The pathogenesis of this illness is summarized in three main
phenomena: (1) inflammation of the periorbital soft tissues;
(2) overproduction of glycosaminoglycans by orbital fibroblasts;
and (3) hyperplasia of adipose tissue [1]. Along with
the orbital fibroblasts, the perimysium fibroblasts proliferate,
producing collagen and glycosaminoglycans in the extracellular
matrix. The polyanionic charge and the extremely
high osmotic pressure of this matrix substance render it
highly hydrophilic and increase its capacity to retain water.
As a consequence, the extraocularmuscles swell dramatically
[9]. Several clinical manifestations of GO are caused by an
increase in the orbital soft tissue volume which leads to a
higher pressure within the inexpandable bone cavity. The
periorbital edema is primarily congestive and it probably
reflects a decrease in venous draining due to compression
in the orbital space [10]. Conversely, development of new
fat cells (adipogenesis) is also a cause of increased orbital
tissue volume.The orbit contains different subpopulations of
fibroblasts exhibiting phenotypic heterogeneity.This implies
important functional consequences from the cellular diversity
and provides evidence suggesting divergent biological
roles for fibroblasts within the extraocular muscles and
fibroblasts from the adipose tissue. The first ones, when
exposed to cytokines, can differentiate into myofibroblasts
and then participate in inflammation, repair, and fibrosis.
On the other hand, half of the fibroblasts within the adipose
tissue are preadipocytes that, under certain conditions, can be
induced to differentiate.When prompted by the constellation
of growth factors and cytokines that are expressed as a
consequence of GO, these cells may undergo differentiation
into adipocytes and thus contribute to the increased tissue
volume associated with the disease [11, 12].
In most cases, GO develops with only one inflammatory
onset (active phase), which is followed by a phase of stillness
(inactive phase). In the inactive phase, the long lasting
muscular edema along with the increased