Other vessels that may display increased metabolic activity include the brachiocephalic trunk, axillary arteries, carotid arteries, iliac arteries and femoral arteries. A small meta-analysis has suggested that PET has a positive predictive value of 0.85 (95% CI 0.62, 0.95) and a negative predictive value of 0.88 (95% CI 0.72, 0.95) for the diagnosis of large-vessel vasculitis.10
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Explore This IssueMarch 2015
Although the utility of cross-sectional arterial imaging for the diagnosis of GCA is high, a limited amount of research exists regarding the usefulness of vascular radiology for the purpose of evaluating response to treatment, disease activity, risk of disease flare or likelihood of long-term large-vessel complications (e.g., aneurysm or stenosis). Further, vascular imaging is expensive, not always covered by insurance companies for the purpose of large-vessel vasculitis care, and in some regions its use is confined to large academic hospitals. Further study of these imaging modalities for the purpose of assessing treatment response is required.
An Effective Treatment Strategy
GCA carries a substantial morbidity burden related not only to the disease itself but also to its therapy. CS, the mainstay of treatment for GCA, effectively control the symptoms of systemic inflammation and prevent acute damage (i.e., vision loss) in most patients, but generally fail to cure the disorder or induce sustained remissions. Current standards of care generally require lengthy courses of CS, on the order of a minimum of one year in most cases. Unfortunately, 40–80% of GCA patients relapse following the cessation of CS and prove to require much longer courses of these medications. The well-known adverse effects of CS—weight gain, diabetes mellitus, hypertension, osteoporotic fragility fractures, cataracts, gastrointestinal bleeding, infection, skin bruising and mood changes—are likely to be accentuated among the predominantly elderly and female GCA patient population.11
No clear alternative to long-term treatment with CS has been defined for GCA. Unfortunately, clinical trials of immunosuppressive medications, including methotrexate and tumor necrosis factor (TNF)–α antagonists, have shown mixed results or been unsuccessful.
New Targets for Therapy
The etiology of GCA remains elusive. However, research suggests that two distinct pathways driven by T helper (Th) 17 and Th1 lymphocytes, and a suppressed regulatory T-cell response contribute to disease pathogenesis.12 Whereas prednisone has been shown to correct abnormalities described in the Th17 axis of untreated patients, reports regarding the effects of CS on the upregulated Th1 response are contradictory.12,13,14 Moreover, decreased numbers of regulatory T cells are seen in the bloodstream of patients regardless of disease activity or CS treatment.14