A white male patient, 25 years old, who consulted due to muscle weakness in the lower limbs that extended to less progressive form, attended the Emergency Department of the Pasteur Hospital (Monto and Superior, Uruguay).
There were no respiratory, swallowing or urinary alterations.
In the last three months he had had similar nocturnal episodes, preceded by cramps and myalgias, which remitted spontaneously in less than 24 h, whose frequency and intensity increased in the weeks prior to the consultation.
She presented with weight loss, hyperrexia and irritability in the last 6 months, without other symptoms of hyperthyroidism.
His mother was diagnosed with primary hypothyroidism.
The physical examination revealed: anxiety, pale and tender skin, diffuse goiter, tachycardia of 100 cp, systolic hypertension and hypertension of lower limbs, hypoxia and quadriparesis that did not come
Ocular and facial motility were normal, sensitivity was not affected and the rest of the physical examination was normal.
Blood tests revealed hypokalemia of 2.5 mmol/l (3.5-5.0), hypomagnesaemia of 0.56 mmol/l (0.65-1.03), and total hypophosphatemia of 2.3 mg/dl (0.65-0.5).
The thyroid profile indicated primary hyperthyroidism, TSH 0.007 μIU/ml, (0.23-4.20) T4 8.04 ng/dl (0.85-1.70), and T3 > 20 pgr/dl.
Thyroid scintigraphy showed a diffuse goiter, weighing 43 g, approximate hypercapsis, compatible with Graves' disease.
Antithyroid antibodies were not requested.
The diagnosis of thyrotoxic hypokalemic periodic paralysis was formulated and emergency treatment with KCl i.v. rapidly reverting muscle weakness, with rebound hyperkalemia to 24 mmol/K.
Prophylaxis was indicated 40 mg every 8 h and methimazole 10 mg every 8 h, not reiterating symptoms or dysionias.
