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

BACKGROUND: 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. METHODS: 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. RESULTS: 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). CONCLUSION: We conclude that MIBI scan is a reliable technique in predicting the response to treatment with i.v. calcitriol in patients with secondary hyperparathyroidism.