Echographic monitoring of response of extraocular muscles to irradiation in Graves' ophthalmopathy

Update on advanced imaging options for thyroid-associated orbitopathy

Thyroid-associated orbitopathy (TAO) is a diverse spectrum of signs and symptoms that appears to have immunologic and pathologic causative factors as diverse as its clinical presentations. Lymphocytes, hormones, and cytokines affect orbital fibroblasts and other similar cells, which exert their effects on orbital tissues, including the extraocular muscles, orbital fat, and optic nerve. This complicated inflammatory cascade and the myriad of clinical findings that result contributes to the active phase of TAO. The distinction between the active and inactive phases of TAO is an important one, as the proper treatment will depend on the disease phase and degree thereof. Several clinical grading scales and scores have been established to help qualify and quantify the disease severity. Aiding clinical exam and acumen, proper and reproducible imaging of the orbit and ocular adnexa is incredibly important to the management of TAO. Orbital ultrasound, computed tomography, magnetic resonance imaging, and scintigraphy each have unique abilities, including quantifying orbital changes, assessing disease activity, correlating orbital findings with clinical changes, guiding appropriate treatment, and monitoring therapeutic responses. Further, study ease, accessibility, cost, sensitivity, specificity, reproducibility, and risks are all important considerations in picking the right test with which to diagnose and follow TAO. This analysis will provide a review of orbital imaging for TAO, including the mechanism of each imaging technique as well as their rationales, advantages, disadvantages, and utilities.

Ultrasonography compared to magnetic resonance imaging in thyroid-associated Graves' ophthalmopathy

OBJECTIVE

To compare ultrasonography (US) to magnetic resonance imaging (MRI) and the clinical activity score (CAS) in Graves' ophthalmopathy.

SUBJECTS AND METHODS

Nineteen patients underwent extraocular muscle thickness measurements by US and MRI, reflectivity by US and signal-intensity ratio by MRI. There were also twelve US control subjects.

RESULTS

US median thicknesses were greater than in controls. Correlation was found between US and MRI in the median thickness of the left eye rectus medial muscle as well as between signal-intensity ratio (SIR) and thickness by US. An inverse correlation was found between reflectivity and SIR in the inferior and lateral rectus. On associating the tests for detecting activity the best results were obtained with CAS plus MRI (sensitivity 75%), and US and MRI (positive predictive value 77% and specificity 80%).

CONCLUSION

CAS and US results showed poor correlation with MRI results suggesting that they cannot replace each other but when combined these methods can improve the evaluation of thyroid-associated ophthalmopathy.

Thyroid eye disease

Thyroid eye disease (TED) is the most common cause of proptosis in adults, and should always be a consideration in patients with unexplained diplopia, pain, or optic nerve dysfunction. At least 80% of TED is associated with Graves disease (GD), and at least 50% of patients with GD develop clinically evident symptomatic TED. The most confusing patients for doctors of all subspecialties are the patients with eye symptoms and signs that precede serum evidence of a thyroid imbalance. Management of TED may include immunosuppressive medications, radiation, or surgery. Although the prognosis for optic nerve function is excellent, the restrictive dysmotility can result in permanent disability. Orbit and eyelid reconstruction are reserved for stable, inactive patients and are the final steps in minimizing facial alterations and enhancing the patient's daily functioning.

