Thyroid-Associated Inferior Oblique Myopathy

Abstract

Extraocular muscle involvement may be a sign of thyroid-associated ophthalmopathy (TAO).1Dickinson A.J. Perros P. Controversies in the clinical evaluation of active thyroid-associated orbitopathy: use of a detailed protocol with comparative photographs for objective assessment.Clin Endocrinol. 2001; 55: 283-303Crossref PubMed Scopus (124) Google Scholar The most typical involvement in TAO is of an inferior rectus muscle, whereas the frequency of other muscle involvement is in the order of medial rectus, superior rectus, and lateral rectus.1Dickinson A.J. Perros P. Controversies in the clinical evaluation of active thyroid-associated orbitopathy: use of a detailed protocol with comparative photographs for objective assessment.Clin Endocrinol. 2001; 55: 283-303Crossref PubMed Scopus (124) Google Scholar Superior oblique muscle involvement in TAO is rare but reported.2Thacker N.M. Velez F.G. Demer J.L. Rosenbaum A.L. Superior oblique muscle involvement in thyroid ophthalmopathy.J AAPOS. 2005; 9: 174-178Abstract Full Text Full Text PDF PubMed Scopus (25) Google Scholar However, to the best of our knowledge an inferior oblique muscle lesion in TAO has not been reported. Here, we report a patient with TAO with inferior oblique muscle involvement. Informed consent for this study was obtained from the patient. Magnetic resonance imaging was conducted with a 1.5-tesla system (GE Signa, GE Medical Systems, Waukeshaw, WI) using a custom-designed 5-inch surface coil. We obtained sagittal T2-weighted spin echo sequences (echo time, 80 milliseconds; repetition time, 2500 milliseconds) sliced parallel to the optic nerve. Coronal T2-weighted spin echo sequences were taken under the same conditions. Coronal T1-weighted spin echo sequences (echo time, 12 milliseconds; repetition time, 600 milliseconds) were also taken. The slice thickness was 3 mm, interslice gap was 0.5 mm, and field of view was 140×140 mm with a 256×192 matrix. The patient, a 38-year-old woman, presented with a 1-month history of right upper eyelid blepharoptosis, right intraorbital pain, and headaches. Graves’ disease had been diagnosed 7 or 8 years previously, after which she was in a euthyroid state, with the slight elevation of her thyroid-stimulating antibody level. A Hess chart showed right inferior oblique muscle paresis (Fig 1A [figures available at http://aaojournal.org]). Sagittal (Fig 1B) and coronal (Fig 1C) T2-weighted magnetic resonance imaging findings clearly showed right inferior oblique muscle swelling. Compared with the coronal T1-weighted images (T1WIs) (Fig 1D), the inferior oblique muscle demonstrated slight inflammation. Although the right inferior and superior rectus muscles were also enlarged, a lesion of the levator palpebrae superioris muscle was unclear (data not shown). To reduce presumed muscle inflammation, steroid pulse therapy was undertaken (1000 mg/day of methylpredonisolone for 3 days, repeated the next week). Just after therapy, her right upper eyelid height settled to within normal limits, and her intraorbital pain and headaches were reduced. Three months after implementation of medication, her Hess chart also improved to almost within normal limits (Fig 2A). Sagittal T2WIs clearly showed that the inflammation of the inferior oblique muscle had resolved (Fig 2B). Judging from the coronal T2WI (Fig 2C) and T1WI (Fig 2D) findings, although signs of inflammation had disappeared, intramuscular adipose tissues were still increased. Other muscle lesions were also improved, but the contralateral inferior rectus muscle had become slightly enlarged (data not shown). Twelve months after therapy, the patient showed no recurrent symptoms of TAO. Coronal or axial T2WIs are usually useful for examining orbital involvement in TAO.3Kahaly G.J. Müller-Forell W. Förster G.J. et al.Imaging in Graves’ ophthalmopathy.in: Bahn R.S. Thyroid Eye Disease. Kluwer Academic Publishers, Boston2001: 137-162Crossref Google Scholar However, on these images inferior oblique muscle involvement will usually not be detected because it is anteriorly located in the orbit. However, if we carefully observe the inferior oblique muscle on coronal images, muscle swelling can be detected. As well, sagittal T2WI findings can more clearly demonstrate lesions of the inferior oblique muscle. We believe this is the first report of inferior oblique muscle involvement in TAO. Inferior oblique muscle involvement should be considered in patients with TAO.