What are the diagnostic criteria for Giant Cell Arteritis (GCA)?

Diagnostic Criteria for Giant Cell Arteritis (GCA)

No single feature is sufficient to confirm or rule out GCA, and diagnosis requires a combination of clinical features, laboratory findings, and confirmatory testing through temporal artery biopsy or vascular imaging. 1

Clinical Features with Highest Diagnostic Value

Symptoms and Demographics

• Age >70 years (absence has negative LR 0.48) 1
• Jaw claudication (positive LR 4.90) 1
• Limb claudication (positive LR 6.01) 1
• New headache (common but not highly specific) 1
• Scalp tenderness 1
• Polymyalgic symptoms (muscle pain and stiffness) 1
• Systemic symptoms: weight loss, fatigue, fever 1

Physical Examination Findings

• Temporal artery abnormalities:
  • Temporal artery thickening (positive LR 4.70) 1
  • Temporal artery loss of pulse (positive LR 3.25) 1
  • Temporal tenderness (positive LR 3.14) 1
• Visual disturbances including anterior ischemic optic neuropathy (positive LR 2.15) 1

Laboratory Findings

• ESR elevation:

  • 100 mm/h (positive LR 3.11) 1

  • 40 mm/h (absence has negative LR 0.18) 1

• CRP elevation:
  • ≥2.5 mg/dL (absence has negative LR 0.38) 1
• Thrombocytosis: platelet count >400 × 10³/μL (positive LR 3.75) 1

Diagnostic Algorithm

1. Initial Assessment: Evaluate for clinical features and inflammatory markers

   • Age >50 years (mandatory consideration)
   • Presence of cranial symptoms (headache, jaw claudication, visual disturbances)
   • Elevated inflammatory markers (ESR and CRP)

2. Laboratory Testing:

   • ESR (critical test - absence of elevation >40 mm/h makes GCA unlikely)
   • CRP (absence of elevation makes GCA unlikely)
   • Complete blood count (check for thrombocytosis)

3. Confirmatory Testing (should be performed in all suspected cases):

   • Temporal artery biopsy: Gold standard with high specificity but imperfect sensitivity 1
   • Vascular imaging (alternatives or complementary to biopsy):
     • Ultrasound (look for "halo" and "compression" sign) 1
     • MRI
     • PET-CT
     • Contrast-enhanced CT

Important Considerations

Diagnostic Pitfalls

• Do not rely solely on ACR 1990 classification criteria for clinical diagnosis (these were developed for research purposes) 1, 2
• Normal inflammatory markers do not rule out GCA: While rare (0.8% of cases), GCA can occur with normal ESR and CRP 3
• Segmental involvement: Due to the focal nature of arterial inflammation, temporal artery biopsy may be negative in approximately 15% of cases 4
• Pre-biopsy steroid treatment: Do not withhold treatment while awaiting biopsy if clinical suspicion is high, as vision loss can occur rapidly 5

Treatment Implications

• Prompt diagnosis is critical as GCA is a "do-not-miss" diagnosis that can lead to irreversible vision loss if untreated 1
• High-dose glucocorticoids are the cornerstone of initial treatment 6
• Tocilizumab has demonstrated efficacy in reducing glucocorticoid requirements and flare rates 1, 7

Summary of Diagnostic Approach

1. High clinical suspicion based on age >50 years plus cranial symptoms
2. Laboratory confirmation with elevated inflammatory markers (ESR/CRP)
3. Definitive diagnosis through temporal artery biopsy and/or vascular imaging
4. Immediate treatment with high-dose glucocorticoids if clinical suspicion is high, even before confirmatory testing results

Remember that no single feature is pathognomonic for GCA, and the diagnosis requires a combination of clinical, laboratory, and imaging/histopathological findings.