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Dear editor, Hypokalemic periodic paralysis (HPP), is a rare neuromuscular disorder caused by dysfunction of the ion channels in red muscle cells which is characterized by painless episodes of muscle weakness generally after strenuous exertion or a high-carbohydrate meal. Most of HPP cases are hereditary because the disease is autosomal dominant inherited. However, some HPP patients secondary to thyrotoxicosis are also described. Thyrotoxic hypokalemic periodic paralysis (THPP), unlike the other thyroid diseases, is predominantly seen in men.  Here we report a case presenting with paralysis with no known chronic illness and then diagnosed as thyrotoxicosis and hypokalemic periodic paralysis caused by this thyroid disease. A 41-year- old Caucasian man, without any chronic disease, presented to our emergency department with generalized muscle weakness pronounced in his both upper and lower extremities. He recalled many similar but milder episodes in the previous 2 months. The physical examination made by a neurologist had no pathology but only quadriparesis (bilateral upper extremities 3/5, bilateral lower extremities 4/5). His initial potassium level was 1.5 mEq/L on admission and his electrocardiogram showed an obvious U wave (Figure1). An initial diagnosis of hypokalemic periodic paralysis was made and he was immediately given intravenous potassium chloride in the emergency department. Then he was interned and after getting a detailed anamnesis, it was learned that he had no family history like his and he had a high-carbohydrate diet a few hours before the quadriparesis occurred. On admission, blood pressure was 140/80 mmHg and heart-rate 90 beats/minute. Physical examination revealed a slightly enlarged thyroid gland without nodules and exophthalmos was present. The findings of other systems were normal. Thyroid stimulating hormone (TSH) level was u003c0.03 μU/mL (0.25–5.0), free thyroxine level (fT4) 4.21 ng/dL (0.77–1.71), and free tri-iodothyronine (fT3) 19.55 ng/dL (0.23–0.39), anti-thyroid peroxidase antibodies (Anti-TPO) 2261 IU/mL (l9.0 IU/mL). Thyroid ultrasound showed us the left lobe measured 27x28x29mm, the right lobe measured 35x31x30mm. The gland appeared enlarged and heterogeneous in texture. The internal septations were observed. Thyroid scintigraphy led us to diagnose Graves’ disease. Under these findings, the patient was diagnosed as having THPP associated with Graves’ thyrotoxicosis and treatment with methimazole was initiated. Serial measurements of his serum potassium level which was too low on admission and then became normal after administering intravenous potassium chloride, remained within normal limits without any oral potassium supplements in the hospital. Treatment with propranolol was also initiated as 4x40mg per day and the patient was discharged home with the diagnosis of THPP secondary to Gravesu0027 disease. THPP is a sporadic form of HPP and it occurs in association with hyperthyroidism. In most cases of THPP, the main underlying cause is Graves’ disease. More than 95 percent of THPP cases are seen in men, despite the tendency of women to have thyroid illnesses. The pathogenesis of THPP, which is a rare complication of thyrotoxicosis causing hypokalemia only during episodes, is the activation of Na + /K + -ATPase pump because of hyperinsulinemia, increasing of thyroid hormones, catecholamines and beta-adrenergic stimulation. Besides all those factors, resting after exercise can also increase Na + /K + -ATPase activity in skeletal muscle and promotes influx of potassium. 3, 4 Therefore, B receptor blockage, anti-thyroid drugs and avoiding precipitating factors such as high-carbohydrate meals are recommended for treatment and prophylaxis of THPP, instead of administering potassium only. Unless there are cardiopulmonary complications, KCl infusion should be given at a slow rate, because it may result in rebound hyperkalemia as potassium shifts back into the intravascular compartment.  In this case report, we wanted to share our patient with THPP who was not aware of his thyroid disease like most of the patients described in the literature. Our aim by presenting this case is to emphasize the importance of a good anamnesis and physical examination leading to a right diagnosis and treatment.

Thyrotoxic hypokalemic periodic paralysis in a Turkish patient presenting with a U wave on ECG