Endocrine Abstracts

Background: Graves disease with elevated Immunoglobulin G4 serum concentration is a novel subtype of Graves disease (GD), which seems to be particularly associated with Graves orbitopathy (GO). It occurs in 17.6% of patients with GO and 5.4% of patients with GD without GO. In this study, we compare multiple magnetic resonance imaging (MRI) features of GO with elevated IgG4 serum concentration (IgG4-GO) with the classic GO subtype without IgG4 elevation. No such research has been performed to date.

Methods: We recruited 39 patients with GO. An unenhanced MRI of the orbits was performed on a 3T scanner. T1 weighted (T1WI) and short tau inversion recovery (STIR) sequences were obtained. The dimensions of orbital structures, extraocular muscles (EOM), and the presence of fatty infiltration were assessed on T1WI. The signal intensity (SI) was evaluated on the STIR sequence. Two assessors evaluated all images. IgG4 serum values were measured. Patients with IgG4 values >135 mg/dl were placed in the IgG4-GO group.

Results: There were 11 patients with elevated and 27 with normal IgG4 serum concentration. Patients with IgG4-GO had a larger diameter of the lateral rectus (5.25 [4.73; 5.88] vs 3.98 [3.49; 4.45], P=0.004), medial rectus (7.85 [5.68; 8.58] vs 5.08 [4.15; 5.45], P=0.027), and superior rectus muscle (5.75 [4.4; 6.78] vs 4.03 [3.14; 5.05], P=0.022). There was no significant difference in the diameter of the inferior rectus, inferior oblique, and superior oblique muscle. Patients with IgG4-GO had higher mean EOM to white matter SI ratio (SIR) (2.24±0.39 vs 1.79±0.32, P>0.001) and higher maximal EOM to white matter (3.03 [2.72; 3.34] vs 2.43 [2.24; 2.69], P>0.001). There was a lower prevalence of EOM fatty infiltration in IgG4-GO patients (9.09% vs 57.14%, P=0.011). The IgG4-GO group had a larger diameter of the lacrimal gland in the long axis (19.5±3.1 vs 17.03±3.44, P=0.046) but not short axis (6.25 [5.43; 7.15] vs 5.35 [4.6; 6.4] mm, P=0.089). IgG4-GO patients had a greater horizontal Barret’s Index (51.88 [41.98; 57.55] vs 41.93 [37.04; 47.84]%, P=0.048) but not vertical Barret’s index. No patient in the IgG4-GO group and only one in the normal IgG4 group had infraorbital nerve enlargement. All patients but one in the normal IgG4 group presented tendon sparing.

Conclusions: Graves orbitopathy with elevated serum IgG4 concentration is characterized by larger diameters of several EOMs, higher EOM mean and maximal signal intensity ratio on STIR, larger lacrimal gland size, and a lower prevalence of EOM fatty infiltration.