How is Giant Cell Arteritis (GCA) identified?

Identification of Giant Cell Arteritis (GCA)

Giant Cell Arteritis is identified through a combination of specific clinical features, laboratory findings, and confirmatory imaging or biopsy, with no single feature being sufficient to confirm or rule out the diagnosis. 1

Key Clinical Features

Symptoms with Highest Diagnostic Value

• Limb claudication (positive LR 6.01) - strongest clinical predictor 2
• Jaw claudication (positive LR 4.90) - highly specific symptom 2, 1
• New-onset persistent localized headache - common but only moderately sensitive 1

Physical Examination Findings

• Temporal artery thickening (positive LR 4.70) 2, 1
• Temporal artery loss of pulse (positive LR 3.25) 2, 1
• Temporal tenderness (positive LR 3.14) 2, 1

Laboratory Markers

Highly Informative Laboratory Tests

• Erythrocyte sedimentation rate (ESR)
  • ESR >100 mm/h (positive LR 3.11) 2, 1
  • Absence of ESR >40 mm/h (negative LR 0.18) - strongest negative predictor 2, 1
• C-reactive protein (CRP)
  • Absence of elevated CRP ≥2.5 mg/dL (negative LR 0.38) 2, 1
• Platelet count >400 × 10³/μL (positive LR 3.75) 2, 1

Demographic Risk Factors

• Age ≥50 years is essential (absence of age >70 has negative LR 0.48) 2, 1
• Female predominance (approximately 66.6% of cases) 2

Confirmatory Testing Algorithm

1. Initial Assessment: Evaluate clinical features and laboratory markers

   • If ESR <40 mm/h and CRP <2.5 mg/dL, GCA is unlikely (but not ruled out)
   • If multiple positive clinical features (especially jaw claudication, limb claudication) with elevated inflammatory markers, proceed to confirmatory testing

2. Confirmatory Testing:

   • Temporal artery biopsy (TAB): Highly specific but with imperfect sensitivity 1
   • Vascular imaging: 1, 3
     • High-resolution MRI of temporal and cranial arteries
     • Ultrasound of temporal and extracranial arteries
     • CT, MRI, or PET for large-vessel involvement

3. Optimal Imaging Algorithm: 3

   • Begin with high-resolution MRI, followed by either ultrasound or retinal angiography (for patients with ophthalmological symptoms) for highest diagnostic accuracy (100% sensitivity and specificity)

Diagnostic Pitfalls and Caveats

• No single feature is sufficient to confirm or rule out GCA when taken alone 2, 1
• Headache and scalp tenderness are common symptoms but have poor specificity in the suspected GCA population 1
• American College of Rheumatology 1990 criteria should not be used for clinical diagnosis (designed for research classification) 2
• Temporal artery biopsy can be negative in approximately 15% of cases due to the focal and segmental nature of inflammation 4
• Prompt diagnosis is critical as GCA is a medical emergency requiring immediate treatment to prevent permanent vision loss 1, 5

Urgent Management Considerations

• Immediate high-dose glucocorticoid therapy (40-60 mg/day prednisone-equivalent) should be initiated when GCA is strongly suspected, even before diagnostic confirmation, to prevent permanent vision loss 1
• Urgent referral (within 24 hours) to a hospital with a fast-track clinic is recommended for patients with suspected GCA, especially those with visual symptoms 1, 5
• Tocilizumab may be considered as a steroid-sparing agent in confirmed cases 1, 6

By systematically evaluating these clinical features, laboratory findings, and using appropriate confirmatory testing, clinicians can accurately identify GCA and initiate timely treatment to prevent serious complications such as permanent vision loss.