Recent developments in Graves' ophthalmopathy imaging

Orbital ultrasound, computed tomography, and magnetic resonance are commonly used as imaging techniques to demonstrate pathological changes in ocular adnexa of patients with Graves' ophthalmopathy. Low cost, short time of investigation, and lack of radiation characterize ultrasound. Nevertheless, a clear differentiation regarding disease activity is not possible, nor is the evaluation of orbital tissue precise enough. Short investigation time, precise imaging of the orbital apex and moderate costs are advantages of tomography. This method delivers a significant radiation dose to the lens, which if repeated constitutes a risk for cataract development. For this reason, magnetic resonance imaging is preferable, particularly if repeated scans are required to assess response to treatment. Precise tissue differentiation and lack of ionizing radiation uniquely suit magnetic resonance for eye studies. Although sensitive in demonstrating interstitial edema within the rectos muscles in active disease, as well as providing a good predictive value with respect to immunosuppressive therapy, quantitative magnetic resonance imaging is an expensive method and is non-specific for the orbital changes in ophthalmopathy. Because of a favorable target to background ratio, octreoscan carries a high sensitivity and may be regarded as a semi-objective tool in the evaluation of patients with Graves' ophthalmopathy, both at initial stages as well as during treatment. A positive orbital octreoscan indicates a clinically active disease in which immunosuppressive treatment might be of therapeutic benefit. However, it is an expensive method with a non-negligible radiation burden. Also, it is neither specific nor does it offer detailed orbital imaging. In summary, in unclear cases of proptosis or recently developed diplopia, prior to orbital decompression surgery, or if imaging is needed in subjects with ophthalmopathy, magnetic resonance actually is the imaging method of choice.

Measuring extraocular muscle volume using dynamic contours

The effect of medical treatment on extraocular muscle enlargement in thyroid associated ophthalmopathy (TAO) may be monitored by measuring the change in volume of the extraocular muscles on serial orbital MRI examinations. In theory, 3D image sets offer the opportunity to minimise errors due to poor repositioning and partial volume effects. This study describes an automated technique for estimating extraocular muscle volumes from 3D datasets. Operator input is minimal and the technique is robust. Verification of the technique on both simulated and real datasets is described. For simulated image sets, both automated segmentation and manual outlining produced estimates of volume which were on average 4% less than "true" volume. For real patient data, extraocular muscle volumes measured by the automated technique were 1.6% (SD 13%) less than volumes measured by manual outlining. Coefficient of variation for repeat outlining of the same image dataset for the automated technique was 1.0%, compared with 4% for manual outlining. The manual technique took an experienced operator approximately 20 min to perform, compared to 7 min for the automated technique. The automated method is therefore rapid, reproducible and at least as accurate as other available methods.

Evaluation of a technique for estimation of extraocular muscle volume using 2D MRI

Measurements of extraocular muscle volume may be useful as an outcome indicator in the assessment of treatment options in thyroid-associated ophthalmopathy. In this study, a technique for estimating extraocular muscle volume from two-dimensional T1 weighted MR images acquired in the coronal plane is described. For each image slice, the cross-sectional area of individual extraocular muscles was estimated using a combination of semi-automated outlining based on a local thresholding technique and manual outlining where thresholding was not possible. The technique was assessed using three sets of images: a computer-generated virtual image set with "extraocular muscles" of known volumes; a set of images from 19 biochemically and clinically euthyroid patients; and images from 7 patients with thyroid-associated ophthalmopathy. From the computer-generated images, the accuracy was determined as 7.6%. Intraobserver agreement was investigated using repeated MRI scans on a single subject and repeat outlining of muscles on five sets of images from different subjects. The mean difference between repeat measurements was 2% (SD 5.9%). We conclude that two-dimensional MR images can be used to determine changes in muscle volume of greater than 12% during treatment of thyroid-associated ophthalmopathy.

Assessment of disease activity in Graves' ophthalmopathy by orbital ultrasonography and clinical parameters

OBJECTIVE

To study if A-mode ultrasonography (US) in combination with the Clinical Activity Score (CAS) and duration of Graves' ophthalmopathy (GO) could predict the response to immunosuppression in Graves' ophthalmopathy.

DESIGN

A prospective clinical study.

PATIENTS AND METHODS

Fifty-six consecutive patients with moderately severe GO were treated with retrobulbar irradiation (10 fractions of 2 Gy). Before treatment the internal reflectivity in the extraocular eye muscles, the CAS, and the duration of Graves' ophthalmopathy were assessed and related to the therapeutic outcome 26 weeks after irradiation.

