What are the diagnostic criteria for giant cell arteritis?

Diagnostic Criteria for Giant Cell Arteritis

No single clinical or laboratory feature is sufficient to diagnose giant cell arteritis (GCA); a combination of symptoms, physical signs, laboratory tests, and confirmatory testing (temporal artery biopsy or vascular imaging) is required for diagnosis. 1

Key Clinical Features with Strong Diagnostic Value

Symptoms with Highest Positive Likelihood Ratios

• Limb claudication (LR+ 6.01) 1
• Jaw claudication (LR+ 4.90) 1 - consistently one of the strongest predictors across multiple studies 2, 3
• Neck pain (LR+ 3.4) 3
• New-onset headache (OR 6.0) 2

Physical Examination Findings

• Temporal artery thickening (LR+ 4.70) 1
• Temporal artery loss of pulse (LR+ 3.25) 1
• Temporal artery tenderness (LR+ 3.14) 1

Laboratory Findings

• Elevated platelet count >400 × 10³/μL (LR+ 3.75) 1, 2
• ESR >100 mm/h (LR+ 3.11) 1
• CRP >2.45 mg/dL (LR+ 3.2) 3

Findings That Help Rule Out GCA

• Absence of ESR >40 mm/h (LR- 0.18) 1
• Absence of CRP >2.5 mg/dL (LR- 0.38) 1
• Age <70 years (LR- 0.48) 1

Diagnostic Algorithm

1. Initial Assessment: Evaluate for key symptoms (jaw claudication, new headache, limb claudication, neck pain) and physical findings (temporal artery abnormalities)

2. Laboratory Testing:

   • ESR and CRP (both should be obtained)
   • Complete blood count with platelet count
   • Note: CRP has higher sensitivity (100%) than ESR (92%) for GCA detection 3

3. Confirmatory Testing:

   • Temporal artery biopsy (TAB): Remains the gold standard for diagnosis 4
     • Should be at least 1 cm in length
     • Multiple sectioning recommended due to skip lesions
     • Positive finding: vasculitis with mononuclear cell inflammatory infiltrates, often with giant cells 5
   • Vascular imaging: When biopsy is negative or not feasible
     • Color duplex ultrasonography of temporal arteries
     • MRI or PET for extracranial disease

4. Diagnostic Decision:

   • Positive biopsy: Confirms diagnosis
   • Negative biopsy: Diagnosis may still be made clinically if patient meets American College of Rheumatology criteria and has strong clinical features 5

Important Considerations and Pitfalls

• Biopsy limitations: Due to the focal and segmental nature of GCA, approximately 15% of biopsies may be negative despite the presence of disease 5

• Corticosteroid treatment: Prior steroid use does not significantly decrease the likelihood of a positive biopsy finding in the short term 6, but biopsy should ideally be performed promptly

• Age requirement: GCA occurs exclusively in individuals older than 50 years, with incidence increasing with age 5

• Common diagnostic pitfalls:

  • Relying solely on headache (poor specificity in suspected GCA population) 1
  • Dismissing diagnosis due to normal ESR (can occur in some cases)
  • Failing to consider GCA in patients with constitutional symptoms (weight loss, fever) without classic cranial features 6
  • Using ACR classification criteria for diagnosis (these were developed for research purposes, not clinical diagnosis) 1, 5

• Combined approach: Using both ESR and CRP together provides the best specificity (97%) 3

Remember that GCA is a "do-not-miss" diagnosis as prompt treatment can prevent irreversible visual loss. When clinical suspicion is high, treatment should be initiated while awaiting confirmatory testing results 1.