Long-term intravenous calcitriol in secondary hyperparathyroidism: the role of technetium-99m-MIBI scintigraphy in predicting the response to treatment.

Despite the effectiveness of intravenous calcitriol in suppressing parathyroid hormone secretion in patients with uremic hyperparathyroidism, 50% of the patients remain refractory to this treatment. There are conflicting reports regarding the factors that can predict the response to treatment. Technetium-99m-MIBI scintigraphy was found to be correlated with functional activity of the parathyroid gland. We, retrospectively, evaluated 16 chronic hemodialysis patients, who were maintained on i.v. calcitriol for 36 months or longer, and who had MIBI scan either at the start of, or within the first 6 months of starting calcitriol. Nine patients had a positive uptake (+ve group), and 7 patients had a negative uptake (-ve group). All patients had an elevated iPTH (iPTH > 300 pg/ml) at the start of treatment. The percentage reduction of iPTH in the (-ve) and the (+ve) groups was 65% versus 45% at 12 months, and 65% versus 10% at 36 months respectively. In long-term follow-up of 36 months, all the patients in the (-ve) group responded to calcitriol; while 8 of the 9 patients (89%) in the (+ve) group didn't respond. The difference in response between the 2 groups was statistically significant (p<0.001). We conclude that MIBI scan is a reliable technique in predicting the response to treatment with i.v. calcitriol in patients with secondary hyperparathyroidism.