Etidronate therapy decreases the sensitivity of bone scanning with methylene diphosphonate labelled with technetium-99m.

OBJECTIVE: To define the nature, incidence and consequence of a possible interaction between etidronate (for the treatment of hypercalcemia) and methylene diphosphonate labelled with technetium-99m (99mTc-MDP) (for bone scanning).

MATERIALS AND METHODS: The authors reviewed hospital pharmacy records for a period of 2 years and identified 18 patients who had received etidronate. Of this group, 6 patients (4 men and 2 women, ranging in age from 56 to 76 years) had undergone bone scanning with 99mTc-MDP while receiving etidronate. Five of the patients had hypercalcemia associated with metastatic disease, and the sixth had hyperparathyroidism.

RESULTS: All bone scans demonstrated poor uptake of tracer by bone accompanied by high soft-tissue background. There was loss of bone definition below the mid-thigh, and in 5 of the 6 patients there was indistinguishable rib uptake. In 1 of the patients, there was absence of uptake in 2 previously defined metastatic lesions.

CONCLUSION: Recent oral or intravenous administration of etidronate is a contraindication to bone scintigraphy, as it markedly decreases sensitivity for bone disease. Bone scintigraphy should be timed so that it is performed before etidronate treatment or, if that is not possible, more than 2 to 4 weeks after the therapy has been completed.