Orbital pathology in thyroid-associated ophthalmopathy

Abstract

Thyroid-associated ophthalmopathy (TAO) is a disfiguring disease. The clinical symptoms are the consequence of inflammation in the orbital tissues in response to as yet unknown antigens, causing swelling of the extraocular muscles, edema and fibrosis, and subsequently eye movement impairment, exophthalmos and sometimes compression of the optic nerve. Analysis of orbits from 40 patients with Graves' ophthalmopathy showed an increased volume of both the extraocular muscles and the orbital adipose/connective tissue in 48%, increased muscle volume with normal adipose/connective tissue in 20% and normal muscles with increased adipose/connective tissue in 28%. The other orbits were normal (4%).

Knowledge of the overall anatomy and the distribution of immunocompetent cells may help to shed light on the pathophysiology of TAO. In normal orbital tissues B-lymphocytes were scarce, but T-lymphocytes were numerous in normal extraocular muscles, orbital connective tissue septa and in the loose connective tissue surrounding the adipose tissue. The most predominant cell type in normal extraocular muscles and in the orbital connective tissue is the macrophage. In TAO, irrespective of the activity state, significant increases in numbers of macrophages were found in the minor connective tissue septa and in the levator palpebrae/Miiller's muscle complex. In the latter muscle complex the number of macrophages per mm² is increased, whereas the number of HLA-DR⁺ cells is drastically reduced compared to controls. Overall these results show a shift in population from HLA-DRV macrophages, in control tissues, to HLA-DR7macrophages in orbital tissues obtained from patients with TAO.

Key Words:

• Thyroid-associated ophthalmopathy
• macrophage
• orbital anatomy
• T-lymphocyte