Preliminary Diffusion-Tensor Imaging Evidence for Trans-Synaptic Axonal Degeneration in Dysthyroid Optic Neuropathy Due to Thyroid-Associated Ophthalmopathy.

BACKGROUND: The mechanism driving dysthyroid optic neuropathy (DON) is unclear. Diffusion-tensor imaging (DTI) allows for noninvasively assessing the microstructure of the entire visual pathway and may facilitate a better understanding of the mechanism of DON. PURPOSE: To assess microstructural changes of the whole visual pathway and to investigate the potential mechanism of trans-synaptic damage（TSD） pathogenesis in DON with DTI. STUDY TYPE: Cross-sectional. POPULATION: Sixty-four patients with bilateral thyroid-associated ophthalmopathy (TAO), 30 with and 34 without DON, and 30 age- and sex-matched healthy controls (HCs). FIELD STRENGTH/SEQUENCE: 3 T/DTI (A single-shot diffusion-weighted echo-planar imaging sequence). ASSESSMENT: Differences in DTI parameters including fractional anisotropy (FA), mean diffusivity (MD), axial diffusivity (AD), and radial diffusivity (RD) in each segment (optic nerve, tract, and radiation) of the entire visual pathway among the groups were compared. The parameters of visual evoked potentials (VEPs), visual field tests, and mean retinal nerve fiber layer (mRNFL) thickness on optical coherence tomography were also compared across patients. STATISTICAL TESTS: Student's t-test, chi-square test; ANOVA with post-hoc testing, interclass correlation coefficient, and correlation analysis. Significance level: P < 0.05. RESULTS: TAO patients with DON showed significantly reduced mRNFL thickness and abnormal VEPs. There was a tendency for gradually reduced FA and AD, and increased RD and MD from HCs, with non-DON to with DON in optic nerve and tract, statistically. For radiation, the RD and MD showed statistical increase, the AD and FA just showed numerical decrease (P = 0.119 and 0.059, respectively). For DON, the FA and MD of visual pathway segments showed correlations with abnormal VEPs. DATA CONCLUSION: DTI may be a useful tool for detecting microstructural changes in the entire visual pathway in DON. The changes in RNFL thickness and DTI parameters suggested TSD as a potential pathogenic mechanism of DON. EVIDENCE LEVEL: 4 Technical Efficacy: Stage 5.

Multi-Parametric Diffusion Tensor Imaging of The Optic Nerve for Detection of Dysthyroid Optic Neuropathy in Patients With Thyroid-Associated Ophthalmopathy.

Objective: To evaluate the microstructural changes of the orbital optic nerve in thyroid-associated ophthalmopathy (TAO) patients with or without dysthyroid optic neuropathy (DON) using diffusion tensor imaging (DTI) and investigate whether DTI can be used to detect DON. Materials and Methods: 59 bilateral TAO patients with (n= 23) and without DON (non-DON, n= 36) who underwent pretreatment DTI were included and 118 orbits were analyzed. The clinical features of all patients were collected. DTI parameters, including mean, axial, and radial diffusivity (MD, AD, and RD, respectively) and fractional anisotropy (FA) of the intra-orbital optic nerve for each orbit were calculated and compared between the DON and non-DON groups. ROC curves were generated to evaluate the diagnostic performance of single or combined DTI parameters. Correlations between DTI parameters and ophthalmological characteristics were analyzed using correlation analysis. Results: Compared with non-DON, the DON group showed decreased FA and increased MD, RD, and AD (P < 0.01). In the differentiation of DON from non-DON, the MD was optimal individually, and the combination of the four parameters had the best diagnostic performance. There were significant correlations between the optic nerve's four DTI metrics and the visual acuity and clinical active score (P < 0.05). In addition, optic nerve FA was significantly associated with the amplitude of visual evoked potentials (P = 0.022). Conclusions: DTI is a promising technique in assessing microstructural changes of optic nerve in patients with DON, and it facilitates differentiation of DON from non-DON eyes in patients with TAO.