Background: To investigate the incidence of absent Bell's phenomenon (BP) and the relationship between absent BP and inferior rectus muscle hypertrophy and other clinical features in patients with thyroid eye disease (TED).
Methods: A total of 104 patients who were first diagnosed with TED between January and December 2014 were included. Inferior rectus muscle area and associations with clinical features of TED and thyroid function test including thyroid specific antibodies were compared between patients with TED with and without BP. The volume of the inferior rectus muscle was calculated by adding up all the cross-sectional areas measured on sagittal CT images.
Results: Among the 104 patients, 14 had absent BP (13.5%), 12 with bilateral and two with unilateral. There was no significant difference in thyroid function test, presence of TSIs, exophthalmos, or volume of inferior rectus muscle measured in CT scans (P > 0.05). Incidence of diplopia, elevation limitation, and upper eyelid retraction were risk factors of absent BP in TED patients (by logistic regression analysis, P < 0.05).
Conclusions: Inferior rectus muscle hypertrophy was not the cause of absent BP in TED patients. Fibrosis and tightening of the inferior rectus muscle, lower eyelid, and surrounding orbital tissues, rather than inferior rectus muscle hypertrophy, might be related to absent BP in TED patients.
Keywords: Bell’s phenomeon; Fibrosis; Inferior rectus muscle; Thryoid eye disease.
© 2021. The Author(s).