Radiological Characteristics of Extraocular Muscles in Myasthenia Gravis Patients with Ocular Manifestations: A Case–Control Study

Abstract

Purpose To analyze radiological characteristics of the extraocular muscles (EOMs) in myasthenia gravis (MG) patients with ocular manifestations. Patients and Methods This retrospective case–control study included all MG cases with ocular manifestations, who attended a neuro-ophthalmology clinic at a university hospital, Bangkok, from April 2009 to June 2018. They experienced double vision and ophthalmoplegia. Control participants had normal eye movements. Orbital scans were thoroughly reviewed. We measured muscle thickness (MT) of the superior rectus, inferior rectus, medial rectus and lateral rectus muscles in both eyes using magnetic resonance imaging or computed tomography scan. The sum of the muscle thickness at all sites was calculated (MTsum). Comparisons of the mean MT of each muscle type and the mean MTsum between the MG and control groups were performed by using Student’s t -test. MRI signal intensities of the EOMs were also recorded. Results Twenty MG cases and 20 controls were included in the study. The mean MTsum was 23.7 (standard deviation 4.8) mm in the MG group and 32.6 (3.5) mm in the controls. There were statistically significant differences between the two groups with respect to the mean MT and mean MTsum (p <0.001). In the MG group, there was a negative correlation between the MTsum and disease duration (p= 0.03). By using coronal T2-weighted orbital MRI with fat suppression (T2W/FS), the most frequent finding was isointensity with central hypointensity of the EOMs in the MG group. Conclusion Atrophic EOMs were frequently found in the MG group, particularly in chronic cases. Isointensity with central hypointensity of EOMs on T2W/FS was also common in the MG group. These findings highlight the importance of muscle involvement in MG and may be helpful for clinical decision-making.

The Epidemiology and Phenotypes of Ocular Manifestations in Childhood and Juvenile Myasthenia Gravis: A Review

“…Similar to the EOM histopathological findings, imaging of the EOMs in patients with MG with chronic refractory ocular symptoms, found evidence of muscle atrophy and fatty replacement ( 52 ). Interestingly, fatty replacement with larger muscle volume was evident in the EOMs of a pilot case series (feasibility study) earlier in their disease course ( 68 ), whereas those with a longer disease duration showed muscle atrophy ( 69 ).…”

Extraocular Muscle Atrophy in Myasthenia Gravis

“…[ 1 2 3 ] However, three recent studies have revealed that fat replacement and atrophy are not so uncommon in these muscles. [ 4 5 6 ] MG related to anti-MuSK antibodies is known to cause atrophy of the tongue and facial muscles. However, extraocular involvement was not extensively reported.…”

“…Lueangaram et al . [ 4 ] showed a statistically significant difference in the muscle volumes of an MG group compared to a control group. Moreover, the atrophy of extraocular muscles in MG was more in chronic cases, although it occurred early in some.…”

“…One possible mechanism is the persistent inflammation leading to the damage of motor endplates, resulting in the denervation and fibrosis of muscles. [ 3 4 8 ] The ocular motility might not improve with treatment in such instances. [ 3 ] Our patient also had a persistent limitation of the extraocular movements, which was unresponsive to the treatment.…”

Clinical and imaging clues to the diagnosis and follow‐up of ptosis and ophthalmoparesis

“…44,77,97 In CPEO, an increase in signal intensity on a T1w scan has been described within EOM, 81 as well as a quantitative increase in T2 relaxation time, 80 89 In addition, central hypo-intensities were observed on T2w scans with fat suppression in myasthenia gravis. 90 In myasthenia gravis, fat replacement appears to be less frequently reported in literature than in CPEO. In CFEOM Type II, T1w imaging shows bright signal regions and longitudinal fissures in the LR and the MR, also indicative of fat replacement.…”