Updates on the understanding and management of thyroid eye disease

Abstract

Thyroid eye disease (TED) is a complex disease associated with myriad clinical presentations, including facial disfigurement, vision loss, and decreased quality of life. Traditionally, steroid therapy and/or radiation therapy were commonly used in the treatment of active TED. While these therapies can help reduce inflammation, they often do not have a sustainable, significant long-term effect on disease outcomes, including proptosis and diplopia. Recent advances in our understanding of the pathophysiology of TED have shifted the focus of treatment toward targeted biologic therapies. Biologics have the advantage of precise immune modulation, which can have better safety profiles and greater efficacy compared to traditional approaches. For instance, the insulin-like growth factor-1 receptor (IGF-1R) has been found to be upregulated in TED patients and to colocalize with the thyroid-stimulating hormone receptor (TSHR), forming a signaling complex. Teprotumumab is an antibody targeted against IGF-1R. By inhibiting the IGF-1R/TSHR signaling pathway, teprotumumab may reduce the production of proinflammatory cytokines, hyaluronan secretion, and orbital fibroblast activation in patients with TED. Due to promising phase II and III clinical trial results, teprotumumab has become the first biologic US Food and Drug Administration (FDA)-approved for the treatment of TED. In addition, there are currently ongoing studies looking at the use of antibodies targeting the neonatal Fc receptor (FcRn) in various autoimmune diseases, including TED. FcRn functions to transport immunoglobulin G (IgG) and prevent their lysosomal degradation. By blocking the recycling of IgG, this approach may dampen the body's immune response, in particular the pathogenic IgG implicated in some autoimmune diseases. Advances in our understanding of the pathophysiology of TED, therefore, are leading to more targeted therapeutic options, and we are entering an exciting new phase in the management of TED. This review will cover recent insights into the understanding of TED pathophysiology and novel treatment options as well as ongoing studies of new potential treatment options for TED.

Keywords: Graves ophthalmopathy; biologics; targeted therapy; thyroid eye disease; thyroid-associated ophthalmopathy.

Figure 1.

Pathophysiology of thyroid eye disease. In TED, B-lymphocytes, T-lymphocytes, and CD34+ fibrocytes infiltrate the orbit. CD34+ fibroblasts, originating from bone marrow-derived fibrocytes, further differentiate into myofibroblasts or adipocytes. Both CD34+ and residential CD34− fibroblasts are present within the orbit, and depending upon microenvironment-mediated signaling, can produce cytokines, including IL-1β, IL-6, IL-8, IL-16, TNF-α, RANTES, and CD40 ligand, which activate orbital fibroblasts. CD34+fibroblasts express low levels of TSH-R, thyroglobulin, and additional thyroid antigens. TSIs activate the TSH-R/IGF-1R complex inducing inflammatory molecule expression and glycosaminoglycan synthesis. Furthermore, immunoglobulins directed against IGF-1R induce orbital fibroblast signaling, thereby increasing cytokine and hyaluronan production, and subsequent orbital tissue expansion, leading to proptosis and compression of the optic nerve. Adipogenesis also leads to orbital fat expansion. Abbreviations: IGF-1R, insulin-like growth factor-1 receptor; IL, interleukin; MHC, major histocompatibility complex; RANTES, Regulated on Activation, Normal T Cell Expression and Secreted); TED, thyroid eye disease; TGF-β, transforming growth factor beta; TNF-α, tumor necrosis factor alpha; TSH-R, thyroid-stimulating hormone receptor; TSI, thyroid-stimulating immunoglobulins.