Clinical significance of metabolic superscan in patients with hyperthyroidism.

Background: Hyperthyroid patients commonly complain of generalized bony aches, which are frequently overlooked due to the more prominent symptoms of cardiovascular and nervous disturbances. Hyperthyroid patients are expected to have abnormal bone metabolism as part of the generalized hypermetabolic status. The aim of this study is to verify the presence of metabolic bone superscan in association with the hypermetabolic stats in various groups of hyperthyroidism. Secondly, to correlate these superscan features with the various laboratory results in hyperthyroid patients.

Material And Methods: Forty-five hyperthyroid patients confirmed by clinical and laboratory results were enrolled in this work. In all patients, a (99m)Tc-pertechnetate thyroid uptake scan was acquired. On a different day, total body bone scan was acquired three hours post IV injection of 555-925 MBq of (99m)Tc-MDP. Serum FT3, FT4, TSH, Ca++, alkaline phosphatase (AP) and parathyroid hormone (PTH) were monitored in all patients as markers of thyroid and bone metabolism. Ten cases with no thyroid diseases were included as a control group. Patients with thyroiditis or long history of antithyroid drugs for more than one year were excluded from the study.

Results: The patients were subdivided into three groups: Graves disease (GD) (n = 30), toxic nodular goiter (TNG) (n = 10) and autonomous toxic adenoma (AT) (n = 5). The TSH for the whole group was significantly suppressed compared to the control group with higher suppression in the Graves disease group than in the TNG or AT groups. (99m)Tc-pertechnetate uptake values in the Graves disease group were significantly higher than the TNG and AT groups (p < 0.05). Metabolic superscan (MSS) was noted in 90% of the Graves cases, 20% in TNG and in none of the AT group. There were no significant differences regarding Ca+, AP and PTH between the Graves and non-Graves groups (p > 0.05).

Conclusions: Disturbances in bone metabolism are more prevalent in Graves disease than in other types of hyperthyroidism. The addition of the bone scan to the diagnostic work up of patients with Graves disease is a sensitive indicator for metabolic bone changes and could help in the future management and follow up for this group of patients.