RESULTS

Twenty-eight (50%) of the patients responded favourably to radiotherapy (four patients became worse, and 24 did not change), and the eye muscle echogenecity indeed tended to be lower in the responders than in the non-responders (P = 0.09). From a receiver operator characteristics curve, a cut-off value of 30% yielded a good positive predictive value of 85%, but the negative predictive value was only 60%. The CAS (>/= 4/10) had a positive predictive value of 65%, and a negative predictive value of 56%. When combining the ultrasound with the CAS, the positive predictive value increased to 74% and the negative predictive value to 72%. Adding the duration of eye symptoms (cut-off 18 months), the prediction of response further improved: positive predictive value 79%, and negative predictive value 89%.

CONCLUSIONS

A-mode ultrasonography has a rather good positive predictive value, but its poor negative predictive value precludes its use as sole activity parameter. By adding the Clinical Activity Score and duration of Graves' ophthalmopathy, the negative predictive value increased considerably. By using this combination, inactive disease can be identified more precise, permitting rehabilitative surgery at an earlier stage in these patients.

Progressive visual loss and ophthalmoplegia

A 51-year-old woman with hyperthyroidism presented with a 4-week history of bilateral progressive visual loss despite treatment with oral prednisone. Her visual function improved after bilateral orbital decompression. The indications for and advantages and disadvantages of radiation therapy and orbital decompression in TAO are discussed. The management of intraocular pressure, strabismus, and lid abnormalities in TAO is also addressed.

[Endocrine orbitopathy: comparison of the long-term result and classification after radiotherapy]

BACKGROUND

This study compares 4 classifications in patients with progressive refractory Graves orbitopathy (GO) and examines their prognostic value in long-term follow-up.

PATIENTS AND METHODS

From 1984 to 1994, 60 consecutive patients (49 female, 11 male) received 20 Gy (10 x 2 Gy) radiotherapy with 6 MV Linac photons. Ocular symptoms and functional impairment was evaluated according to 4 GO-classification systems: Werner-, modified ATA- and Stanford-Score and Ophthalmopathy-Index (OI) according to Grussendorf. In addition, all patients noted their subjective response on a linear scale (0 to 100%).

RESULTS

Improvement was achieved within 1 year after radiotherapy according to the Werner-Score in 28 (47%) patients in > or = 1 symptom category, according to the modified ATA-score in 48 (80%), the Stanford-score in 47 (78%) and the OI-Score in 55 (92%) patients (reduction of > 2 points). The Werner-Score correlated less to the other scores (coefficient r < 0.5) than the other scores among themselves (r approximately 0.9). The ATA-Score improved in the different symptom categories between 47% (stage VI) and 87% (stage V). The OI-Score was reduced by a mean of 6 points. The patients reached a mean subjective improvement of +70 +/- 25%. Acute or chronic side effects were not observed. In multivariate analysis the "male gender" (p = 0.08), a "symptom duration prior to radiotherapy > 1 year" (p = 0.14) and a "high symptom category" (p = 0.11) indicated a negative prognostic trend.

CONCLUSIONS

External radiotherapy is effective for severe, progressive GO after pretreatment. A minimum follow-up of at least 12 months and standardized classification and success criteria are required.

The measurement of change in Graves' ophthalmopathy

Precise measurements of treatment response are a prerequisite for correct interpretation of therapeutic benefit. In the field of Graves' ophthalmopathy we have relied for too long on methods of measurement that are poorly reproducible, subjective, and that often rely on indices derived from aggregated measurements and subjective impressions. In consequence, our conclusions about the benefits of particular therapies are frequently controversial. Until the pathogenic agent of Graves' ophthalmopathy has been identified and is measurable, we are forced to limit our observations to the consequences of the action of that agent. Two critically important consequences are swelling of the retrobulbar muscles and connective tissue and shortening of the extraocular muscle range of contraction. From these primary events all the clinical features of Graves' ophthalmopathy are derived. Effective treatment of Graves' eye disease will affect at least one of five relevant measurements. These are: lid fissure width, range of extraocular motion, diplopia fields, and volume of retrobulbar muscle and connective tissue. These measurements, selected to correspond to the claims of the particular therapy under study, are recommended as the indicators of choice in clinical trials.