A 30-year-old woman presented with a progressive neurologic disorder characterized by seizures, buccolingual dyskinesias, orofacial tics, choreiform movements, atrophy, and areflexia. Investigations revealed normal lipid profile except for aprebetalipoproteinemia. Phase-contrast and electron microscopy showed 35 to 40% acanthocytes. MRI and 18fluorodeoxyglucose-PET studies showed caudate atrophy and hypometabolism. The phenotype of this patient is neuroacanthocytosis and its association with aprebetalipoproteinemia may represent a new subentity of the disorder.
The protein binding of disopyramide is altered when concentration is increased within the therapeutic range. A wide range of free concentrations may be produced at a given total concentration. The present study assessed whether intracardiac electrophysiologic responses to disopyramide related better to free or to total concentration. Intravenous infusions of disopyramide were evaluated in 17 patients with inducible sustained ventricular tachycardia. The first maintenance infusion produced total serum concentrations of 11.7 +/- 2 mumols/L, and no significant increase occurred at higher-dose infusions. However, free concentrations during the first and second maintenance infusions were significantly different at 5.3 +/- 1 mumols/L and 6.8 +/- 1 mumols/L, respectively. Free fraction also increased significantly, from 45% +/- 8% to 50% +/- 7%. Overall change in QTc interval and ventricular tachycardia cycle length correlated with free concentration but not with total concentration. This study showed that some intracardiac measurements correlate with free concentration but that none correlate with total concentration.
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