Perhaps further clarification of the immunopathogenesis of GCA will point to new avenues for treatment, as has been the case with bench-to-bedside translations that have culminated in the modern management of rheumatoid disease. The past decade has seen solid progress in unraveling the complexities of T cell biology in GCA, led by Drs. Cornelia Weyand and Jorg Goronzy, professors of medicine at Stanford University in Palo Alto, Calif. Their work has shown that at least two separate lineages of CD4 T cells are functional in GCA, Th1 cells and Th17 cells, the signature cytokines of which are IFN-γ and IL-17, respectively. In GCA, CS suppress TH17 cells, but IFN-γ–producing Th17 cells persist.27 Whether suppression of these prolonged Th1 immune responses would be advantageous in the long-term management of GCA is still conjectural, but it is fundamental investigation of this sort will help to spotlight novel therapeutic targets.
PMR and GCA Considered
Despite the issues surrounding the management of PMR and GCA, we do have a dramatically effective treatment for PMR, in the form of low-dose CS, and an indisputably effective treatment for the prevention of blindness in GCA, the expeditious use of higher doses of CS. Yet PMR often goes unrecognized for weeks or months, and it is striking that the incidence of vision loss in patients with GCA has remained at about 15%, in one series after another, from the U.S. to Europe, over the past two decades.11,28-31 One major explanation for the latter, it seems likely, is that treatment has been delayed because symptoms have not been appropriately recognized.
PMR and GCA are common. The lifetime risk of PMR is only second to RA as a systemic rheumatic disease in U.S. adults, and in adults over the age of 50, the incidence of PMR is probably higher than that of RA.32 GCA is the most common systemic vasculitis by far.33 While awaiting further insights into the pathogenesis of PMR and GCA, better biomarkers for the their diagnosis and follow-up, better ways of managing CS in their treatment, and validation of better therapies, we must be conscientious in the more modest work of educating colleagues in other disciplines about these common systemic rheumatic diseases, so that, in turn, patients may reap the established benefits of timely diagnosis and efficacious treatment.
Dr. Docken is a senior physician at Brigham and Women’s Hospital and assistant professor of medicine at Harvard Medical School, both in Boston.
