Giant cell arteritis

Background

• Large-vessel vasculitis that occurs in older age and is associated with polymyalgia rheumatica
• Also known as temporal arteritis

Epidemiology

• Most common systemic vasculitis in North America

Pathophysiology

• Granulomatous inflammation of the aortic arch and extracranial carotid artery

Clinical Manifestations

• After 50 years
• Headache, usually unilateral with tenderness
• Polymyalgia rheumatica (PMR)
• Jaw claudication
• Visual loss

Prognosis

• Cycles of flares and remissions requiring adjustment in prednisone
• Very few can safely taper off of steroids altogether

Investigations

• Temporal artery biopsy
  • Shows mononuclear cell infiltrate with granulomatous inflammation, and usually multinucleated giant cells
  • Findings are still visible 6-12mo after starting therapy
• Ultrasound of temporal arteries
  • Looking for "halo sign" of hypoechoic ring around Doppler flow
  • Sn 55-100%, Sp 78-100% (more specific than sensitive)
  • Disappears quickly with treatment
• MRI scalp arteries

McMaster Workup

• Initial investigation with ultrasound; if positive halo sign, can skip the rest
• Low or moderate
  • Scalp artery MRI
    • Normal: treat based on MD diagnosis
    • Abnormal
      • Temporal artery biopsy
        • Negative: treat based on MD diagnosis (biopsy-negative GCA or other)
        • Positive: treat as GCA
• High
  • Temporal artery biopsy
    • Negative: treat based on MD diagnosis (biopsy-negative GCA or other)
    • Positive: treat as GCA

ACR Classification Criteria

• Requires 3 of 5 criteria
  • Age ≥50 years
  • New localized headache
  • Temporal artery tenderness or decreased temporal artery pulse
  • ESR ≥ 50 mm/h: 10-20% false negative, though
  • Artery biopsy consistent with GCA: Up to 40% false negative, related to skip lesions, small biopsies, or lack of temporal artery involvement
• Not diagnostic criteria

Management

• Prednisone 0.2-0.3mg/kg/day (and appropriate screening)
  • Taper over 2 years, dropping by 5mg/d over a few weeks then slowing down
  • Often aren't able to taper off altogether
• Low-dose ASA for cardiovascular and cerebrovascular protection
• Can consider adding steroid-sparing agent
  • Tocilizumab (IL-6 receptor)
  • Maybe methotrexate
  • Not MMF or other DMARDs
• Follow ESR for response
• Annual chest x-rays for the first ten years, to monitor for thoracic aortic aneurysm