occurring in the genes that encode for ion channels (CACNA1S and KCNJ18) are thought to be involved in its onset. TPP mainly affects male subjects (M:F=26:1), Asian (2% of Asian subjects with thyrotoxic suffer from TTP), while it is rare in Caucasian population (0.1-0.2% of thyrotoxic subjects). Signs and symptoms of thyrotoxicosis are often absent in TPP patients.

Case Report: In February 2023 a 20-year-old Caucasian patient come to our attention because of weakness of the lower limbs and postural instability that had ensued after intense physical activity. He reported that a similar yet milder episode had occurred a few months earlier. The previous event had resolved spontaneously. The patient complained also of fine distal tremors in the previous six months. At physical examination, we observed weakness and hyporeflexia in the lower limbs. Blood tests showed hypokalemia (1.9 mEq/l), ECG sinus tachycardia (105 bpm) and U waves. Neurological symptoms remitted after intravenous infusion of potassium. At laboratory workup, autoimmune hyperthyroidism was diagnosed: fT4 3.62 ng/dL, (nv 0.7-1.7) fT3 14.9 ng/l (nv 2.7-5.7), TSH 0.014 mIU/l (nv 0.4-4), TRAb 5.02 IU/l (nv <1.5). Neck ultrasound showed a diffuse goiter. Treatment with methimazole was started, with restoration of euthyroidism. The patient did not experience further episodes of paralysis thereafter.

Conclusions: If not recognized and treated, TPP can induce respiratory paralysis and potentially fatal cardiac arrhythmias. It is advisable to evaluate thyroid function in case of non-familial hypokalemic paralysis in male subjects, especially if Asian, even in absence of symptoms suggestive of thyrotoxicosis.