Imaging of disease activity in Graves' orbitopathy with different methods: comparison of (99m)Tc-DTPA and (99m)Tc-depreotide single photon emission tomography, magnetic resonance imaging and clinical activity scores.

Background: The immunosuppressive treatment of Graves' orbitopathy (GO) influences the course of the disease in the early, active, retrobulbar inflammatory phase (active GO), which cannot be detected by direct clinical examination.

Aim: To evaluate the clinical effectiveness of a newly developed method for the detection of intraorbital inflammatory activity in patients suffering from Graves' orbitopathy, utilizing a four-headed single photon emission tomograph (SPET) camera and (99m)Tc-diethylenetriamine pentaacetic acid (Tc-DTPA).

Methods: The magnetic resonance imaging (MRI) T2 relaxation time score, as a measure of ongoing orbital inflammation (reference method), was compared with the uptake activities (UA) of (99m)Tc-DTPA orbital SPET and the more specific (99m)Tc-Neospect ((99m)Tc-depreotide) SPET, as well as the clinical activity scores (CAS), in 21 patients (42 orbits).

Results: By visual inspection, the 'eye SPET' frames of patients suffering from active GO could be easily distinguished from those with inactive GO. Although the distributions of the two radiopharmaceuticals were mildly different, the information obtained was essentially the same. The MRI activity scores correlated well with both (99m)Tc-DTPA and Tc-depreotide UA. The mean (99m)Tc-DTPA UA value of 25 inactive GO orbits was (6.55 +/- 1.4) x 10(-6) ID x cm3 (where ID is the injected dose); the values of the active GO orbits (12 orbits with an MRI score of 1 and five orbits with an MRI score of 2) were significantly higher: (8.87 +/- 1.63) x 10(-6) and (10.36 +/- 1.60) x 10(-6) ID x cm3, respectively. Similar differences were observed for the (99m)Tc-depreotide UA values: the averages in the inactive and active groups with MRI scores of 1 and 2 were (5.23 +/- 1.23) x 10(-6), (7.69+/-2.24) x 10 and (10.92 +/- 3.85) x 10(-6) ID x cm3, respectively. The (99m)Tc-DTPA accumulation pattern in the orbital region of active GO patients was similar to that of the more specific (99m)Tc-depreotide. There was a good correlation (r = 0.71, P<0.001) between the UA values of the two radiopharmaceuticals, but CAS did not correlate with either of the UA values.

Conclusions: (99m)Tc-DTPA eye SPET is a potentially useful method, allowing rapid imaging at an acceptable cost. It provides essential supplementary information to traditional CAS in assessing disease activity in Graves' orbitopathy.