What are the recommended diagnostic steps for temporal arteritis?

Diagnostic Steps for Temporal Arteritis

For patients with suspected temporal arteritis, temporal artery biopsy remains the diagnostic test of choice in the United States, with additional large vessel imaging recommended if the biopsy is negative but clinical suspicion remains high. 1, 2

Clinical Evaluation

Key Symptoms and Signs to Assess

• Highly Specific Features:
  • Jaw claudication (positive likelihood ratio: 4.90)
  • Limb claudication (highest positive likelihood ratio: 6.01)
  • Temporal artery thickening (positive likelihood ratio: 4.70)
  • Temporal artery loss of pulse (positive likelihood ratio: 3.25)
  • New-onset persistent localized headache (moderate sensitivity)
  • Scalp tenderness
  • Visual disturbances (including amaurosis fugax, diplopia)

Laboratory Testing

• Essential Laboratory Tests:
  • Erythrocyte sedimentation rate (ESR)
    • ESR >100 mm/h has positive likelihood ratio of 3.11
    • Absence of ESR >40 mm/h has negative likelihood ratio of 0.18
  • C-reactive protein (CRP)
    • CRP ≥2.5 mg/dL has positive predictive value
    • Absence of elevated CRP has negative likelihood ratio of 0.38
  • Complete blood count with platelets
    • Platelet count >400 × 10³/μL has positive likelihood ratio of 3.75

Diagnostic Algorithm

1. Initial Assessment:

   • Evaluate clinical features and laboratory markers
   • Start high-dose glucocorticoids immediately if high clinical suspicion (especially with visual symptoms)

2. Temporal Artery Biopsy:

   • Obtain within 2 weeks of starting glucocorticoids
   • Long-segment specimen (>1 cm) recommended to reduce false negatives
   • Initially unilateral biopsy of the symptomatic side

3. If Temporal Artery Biopsy is Negative but Clinical Suspicion Remains High:

   • Proceed with noninvasive vascular imaging

4. Vascular Imaging Options:

   • MRI/MRA of cranial arteries
   • CT angiography
   • Vascular ultrasound (shows characteristic dark halo around temporal artery lumen in 73% of cases)
   • FDG-PET/CT in select cases

Important Considerations

• Timing: Biopsy should be performed within 2 weeks of starting glucocorticoids to minimize false negatives
• Skip Lesions: False negatives can occur due to "skip lesions" in the temporal artery
• Age Factor: Age ≥50 years has positive likelihood ratio for GCA diagnosis
• Laboratory Values: The diagnostic utility of ESR, CRP, and platelet values decreases after steroid initiation 3

Diagnostic Criteria

The American College of Rheumatology diagnostic criteria for GCA include:

• Age ≥50 years at disease onset
• New-onset or change in headache pattern
• Temporal artery abnormalities (thickening, tenderness, decreased pulse)
• Elevated ESR (>50 mm/h)
• Abnormal temporal artery biopsy showing vasculitis with mononuclear infiltrate and multinucleated giant cells

Pitfalls to Avoid

• Delayed Diagnosis: Can lead to permanent vision loss; start treatment immediately if high clinical suspicion
• Relying on Single Clinical Feature: No single clinical or laboratory feature is sufficient to rule in or rule out GCA 1
• Inadequate Biopsy: Short-segment biopsies increase false negative rates
• Mimicking Conditions: Temporal arteritis can be confused with angle-closure glaucoma, hypertension, migraine, trigeminal neuralgia, and other conditions

Remember that while European guidelines suggest diagnosis can be made with positive imaging tests alone, the American College of Rheumatology still recommends temporal artery biopsy as the diagnostic test of choice in the US due to limited expertise with temporal artery imaging techniques 1.