A 62-year-old woman with a 6-month history of headache, jaw claudication, and visual disturbances (amaurosis fugax) is suspected to have giant cell (temporal) arteritis. Which investigation is the most appropriate next step to confirm the diagnosis?

Explanation

## Diagnosis of Giant Cell Arteritis ### Gold Standard Confirmatory Test **Key Point:** Temporal artery biopsy (TAB) is the gold standard for confirming giant cell arteritis (GCA). It demonstrates granulomatous inflammation with giant cells and intimal proliferation in the temporal artery. ### Histopathological Findings on TAB **High-Yield:** Classic features include: - Granulomatous inflammation (epithelioid histiocytes, lymphocytes) - Giant cells (often multinucleated) - Intimal proliferation and media necrosis - Fragmentation of the internal elastic lamina - Skip lesions (patchy involvement) ### Sensitivity and Timing | Aspect | Detail | | --- | --- | | Sensitivity | 80–90% (higher if multiple sections examined) | | Specificity | >95% | | Optimal timing | Within 1–2 weeks of symptom onset; sensitivity decreases after 4 weeks | | Biopsy length | Minimum 1 cm; longer specimens improve diagnostic yield | | Skip lesions | Present in ~10% of cases; bilateral biopsy may be considered if high suspicion | ### Clinical Pearl **Clinical Pearl:** Do NOT delay corticosteroid therapy while awaiting biopsy in suspected GCA with vision-threatening symptoms. Start high-dose prednisone (40–60 mg/day) immediately if clinical suspicion is high; biopsy can be performed within 1–2 weeks without significantly affecting histology. ### Diagnostic Approach ```mermaid flowchart TD A[Clinical suspicion: age >50, headache, jaw claudication, visual symptoms]:::outcome A --> B[Check ESR/CRP]:::action B --> C{ESR elevated or CRP positive?}:::decision C -->|Yes| D[Start corticosteroids if vision threat]:::action C -->|No| E[GCA unlikely; consider alternatives]:::outcome D --> F[Temporal artery biopsy within 1-2 weeks]:::action F --> G{Granulomatous inflammation + giant cells?}:::decision G -->|Yes| H[GCA confirmed]:::outcome G -->|No| I[Reconsider diagnosis]:::outcome ``` ### Why Other Options Are Suboptimal **Doppler ultrasound:** Non-invasive and increasingly used as a screening tool (halo sign, compression sign), but is operator-dependent and not a gold standard. Cannot replace biopsy for definitive diagnosis. **PET scan:** Useful for detecting large-vessel involvement (aortitis) in GCA, but is not the primary confirmatory test for cranial GCA and is expensive. **Serum IL-6 level:** Elevated in GCA but non-specific; not used for diagnosis. IL-6 may help monitor disease activity but does not confirm GCA.