Clinicopathologic Evaluation of the Mueller Muscle in Thyroid-Associated Orbitopathy

Abstract

Contrary to previous reports, the Mueller muscle is involved in the inflammation and fibrosis that characterizes thyroid-associated orbitopathy. The Mueller muscle is grossly enlarged. On histopathologic inspection, fibrosis, fatty infiltration, and increased mast cell presence accompany focal atrophy of the Mueller muscle. In concordance with prior descriptions, many Mueller cells are in an actively contracting state on electron microscopy.