Orbicularis Oculi Morphological Alterations in Affected and Nonaffected Sides in Hemifacial Spasm

Background: Although the nonaffected side appears to be clinically normal in hemifacial spasm (HFS), it is not known whether this side can be considered normal regarding histopathological findings. The purpose of this study was to objectively evaluate and compare orbicularis oculi samples of patients with HFS (not previously treated with botulinum toxin) and control patients undergoing cosmetic upper eyelid blepharoplasty. Methods: Orbicularis oculi samples from 22 eyelids were evaluated. There were 7 samples from the affected and 7 samples from the nonaffected sides of patients with HFS who had not been previously treated with botulinum toxin, and 8 samples from normal control patients. Muscle samples were prepared using hematoxylin and eosin staining, and a digital image analysis software was used for objective analyses. Results: When compared with normal controls, endomysial and perimysial connective tissue areas were significantly increased (P = 0.015) on the affected side in HFS, suggesting that this disorder is associated with chronic alterations that lead to muscle degeneration. Cell density was significantly reduced on the affected (P = 0.028) and also on the nonaffected sides in HFS (P = 0.003) compared with normal controls. This was observed, although, clinically, there were no signs or symptoms of increased muscular contraction on the nonaffected sides in any of the patients with HFS studied. Conclusions: Significant morphological differences in the orbicularis oculi muscle in patients with HFS were observed on both the affected and nonaffected sides. Our findings suggest a potential role for muscle homeostasis disturbances on both sides for patients with HFS. Affected sides in patients with HFS did, however, demonstrate muscle degeneration that was not present on the nonaffected sides.