Makindo Medical Notes

Related Subjects: Temporal (Giant Cell GCA) Arteritis Tocilizumab

Giant cell arteritis (GCA) is a systemic arteritis that can cause preventable blindness if not treated promptly. It often presents in rheumatology, eye clinics, or stroke/TIA clinics. Approximately 20% of patients develop vision loss, which can be prevented with timely diagnosis and treatment.

About

• A vasculitis affecting mainly extracranial arteries
• Involves large and medium-sized arteries, typically in the external carotid system
• Predilection for external carotid, ciliary, and retinal arteries
• Risk of blindness is due to anterior ischaemic optic neuropathy
• Approximately 50% of patients may also present with symptoms of polymyalgia rheumatica (PMR)

Epidemiology

• Mean age of onset is 70 years
• Rarely occurs before age 50
• More common in Caucasians
• Female to male ratio is 3:1

Phenotypes

• Cranial (cGCA)
• Extracranial (ecGCA)
• Mixed (mixGCA)

Vessels Involved

• Intimal hyperplasia +/- thrombosis of the short posterior ciliary artery
• Posterior ciliary arteries are derived from the ophthalmic artery
• Ischaemia of extraocular muscles can cause diplopia
• The central retinal artery may also be involved

Aetiology

• Possibly an immune response to an unidentified antigen
• Endovascular damage and cytokine-mediated inflammation cause localized ischaemia
• Subacute granulomatous inflammation with giant cells
• Th1 cell-mediated immune response with elevated IL-6 levels
• HLA-DRB1 is associated with a higher risk of developing GCA

American College of Rheumatology Criteria for GCA

Clinical Presentation

• Fever, weight loss, malaise, and fatigue
• Monocular visual loss, possibly transient, resembling TIA
• Abrupt, often unilateral headache
• Temporal artery tenderness
• Jaw or tongue ache and claudication (due to masseter or lingual artery involvement)
• Ischaemic stroke is rare as the internal carotid artery is usually unaffected
• Blindness may occur due to posterior ciliary artery occlusion
• Late-stage complications: aortitis, aortic aneurysm, aortic dissection

Investigations

• FBC: Normocytic normochromic anaemia
• ESR: Typically >50 mm/h, often higher; CRP elevated; ALP elevated in 30% of cases
• Colour Duplex USS: Shows a hypoechoic halo (vessel oedema) and hourglass stenosis; these regress after 2 weeks of steroid treatment
• Gold Standard: Temporal artery biopsy (TAB) of an affected vessel. A long section is taken to account for skip lesions. Best performed within 2 weeks of diagnosis.
• Fluorescein Angiography: Diagnosis can be confirmed by demonstrating choroidal shutdown on fluorescein angiography.

Management

• If visual symptoms are present, refer to an eye hospital and start Prednisolone 1 mg/kg - often 60 mg/day immediately until diagnosis is confirmed or refuted. If no visual symptoms, refer to rheumatology or acute medicine. Start a PPI and bone protection with high dose steroids. Begin treatment prior to biopsy or USS results.
• Response to steroids is often rapid for generalized symptoms but is less effective once blindness occurs. Long-term management includes bone protection, diabetes screening, and other steroid-related issues in primary care. The steroid dose is gradually lowered over 18 months to 2 years.
• Tocilizumab may be used by a specialist. 162 mg once weekly SC, administer to abdomen, thigh or upper arm, for dose adjustments in patients with liver enzyme abnormalities, or low absolute neutrophil or platelet count—consult product literature, not to be used alone for acute relapses; review need for treatment beyond 52 weeks.

References

• Hassan N et al. Giant Cell Arteritis. BMJ 2011 May 23;342:d3019