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IGF-1R activation on orbital fibroblasts is a cause of the progression1
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Chapter 1: Pathophysiology of Thyroid Eye Disease (TED)
Thyroid Eye Disease, or TED, is a serious, progressive, and vision-threatening autoimmune disease. Emerging research demonstrates that the orbital fibroblast, a specialized cell responsible for tissue repair, is central to the pathophysiology of TED.1-4
Pathogenic orbital fibroblasts are believed to recruit fibrocytes and lymphocytes that infiltrate the orbit.4,5
Fibrocytes differentiate into orbital fibroblasts, which enhance T-cell proliferation and activation.2,4,6
T-cells and B-cells activate orbital fibroblasts and secrete cytokines, thyroid-stimulating hormone receptor, or TSHR, autoantibodies, and insulin-like growth factor-1 receptor, or IGF-1R, autoantibodies, which contribute to the inflammatory cascade.4,7
Two co-localized receptors reside on the surface of orbital fibroblasts: TSHR and IGF-1R, a gatekeeper of orbital fibroblast activation.2,4,8-10
Autoantibodies activate TSHR and IGF-1R, and cross talk mediated by beta-arrestin creates a receptor-signaling complex that stimulates orbital fibroblasts.4,11
Chapter 2: Inflammatory Cascade and Potential Consequences of TED
Once activated, orbital fibroblasts proliferate and produce inflammatory cytokines and hydrophilic hyaluronan, which enlarges orbital tissue volume.1,4
Activated orbital fibroblasts differentiate into adipocytes and myofibroblasts, which contribute, respectively, to adipogenesis and fibrosis of the orbital tissues.4,12
The ensuing tissue expansion and remodeling leads to crowding in the fixed bony orbit, and this may have long-term sequelae.4
Damage can include:
Cross talk between TSHR and IGF-1R, as well as IGF-1R-mediated immune function, may play a critical role in the pathophysiology of TED. Understanding the cross talk may be vital to addressing this debilitating disease.4,10,16
REFERENCES:
TARGETING IGF-1R ACTIVATION MAY HELP REDUCE INFLAMMATION AND PREVENT MUSCLE AND FAT TISSUE REMODELING, AS WELL AS EXPANSION BEHIND THE EYE.1
IN A STUDY OF PATIENTS DIAGNOSED WITH BOTH TED AND GRAVES’ DISEASE 71% (N=17) OF UNTREATED GRAVES' DISEASE PATIENTS WITH NO VISIBLE SIGNS OF TED SHOWED EXTRAOCULAR MUSCULAR SWELLING IN ORBITAL MRI10
Normal MRI13
Case courtesy of Mohd Radhwan Bin Abidin,
Radiopaedia.org, rID: 155793
Coronal T2 fat saturation MRI showing the superior (1), lateral (2), inferior (3), and medial (4) recti muscles and orbital fat (6) are normal in size. The optic nerve (5) appears normal.*
MRI with findings suggestive of moderate TED14
Case courtesy of Qutaiba Jaf'ar Mahmoud,
Radiopaedia.org, rID: 167879
Coronal T2 fat saturation MRI showing moderate enlargement and inflammation/edema of the superior (1), lateral (2), inferior (3), and medial (4) recti muscles and orbital fat (6) bilaterally. The optic nerve (5) appears normal.*
MRI with findings suggestive of severe TED15
Case courtesy of Roberto Schubert,
Radiopaedia.org, rID: 13874
Coronal T2 fat saturation MRI showing severe enlargement and inflammation/edema of the superior (1), lateral (2), inferior (3), and medial (4) recti muscles and orbital fat (6) bilaterally. There is also minimal crowding of the left optic nerve (5).*
*The numbers correspond with the numbers in the images above.
TREATING ONLY THE THYROID GLAND WON’T TREAT TED1-3,11
IGF-1R, insulin-like growth factor-1 receptor; MRI, magnetic resonance imaging; TSHR, thyroid-stimulating hormone receptor; T2, transverse relaxation time.