Clinical manifestations of thyrotoxic periodic paralysis
General
Male predominance; initiation at age 20 to 40
Periodic flaccid paralysis of proximal muscles, mainly of lower extremities
Negative family history of similar symptoms
Hypertension
Subtle clinical features of hyperthyroidism
Laboratory findings
Hypokalemia, hypophosphatemia, and mild hypomagnesemia
Normal acid-base balance
Low potassium excretion rate (low urinary potassium- creatinine ratio and low TTKG)
Hypercalciuria and hypophosphaturia
Abnormal thyroid function tests (low TSH; elevated free and total T4 and T3; increased T3 uptake)
Electrocardiographic abnormalities
Sinus tachycardia
Hypokalemic changes: prominent U wave, prolonged PR interval, increased
P-wave amplitude, widened QRS complexes
First-degree atrioventricular block
Atrial and ventricular arrhythmias
Electromyography: low-amplitude compound muscle action potential with no change after epinephrine.
TTKG indicates transtubular potassium gradient (a semiquantitative index of the activity of the potassium secretory process calculated as [urine K/(urine osmolality/plasma osmolality)]/plasma K); TSH: thyroid-stimulating hormone; T4: serum thyroxine; T3: triiodothyronine.
