Greater Proptosis Is Not Associated With Improved Compressive Optic Neuropathy in Thyroid Eye Disease

Imaging of dysthyroid optic neuropathy

Dysthyroid optic neuropathy (DON) is a sight-threatening complication of thyroid eye disease and can lead to permanent vision loss if not treated early. Imaging with computed tomography (CT) or magnetic resonance imaging (MRI) can aid in the diagnosis and early recognition of DON. A number of quantitative and qualitative imaging features have been associated with DON. This article summarises the definition, prevalence, and utility of these radiological findings in the diagnosis of DON.

Diagnostic methods for dysthyroid optic neuropathy: A systematic review and analysis

Diagnosis of dysthyroid optic neuropathy (DON) typically relies on a set of diagnostic clinical features, including decreased visual acuity, impaired color vision, presence of relative afferent pupillary defect, optic disc swelling and ancillary tests including visual field (VF), pattern visual evoked potential (pVEP), and apical crowding or optic nerve stretching on neuroimaging. We summarize various diagnostic methods to establish or rule out DON. A total of 95 studies (involving 4619 DON eyes) met the inclusion criteria. All of the studies considered clinical features as evidence of DON, while most of the studies confirmed DON diagnosis by combining clinical features with ancillary tests. Forty studies (42.1%) used at least 2 out of the 3 tests (VF, pVEP and neuroimaging) and 13 studies (13.7%) used all 3 tests to diagnose DON. In 64 % of the published studies regarding DON, the diagnostic methods of DON were not specified. It is important to note the limitations of relying solely on clinical features for diagnosing DON. On the other hand, since some eyes with optic neuropathy can be normal in one ancillary test, but abnormal in another, using more than one ancillary test to aid diagnosis is crucial and should be interpreted in correlation with clinical features. We found that the diagnostic methods of DON in most studies involved using a combination of specific clinical features and at least 2 ancillary tests.

Increased Orbital Muscle Fraction Diagnosed by Semi-Automatic Volumetry: A Risk Factor for Severe Visual Impairment with Excellent Response to Surgical Decompression in Graves’ Orbitopathy

Graves’ orbitopathy (GO) leads to increased orbital tissue and causes symptoms such as exophthalmos, functional complaints, or dysthyroid optic neuropathy. Different GO types with fat and/or muscle enlargement were identified, and increased muscle appears to particularly influence visual status and treatment response. The current study examines visual parameters dependent on orbital muscle volume fraction in a surgically treated GO cohort. After volumetric analysis of the preoperative orbital content, 83 orbits in 47 patients were categorized into predefined groups (increased or not-increased muscle fraction). All cases underwent pterional orbital decompression, and pre- and postoperative visual status was retrospectively analyzed. Forty-one orbits revealed increased and 42 orbits revealed not-increased muscle volume (mean fraction 29.63% versus (vs.) 15.60%). The preoperative visual acuity (VA) was significantly lower in orbits with increased vs. not-increased muscle volume (mean VA 0.30 vs. 0.53, difference 2.5 lines). After surgery, mean VA improved significantly by 1.7 lines in orbits with increased muscle volume. Not preoperative, but postoperative exophthalmos was significantly lower in orbits with not-increased muscle volume. Increased orbital muscle is associated with significantly reduced VA, but can be remarkably improved by pterional orbital decompression. Therefore, surgical therapy should be considered particularly in decreased VA with orbital muscle enlargement.

Multiparametric quantitative MRI for the evaluation of dysthyroid optic neuropathy

OBJECTIVE

To evaluate the ability of quantitative MRI parameters for predicting dysthyroid optic neuropathy (DON).

METHODS

We retrospectively collected and analyzed the clinical features and 3.0 T MRI data of 59 patients with Graves orbitopathy (GO), with (n = 26) and without DON (n = 33). We compared MRI quantitative parameters, including the modified muscle index (mMI), proptosis, volume of intra-orbital fat, mean apparent diffusion coefficient value, and T2 value of the optic nerve among patients with and without DON. A logistic regression analysis was performed to identify the risk factors associated with DON. Moreover, we performed a receiver operating characteristic curve analysis and decision curve analysis to evaluate the diagnostic performance of the identified parameters for DON.

RESULTS

We studied 118 orbits (43 and 75 with and without DON, respectively). The mMI and mean T2 value of the optic nerve were significantly greater in orbits with DON (p < 0.001). A greater mMI at 21 mm (odds ratio (OR), 1.039; 95% confidence interval (CI): 1.019, 1.058) and higher mean T2 value of the optic nerve (OR, 1.035; 95% CI: 1.017, 1.054) were associated with a higher risk of DON. A model combining the mMI at 21 mm and mean T2 values for the optic nerve effectively predicted DON in patients with GO, with a sensitivity and specificity of 95.3% and 76%, respectively.

CONCLUSION

A quantitative MRI parameter combining the mMI at 21 mm and mean T2 value of the optic nerve can be an effective imaging marker for identifying DON.

KEY POINTS

• Patients with GO and DON had greater mMI than those without DON. • Optic nerves in patients with DON demonstrated an increased T2 value. • The quantitative MRI parameter combining the mMI at 21 mm and mean T2 value of the optic nerve is the most effective method for diagnosing DON.

Pterional Orbit Decompression in Grave Disease with Dysthyroid Optic Neuropathy

OBJECTIVE

The choice of surgical technique in sight-threatening Grave orbitopathy remains controversial. Available data are mostly derived from mixed cohorts with multiple surgical indications and techniques. The authors assessed predictors for visual outcome after standardized pterional orbital decompression for dysthyroid optic neuropathy.

METHODS

Retrospective analysis of 62 pterional orbital decompressions performed on 40 patients with dysthyroid optic neuropathy.

RESULTS

Visual acuity improved by an average of 3.8 lines in eyes with preoperative visual impairment (95% confidence interval [CI]: 1.8-5.8 lines, P < 0.001) and remained stable in eyes without prior visual impairment (95% CI -1.3 to 1 line, P = 0.81). Proptosis was reduced by an average of 3.1 mm (95% CI 1.8-4.3 mm, P < 0.001). Higher degrees of proptosis were predictive of worse visual outcomes (P = 0.017). New-onset diplopia developed in 2 patients, while previous diplopia resolved after surgery in 6 patients.

CONCLUSIONS

This cohort is the largest series of pterional orbit decompressions and the first to focus exclusively on dysthyroid neuropathy. Complication rates were low. Decompression surgery was highly effective at restoring and maintaining visual acuity in patients with dysthyroid optic neuropathy.