Effect of calcium channel blockers on the sensitivity of preoperative 99MTC-MIBI SPECT for hyperparathyroidism

Background. 7 Technetium 99m (Tc-99m)-methoxyisobutylisonitrile (MIBI) single photon emission computed tomography (SPECT) is frequently used in the evaluation of patients with hyperparathyroidism. Calcium channel blockers (CACBs) may affect Tc-99m-MIBI uptake by parathyroid cells. This study examines the effect of CACB therapy on the sensitivity of Tc-99m-MIBI SPECT localization for hyperparathyroidism. Methods. Two hundred fifty-three operated patients with hyperparathyroidism were retrospectively reviewed. The potential effect of CA CB therapy on Tc-99m MIBI scan sensitivity was examined by using logistic regression analysis. Possible confounding factors were considered. Results. Among 235 patients, those with multiple endocrine neoplasia, type I (MEN-I), MEN-IIA, 4-gland hyperplasia, secondary hyperparathyroidism, and tertiary hyperparathyroidism exhibited no difference associated with CA CB use. Of the remaining 198 patients with primary hyperparathyroidism, 7130 (23%) with negative Tc-99m-MIBI SPE,CTscans compared to 241168 (14 %) with positive scans used CA CBs. After correcting for age, gender and gland weight, the odds ratio (OR) for a negative study in patients taking CA CBs was 2.88 (95 % CI, 1.03-8.10; P =.045). Atherosclerosis, hypertension, diabetes mellitus, preoperative calcium and parathyroid hormone levels, and thyroid hormone use were not confounding factors. Conclusions. CACB therapy reduces the sensitivity of Te-99m-MIBI parathyroid SPECT in patients with primary hyperparathyroidism. Further studies are required to determine the potential reversibility of this effect with termination of CACB therapy.