Thyroid-associated ophthalmopathy: linear regression analysis of single photon emission computed tomography

Background: At present, there is still no significant progress in the diagnosis and treatment of thyroidassociated ophthalmopathy.

Objective: We explored the role of ^99mTc-octreotide single photon emission computed tomography (SPECT) in determination of the clinical activity of thyroid-associated ophthalmopathy (TAO).

Methods:A prospective study including 36 cases of TAO and 8 controls was conducted by intravenous injection of ^99mTc-octreotide, followed by SPECT. The radioactive counting ratio was calculated for the orbital/occipital regions of interest (ROI), and the Spearman rank correlation between the average ratio and the corresponding clinical activity score (CAS) mean of ADHOC (Recommendation of the Ad Hoc Committee of The American Thyroid Association in 1992) was analyzed. A curve regression equation for the CAS to orbital/occipital radio counting ratio was determined to calculate the cutoff for TAO activity.

Results: The Spearman rank correlation between orbital/occipital uptake ratio and CAS was calculated (coefficient r = 0.972, p < 0.01). The curve regression equation for all patients with TAO (including the active group and resting group) was (Y) = -66.25 + 106.06 X-52.86 X² + 8.94 X³. The transformational equation of the cubical CAS of exophthalmos (dependent variable Y) to the square root of the orbital/occipital uptake ratio (independent variable X) was (Y) = -752.67 + 676.74 (X). A cutoff of 1.48 was used to identify the active phase of exophthalmos. The sensitivity was 96.0% with a standard error of 3.92%, and the specificity was 94.73 with a standard error of 5.13%.

Conclusion: ^99mTc-octreotide SPECT can objectively and accurately measure TAO activity. An orbital/occipital uptake ratio ≥1.48 is the recommended cutoff to determine the active phase of TAO. This may guide clinical treatment of TAO.