What are the diagnostic tests for giant cell arteritis?

Diagnostic Tests for Giant Cell Arteritis

For patients with suspected giant cell arteritis (GCA), temporal artery biopsy is conditionally recommended over magnetic resonance imaging (MRI) of the cranial arteries for establishing a diagnosis, though noninvasive vascular imaging should be used when biopsy results are negative. 1

Initial Diagnostic Approach

Laboratory Tests

• Erythrocyte sedimentation rate (ESR)
  • Elevated ESR >100 mm/h has a positive likelihood ratio of 3.11
  • Absence of ESR >40 mm/h has a negative likelihood ratio of 0.18 2
• C-reactive protein (CRP)
  • Elevated CRP ≥2.5 mg/dL is supportive
  • Absence of elevated CRP has a negative likelihood ratio of 0.38 2
• Complete blood count (CBC)
  • Platelet count >400 × 10³/μL has a positive likelihood ratio of 3.75 2

Temporal Artery Biopsy

• Gold standard diagnostic test for GCA 1
• Should be performed even after initiation of glucocorticoid therapy
• Biopsy shows vasculitis with mononuclear infiltrate and multinucleated giant cells 2
• Important: Negative biopsy does not rule out GCA due to skip lesions

Noninvasive Vascular Imaging

• Recommended when temporal artery biopsy is negative but clinical suspicion remains high 1
• Options include:
  • MRI or CT angiography of neck/chest/abdomen/pelvis
  • Ultrasonography (particularly of temporal arteries)
  • 18F-fluorodeoxyglucose positron emission tomography (FDG-PET) 1

Diagnostic Algorithm

1. Clinical Assessment

   • Age ≥50 years (absence of age >70 has negative likelihood ratio of 0.48) 2
   • New-onset persistent localized headache
   • Jaw claudication (positive likelihood ratio: 4.90)
   • Scalp tenderness (positive likelihood ratio: 3.14)
   • Temporal artery abnormalities:
     • Thickening (positive likelihood ratio: 4.70)
     • Tenderness
     • Loss of pulse (positive likelihood ratio: 3.25) 2
   • Visual symptoms (emergency requiring immediate treatment)
   • Constitutional symptoms (fever, weight loss, fatigue)

2. Laboratory Testing

   • Order ESR, CRP, and CBC with platelets

3. Temporal Artery Biopsy

   • Perform even after initiating treatment
   • Positive result confirms diagnosis

4. If Biopsy Negative but Clinical Suspicion Remains High

   • Proceed with noninvasive vascular imaging to detect large vessel involvement 1

Important Considerations

• Treatment should not be delayed for diagnostic testing when GCA is strongly suspected, especially with visual symptoms 3, 4
• Initiate high-dose glucocorticoids immediately to prevent permanent vision loss 2
• Referral to an experienced center is recommended for further workup, including large-vessel imaging 2

Pitfalls to Avoid

• Delaying treatment while waiting for diagnostic confirmation can lead to irreversible vision loss 5
• Relying solely on ESR/CRP, as normal values don't exclude GCA
• Assuming a negative temporal artery biopsy rules out GCA
• Failing to consider large-vessel involvement when cranial symptoms are absent
• Inadequate biopsy length (should be at least 1-2 cm)
• Overlooking GCA in patients with atypical presentations or predominant polymyalgia rheumatica symptoms

The diagnostic approach to GCA requires a high index of suspicion, prompt laboratory testing, temporal artery biopsy as the primary diagnostic test, and supplementary vascular imaging when necessary. Early diagnosis and treatment are crucial to prevent permanent vision loss and other ischemic complications.