A Case of Surgical Diagnosis and Treatment of Idiopathic Orbital Myositis with Sudden Vision Loss

PURPOSE: We report a case of idiopathic orbital myositis with sudden onset of unilateral visual loss and hypertrophy of the lateral rectus muscle at the apex of the orbit that was diagnosed using orbital biopsy and treated with intravenous corticosteroids. CASE SUMMARY: We examined a 20-year-old woman who complained of decreased visual acuity and binocular diplopia for 2 weeks. She showed 40-prism diopter left esotropia at the primary position. Her visual acuity with eyeglasses was 0.7 and 0.2 in the right and left eyes, respectively. Brain magnetic resonance imaging (MRI) revealed a round mass on the left lateral rectus muscle at the apex of the orbit with optic nerve compression. We planned orbital biopsy to exclude orbital lymphoma and other biopsy-requiring diseases. After 3 weeks, the visual acuity of her left eye decreased to 0.02. Repeated MRI revealed enlargement of all extraocular muscles on the left orbit. With biopsy showing several lymphocytes infiltrating muscle fibers, we made a diagnosis of idiopathic orbital myositis. Intravenous injection of corticosteroids was administered during hospitalization. After 2 weeks of corticosteroid therapy, the visual acuity of her left eye was improved to 0.63, the esotropia disappeared, and the enlargement of the left lateral rectus muscle was improved on orbital MRI. CONCLUSIONS: For non-specific idiopathic orbital myositis located at the apex of the orbit and enlargement of the extraocular muscle in a short period with decreased visual acuity, administration of intravenous injection of corticosteroids before orbital biopsy could help restore vision.

Density of Orbital Fat and Extraocular Muscle in Thyroid-Associated Myopathy and Idiopathic Orbital Myositis

PURPOSE: To perform and compare differential diagnosis of patients with thyroid-associated myopathy, idiopathic orbital myositis and normal controls based on orbital computed tomography. Orbital fat and extraocular muscle densities were quantified using Hounsfield Unit (HU) and their characteristics were compared and analyzed. METHODS: From February 2005 to January 2013, orbital computed tomography was performed on 90 eyes of 47 thyroid-associated myopathy patients, 18 eyes of 14 idiopathic orbital myositis patients and 280 eyes of 140 normal subjects. The average values of orbital fat and extraocular muscle densities were measured and compared using HU. The density differences between the patients with thyroid-associated myopathy and the normal group were analyzed by age, clinical activity score, ocular protrusion and disease duration. RESULTS: In the thyroid-associated myopathy group, orbital fat and extraocular muscle densities were -87.8 +/- 12.5 HU and 48.7 +/- 7.1 HU, respectively. In the idiopathic orbital myositis group, the orbital fat and extraocular muscle densities were 79.9 +/- 9.9 HU and 49.2 +/- 9.1 HU, respectively. There was a statistically significant lower result of orbital fat in the thyroid-associated myopathy group (p = 0.002), however, the extraocular muscle density did not show a statistically significant difference (p = 0.775). The orbital fat and extraocular muscle densities of the normal group were -79.0 +/- 11.2 HU and 54.3 +/- 6.3 HU, respectively. There were significantly lower results in both orbital fat and extraocular muscle densities in the thyroid-associated myopathy group than normal group (p = 0.000). In active cases and those accompanied by ocular protrusion, there was no significant difference in orbital fat density (p = 0.345 and p = 0.952, respectively), while extraocular muscle density significantly decreased (p = 0.007 and p = 0.003, respectively). CONCLUSIONS: A difference between the orbital fat and extraocular muscle densities in thyroid-associated myopathy and idiopathic orbital myositis could be quantitatively found using HU and orbital computed tomography.