Giant-cell arteritis (GCA) is a medium-to-large vessel vasculitis. It has a predilection for the cranial branches of arteries arising from the aortic arch, but has the potential for systemic involvement. Diagnosis is based on a variety of clinical, biochemical and histological features as outlined by the American College of Rheumatology (ACR) in 1990 (see Table 1).¹ The presence of three of the five criteria has a sensitivity of 93.5% and a specificity of 91.2%¹ for the diagnosis. The approach to GCA is evolving with the advent of increasingly sophisticated techniques. In line with this, the European League Against Rheumatism (EULAR) published recommendations in 2008 based on all available evidence and expert consensus.²

Table 1: ACR criteria for diagnosis of GCA(click to enlarge)

Non-invasive diagnosis

Since the introduction of multi-modality vascular imaging, there has been an interest in non-invasive diagnostic techniques. There are several characteristic ultrasonographic features including the hypoechoic ‘halo’ sign. Meta-analysis suggests that ultrasonography has high diagnostic yield.³ It is, by definition, user-dependent, and so its strength and reproducibility as a diagnostic tool must be evaluated in multi-centre trials prior to general use. 

The role of magnetic resonance angiography (MRA) has not been clarified although it has a potential role in guiding temporal artery biopsies and assessing large vessel involvement.⁴ Positron emission tomography (PET) is also in its early stages of evaluation as a diagnostic modality.^5,6

Invasive diagnosis

Temporal artery biopsy remains the gold standard diagnostic technique. Although recommended in all possible GCA cases,² it is unlikely to help in cases that do not meet the ACR criteria for diagnosis.⁷ In most published series, about one-third of temporal artery biopsies yield positive results.⁷ Therefore, it is recommended that a unilateral sample at least one centimetre in length be taken.²

Treatment

It is vital that the biopsy does not delay treatment.^8,9 Due to the possibility of a false negative result, and the risk of irreversible ocular damage, treatment should begin immediately when there is strong clinical suspicion of GCA.¹¹

Glucocorticoid therapy

Early, intensive high-dose steroid therapy is the mainstay of treatment in GCA.¹² Intravenous methylprednisolone may benefit patients presenting with visual symptoms, preventing progression to irreversible visual loss.^10,13 The optimal dose of glucocorticoids for initial treatment of GCA is uncertain. An initial dose of prednisolone 1mg/kg/day (maximum 60mg/day) is almost always used.¹³

Once the disease has been controlled adequately, tapering of glucocorticoid should begin. This usually starts two to four weeks after the initiation of prednisolone. A moderate dose of steroid such as 10-15mg/day is favourable at two to three months.^15,16 Tapering should not be in the form of alternate day therapy as this is more likely to lead to a vasculitis relapse.¹⁴ Treatment length is mainly dictated by response to therapy and disease flare, and can vary. Adverse effects of glucocorticoids should be anticipated and patients told about them. Prophylaxis against steroid-induced osteoporosis is always recommended.¹⁷

Immunosuppressive therapy 

To minimise the long-term steroid side-effects, steroid-sparing strategies have been evaluated in recent times.¹³ There have been three small randomised controlled trials (RCTs) evaluating methotrexate as adjunctive therapy to glucocorticoid.^15,18,19 A meta-analysis of these three trials demonstrated some benefit for methotrexate (10-15mg/week) in reducing the relapse rate and lowering the cumulative dose of glucocorticoid therapy.²⁰ Although GCA has been characterised by granulomatous inflammation, anti-tumour necrosis factor (TNF) agents such as infliximab have shown no therapeutic benefit to date.²¹

Antiplatelet therapy

Patients with GCA are at an increased risk of developing cardiovascular and cerebrovascular events.^22,23 The addition of low-dose antiplatelet agents such as aspirin (75-150mg/day) protects against such events and, in the absence of contraindications, should be prescribed to all patients.²⁴

References

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2. EULAR recommendations for the management of large vessel vasculitis. Ann Rheum Dis 2009; 68: 318–323
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