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Asymmetric thyroid eye disease (TED) is reasonably common and TED should be considered in the differential workup of asymmetric orbital inflammatory disease, recent research suggests.¹

鈥淎symmetric presentation of TED may pose diagnostic challenges; thus it is important to be aware of its clinical, biochemical and radiological associations,鈥� first author Khizar Rana, PhD, MBBS, Department of Ophthalmology and Visual Sciences, University of Adelaide, North Terrace, Adelaide, Australia, South Australian Institute of Ophthalmology, Royal Adelaide Hospital, Port Road, Adelaide, Australia, and colleagues noted in International Ophthalmology. 鈥淭he purpose of our study is to evaluate the prevalence of asymmetric TED in an Australian cohort, and determine its clinical, biochemical, and radiological associations. This may help contribute to the broader understanding of asymmetric TED.鈥� 

The report was published in International Ophthalmology.¹

Study design and population

The cohort included 172 orbits from 86 patients who were diagnosed with TED and underwent Hertel exophthalmometry and orbital computed tomography scans. Mean patient age was 54 years and 57 were female. 

TED was diagnosed by neuro-ophthalmologists or orbital surgeons. Asymmetry was defined as a globe protrusion difference 鈮� 3 mm, based on Hertel exophthalmometry performed by neuro-ophthalmologists or orbital surgeons.

Characteristics of patients with asymmetric TED

Overall, asymmetric TED was diagnosed in 28 (33%) patients. There were no significant differences between the asymmetric and symmetric group in gender (65% vs 67% female; P = 0.07) or average age (54.7 vs 53.7 years; P = 0.79). Furthermore, there were no significant differences between the groups in disease activity status (active TED in 11/28 vs 48/144; P = 0.37), dysthyroid optic neuropathy (5/28 vs 15/144; P = 0.26), thyroid hormone status (P = 0.16), anti-thyroid peroxidase (anti-TPO) levels (P = 0.38), or thyroid-stimulating hormone receptor antibody (TSHrAb) levels (P = 0.14). 

Compared with the contralateral orbit, extraocular muscles volumes in the asymmetric orbit were significantly higher for the sum of all muscles (6368 vs 4674 mm³; P < 0.01) and the superior muscle group (1868 vs 1391 mm³; P < 0.01), superior oblique (415 vs 320 mm³; P = 0.02), medial rectus (1275 vs 888 mm3; P < 0.01), lateral rectus (950 vs 749 mm³; P < 0.01), and inferior rectus muscles (1355 vs 890 mm³; P < 0.01). No significant difference in muscle volume was found for the inferior oblique in the asymmetric orbit compared with the contralateral orbit (503 vs 436 mm³; P = 0.15). 

Among patients without asymmetric disease, no significant differences were found in individual muscle volumes in the right and left orbits.

鈥淥ur study found the asymmetric orbit to have significantly higher muscles volumes compared to its contralateral orbit, thus muscle expansion is one of the likely contributing factors to the development of asymmetric proptosis,鈥� the authors wrote.

Conclusions

Their results, the authors said, demonstrated that asymmetric TED is reasonably common in the course of the disease, with no differences in age or gender between patients with asymmetric and symmetric TED. 

鈥淎lthough TED is typically bilateral and symmetric, TED should be considered in the work up of asymmetric orbital inflammatory disease,鈥� noted the researchers. 

The authors also said that, although other studies have noted differences in the thyroid status between patients with and without asymmetric disease, there was no significant corelation between asymmetric disease and thyroid status, anti-TPO levels, or TSHrAb levels, which may have been a result of type 2 error. 

According to the researchers, lack of a standardized definition of asymmetric disease is a main challenge when investigating radiological and clinical associations. They believe that use of a definition based on more objective markers, such as radiologically derived muscles volumes or proptosis, may contribute to standardization and facilitate comparisons among studies. 

Limitations of this study include the retrospective design, which did not allow the authors to investigate inter-rater reliability of measurements from Hertel exophthalmometry. 

鈥淎symmetric TED is reasonably common and may be seen in one-third of TED patients,鈥� the researchers concluded. 鈥淭he extraocular muscles volumes are higher in the asymmetric orbit compared to its contralateral orbit, suggesting muscle volume expansion to be an underlying contributor to asymmetry. In future, use of more objective parameters to define asymmetric TED is required to enable reliable comparisons between studies.鈥�

Published: July 30, 2024