The application of extraocular muscle maximum standardized uptake value of 99mTc-diethylenetriamine pentaacetic acid orbital single photon emission computed tomography/computed tomography in the assessment of Graves' orbitopathy.

Purpose: To study the feasibility and value of assessing patients with Graves' orbitopathy (GO) in 99mTc-diethylenetriamine pentaacetic acid (DTPA) orbital single photon emission computed tomography/computed tomography (SPECT/CT) with extraocular muscle maximum standardized uptake value (SUVmax).

Methods: A total of 235 patients underwent 99mTc-DTPA orbital SPECT/CT, including 176 patients with GO and 59 patients with Graves' disease (GD) as controls. The SUVmax of extraocular muscles, including right medial rectus muscle (RMR), right lateral rectus muscle (RLR), left medial rectus muscle (LMR), left lateral rectus muscle (LLR), was compared between groups, correlation analyses with clinical activity scores (CAS) and serological indices was performed, and the diagnostic efficacy was evaluated using receiver operating characteristic curves. The consistency of SPECT/CT and MRI in assessing extraocular muscle activity was compared.

Results: SUVmax in the extraocular muscles of active GO patients was significantly higher than in inactive GO patients and controls. In GO patients, SUVmax of the medial rectus (LMR most prominent) was higher than that of the lateral rectus. SUVmax correlated with CAS, thyroid-stimulating hormone, total cholesterol, low-density lipoprotein (positively) and free triiodothyronine and free thyroxine (negatively), but not with GO duration. The optimal cutoff values for distinguishing between active and inactive SUVmax were identified. RLR had high sensitivity and RMR had high specificity. SPECT/CT and MRI showed moderate agreement in assessing extraocular muscle activity in 87 GO patients, with high concordance.

Conclusions: The extraocular muscle SUVmax of 99mTc-DTPA orbital SPECT/CT may be used as an adjunct method in combination with CAS to more accurately assess GO activity, which can help in clinical diagnosis and individualized treatment.