## Diagnosis of Giant Cell Arteritis (GCA) ### Gold Standard Investigation **Key Point:** Temporal artery biopsy remains the gold standard and most specific confirmatory test for giant cell arteritis, demonstrating granulomatous inflammation with giant cells and intimal proliferation in the arterial wall. ### Histopathological Findings on Biopsy 1. **Granulomatous inflammation** — epithelioid histiocytes and lymphocytes 2. **Giant cells** — multinucleated cells at the media-intima junction 3. **Intimal proliferation** — leading to luminal narrowing 4. **Preserved elastic lamina** — distinguishes from atherosclerosis ### Why Biopsy is Essential **Clinical Pearl:** ESR and CRP are sensitive but not specific for GCA; they can be elevated in many conditions. Biopsy provides definitive tissue diagnosis and guides long-term corticosteroid therapy decisions. **High-Yield:** A negative biopsy does not exclude GCA if clinical suspicion remains high (sensitivity ~90%), but a positive biopsy is diagnostic. Bilateral temporal artery sampling increases diagnostic yield. ### Biopsy Timing **Warning:** Biopsy should be performed within 1–2 weeks of symptom onset; delayed biopsy (>4 weeks) may show fibrosis without active inflammation, reducing sensitivity. Corticosteroid therapy can be initiated while awaiting biopsy results if clinical suspicion is very high and vision-threatening symptoms are present. ### Table: Investigations in GCA | Investigation | Sensitivity | Specificity | Role | | --- | --- | --- | --- | | ESR/CRP | High | Low | Screening, disease activity | | Temporal artery biopsy | ~90% | >95% | **Gold standard diagnosis** | | Doppler ultrasound | ~80% | ~95% | Non-invasive, operator-dependent | | CT/MR angiography | Moderate | Moderate | Assess large vessel involvement | **Mnemonic: GCA Diagnosis = **B**iopsy (Gold standard), **E**SR/CRP (screening), **S**ymptoms (clinical) — **BES** confirms GCA. 
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