Key Facts

Giant cell arteritis is a granulomatous vasculitis predominantly affecting medium and large arteries, particularly branches of the external carotid artery. It is an ophthalmic emergency because untreated GCA can cause irreversible bilateral blindness. Treatment must not be delayed pending diagnostic investigations.

Epidemiology

• Incidence: 15-25 per 100,000 in those >50 years
• Peak age: 70-80 years; virtually never occurs before age 50
• Female:male ratio 2-3:1
• More common in Northern European and Scandinavian populations
• Associated with polymyalgia rheumatica (PMR) in 40-60% of cases

Aetiology

• Exact cause unknown; likely multifactorial
• Genetic susceptibility: HLA-DR4 association
• Possible infectious triggers (varicella zoster virus has been implicated)
• Environmental factors: higher incidence at northern latitudes, seasonal variation
• Ageing-related immune dysregulation with loss of immune tolerance

Pathophysiology

• Granulomatous inflammation of arterial media and adventitia
• CD4+ T-cell and macrophage-mediated immune response
• Dendritic cells in vasa vasorum present antigen, triggering T-cell activation
• Giant cells and granulomata form at the internal elastic lamina
• Intimal hyperplasia leads to luminal narrowing and thrombosis
• Ischaemia of supplied tissues causes symptoms (visual loss from posterior ciliary artery occlusion)
• Can affect aorta and its major branches (large-vessel GCA)

Cranial GCA

• New-onset headache: temporal, unilateral or bilateral, severe
• Scalp tenderness: pain on brushing hair, wearing glasses
• Jaw claudication: pain on sustained chewing (most specific symptom, LR+ 4.2)
• Temporal artery abnormalities: thickened, tender, non-pulsatile, nodular
• Constitutional symptoms: fever, malaise, weight loss, night sweats

Visual Manifestations

• Anterior ischaemic optic neuropathy (AION): sudden painless visual loss, altitudinal field defect, pallid disc oedema
• Amaurosis fugax: transient monocular visual loss (warning sign)
• Central retinal artery occlusion: sudden painless complete visual loss
• Diplopia: from ischaemia of extraocular muscles or cranial nerves (III, IV, VI)
• Posterior ischaemic optic neuropathy: rare

Red Flags

• Any visual symptoms (amaurosis fugax, visual loss, diplopia) — ophthalmic emergency
• Bilateral visual loss (indicates contralateral involvement)
• Jaw claudication with new headache in patient >50 years
• Sudden unexplained visual loss in elderly patient
• Tongue claudication or necrosis (rare but pathognomonic)

Bedside

• Visual acuity and visual fields
• Fundoscopy: pallid disc oedema (arteritic AION), cherry-red spot (CRAO)
• Palpation of temporal arteries: tenderness, thickening, reduced pulsation
• Blood pressure in both arms (large-vessel GCA)

Bloods

• ESR: typically >50mm/h (often >100mm/h); normal in 4%
• CRP: typically markedly raised; more sensitive than ESR
• FBC: normocytic anaemia, thrombocytosis common
• LFTs: raised ALP in 30%
• Fibrinogen: elevated

Imaging

• Temporal artery ultrasound: 'halo sign' (hypoechoic ring around vessel) — sensitivity 77%, specificity 96% (TABUL study)
• MRI/MRA: can demonstrate temporal artery wall thickening and enhancement
• PET-CT: for large-vessel GCA assessment (aortitis, large-vessel inflammation)
• CTA: if large-vessel involvement suspected

Special Tests

• Temporal artery biopsy (≥1cm, ideally within 2 weeks of starting steroids):
  • Gold standard; sensitivity 77-90% (skip lesions can cause false negatives)
  • Shows granulomatous inflammation, giant cells, fragmented internal elastic lamina
  • Should NOT delay treatment — biopsy remains positive for up to 2-4 weeks after starting steroids

Non-pharmacological

• Do NOT delay treatment — start steroids immediately on clinical suspicion
• Patient education: symptoms of relapse, importance of adherence
• Bone protection: calcium, vitamin D, consider bisphosphonate (NICE NG176)
• PPI for gastroprotection

Pharmacological

• Without visual symptoms: prednisolone 40-60mg OD (BSR 2020 guidelines)
• With visual symptoms or jaw claudication: prednisolone 60-100mg OD or IV methylprednisolone 500mg-1g daily for 3 days then oral
• Slow taper: reduce by no more than 10mg every 2 weeks once stable; typical treatment duration 18-24 months
• Aspirin 75mg OD: consider for vascular protection (debated)
• Tocilizumab (IL-6 receptor antagonist) 162mg SC weekly: recommended as steroid-sparing agent (GiACTA trial, NICE TA518)
  • Relapse-free remission at 52 weeks: 56% (tocilizumab) vs 14% (placebo)
• Methotrexate 10-15mg weekly: alternative steroid-sparing agent

Surgical

• Temporal artery biopsy (diagnostic, not therapeutic)
• Vascular surgery referral if aortic aneurysm (large-vessel GCA)

Referral Criteria

• Same-day ophthalmology assessment if visual symptoms
• Rheumatology referral for all suspected GCA
• Vascular surgery if large-vessel involvement
• Urgent biopsy within 2 weeks of starting steroids

• Visual loss at presentation is usually irreversible — recovery rate only 5-15%
• Without treatment, 50-65% with unilateral visual loss develop bilateral involvement within 1-2 weeks
• With prompt treatment, risk of further visual loss is <1%
• Relapse occurs in 40-60% during steroid taper
• Aortic aneurysm risk: 17.3× higher than general population; affects 10-20% of GCA patients
• Median treatment duration: 2-3 years for steroid taper
• Mortality is not significantly increased with appropriate treatment
• Steroid-related morbidity is significant: osteoporosis, diabetes, infections

ACR 1990 Classification Criteria for GCA (≥3 of 5)

GiACTA Trial Key Results

Steroid Tapering Schedule (BSR 2020)