Giant cell arteritis

Giant cell arteritis (GCA) is the most common primary systemic vasculitis in adults, affecting large and medium-sized arteries — predominantly the temporal artery, aorta, and its major branches. It almost exclusively affects individuals over 50 years of age, with peak incidence in the 7th and 8th decades. GCA is a rheumatological emergency due to the risk of irreversible vision loss from anterior ischaemic optic neuropathy. Prompt diagnosis and immediate treatment with high-dose corticosteroids is mandatory upon clinical suspicion.

Australian Epidemiology

GCA has an estimated incidence of 15–20 per 100,000 individuals over 50 years in Australia, predominantly affecting those of Northern European descent. Women are affected 2–3 times more frequently than men. Polymyalgia rheumatica (PMR) coexists in 40–60% of GCA cases. The ageing Australian population means GCA will become increasingly prevalent. Given the risk of permanent vision loss, GCA should be treated as an emergency in any patient presenting with relevant symptoms.

Granulomatous Arteritis

GCA is characterised by transmural granulomatous inflammation of the arterial wall, with giant cell formation, disruption of the internal elastic lamina, and intimal hyperplasia leading to luminal stenosis and occlusion. Dendritic cells within the adventitia activate CD4+ T cells, which differentiate into Th1 and Th17 cells producing IFN-γ and IL-17. This drives macrophage recruitment, giant cell formation, and vascular remodelling. TNF-α and IL-6 are key inflammatory mediators.

Vascular Consequences

Cranial involvement (temporal, ophthalmic, posterior ciliary arteries) causes ischaemia to the optic nerve, retina, and brain. Large-vessel involvement (aorta, subclavian, axillary arteries) leads to limb claudication, aortic aneurysm, and aortic dissection. Extracranial GCA without cranial symptoms is increasingly recognised, particularly on imaging.

Cranial GCA Symptoms

• New-onset headache — temporal, occipital, or diffuse; often severe and persistent
• Scalp tenderness — pain on combing hair or lying on pillow
• Temporal artery abnormality — thickened, nodular, tender, or pulseless temporal artery
• Jaw claudication — pain on chewing; highly specific for GCA
• Visual symptoms — amaurosis fugax, diplopia, sudden painless vision loss (ophthalmic emergency)
• Tongue claudication — pain on speaking/eating; rare but specific

Constitutional Symptoms

Fever (often low-grade), profound fatigue, weight loss, night sweats, and anorexia are common. PMR features (bilateral shoulder and hip girdle aching and stiffness) in 40–60% of patients.

Large-Vessel GCA

Arm claudication, blood pressure discrepancy between arms (>10 mmHg), bruits over subclavian/axillary arteries, absent radial pulse. Aortic involvement may present as aortic aneurysm or dissection years after diagnosis.

• Essential
  ESR

  Typically markedly elevated (>50 mm/hr; often >100 mm/hr). Normal ESR does not exclude GCA — present in 5% of biopsy-proven cases.
• Essential
  CRP

  More sensitive than ESR for disease activity. Typically >10 mg/L in active GCA. Useful for treatment monitoring.
• Essential
  Temporal Artery Biopsy (TAB)

  Gold standard for diagnosis. Sensitivity 70–85% (skip lesions reduce sensitivity). Obtain minimum 2 cm segment. Biopsy within 2 weeks of steroid start (histology preserved). Do not delay steroids for biopsy.
• Available
  Temporal Artery Ultrasound

  Non-invasive alternative/complement to TAB. Halo sign (hypoechoic wall thickening) highly specific for GCA. Operator-dependent; best in dedicated vasculitis ultrasound centres. Can guide biopsy site.
• Available
  PET-CT

  Detects large-vessel involvement (aorta, subclavian, axillary arteries). Not routinely required for cranial GCA but recommended if large-vessel disease suspected clinically.
• Available
  MRI Brain and Orbits

  For assessment of ischaemic complications (optic nerve ischaemia, stroke). Not diagnostic of GCA itself.

Initial Corticosteroid Therapy

Prednisolone 40–60 mg/day orally for uncomplicated GCA. IV methylprednisolone 500–1000 mg/day for 3 days for visual symptoms or established visual loss, then transition to prednisolone 60 mg/day. Do not delay steroids pending biopsy — histology remains interpretable for up to 2 weeks after steroid initiation.

Steroid Tapering

Reduce prednisolone by 10 mg every 2 weeks to 20 mg, then by 2.5 mg every 2–4 weeks to 10 mg, then by 1 mg every 4–8 weeks. Total duration typically 18–24 months. Many patients relapse during taper — do not taper faster than tolerated. Monitor ESR/CRP with each reduction.

Tocilizumab (IL-6 Receptor Inhibitor)

Tocilizumab 162 mg SC weekly is PBS-approved as a steroid-sparing agent in GCA. Reduces relapse rate and cumulative steroid exposure (GIACTA trial). Consider in patients with high steroid side-effect risk (diabetes, osteoporosis, obesity), relapsing disease, or inadequate steroid taper. Assess TB and hepatitis B status before initiation.

Low-Dose Aspirin

Low-dose aspirin 100 mg/day recommended to reduce cranial ischaemic events in GCA. Some evidence for reduction in vision loss and stroke risk. Continue alongside corticosteroids with gastroprotection.