A 62-year-old Indian woman presents with a 6-week history of progressive headache, jaw claudication, and blurred vision in the left eye. On examination, she has temporal artery tenderness and reduced visual acuity (6/60 in the left eye). ESR is 78 mm/hr, and CRP is elevated. Fundoscopy shows optic disc pallor. What is the most likely diagnosis, and what is the primary pathological mechanism of vision loss in this condition?

Explanation

## Clinical Diagnosis: Giant Cell (Temporal) Arteritis **Key Point:** Giant cell arteritis (GCA) is a large-vessel vasculitis affecting the aorta and its branches, most commonly the temporal arteries. It is the most common vasculitis in patients >50 years and a medical emergency due to the risk of sudden vision loss. ## Diagnostic Criteria Met in This Case | Feature | Present | Significance | |---------|---------|---------------| | **Age >50 years** | Yes (62 F) | Essential criterion | | **Temporal artery tenderness** | Yes | Highly specific for GCA | | **Jaw claudication** | Yes | Claudication of muscles of mastication; pathognomonic | | **Vision loss (acute/subacute)** | Yes (6/60 left eye) | **EMERGENCY sign** | | **Elevated ESR/CRP** | Yes (78 mm/hr) | Acute phase response | | **Optic disc pallor** | Yes | Indicates ischemic damage | ## Pathophysiology of Vision Loss ### Anterior Ischemic Optic Neuropathy (AION) **High-Yield:** Vision loss in GCA occurs via **vasculitis of the posterior ciliary arteries** (branches of the ophthalmic artery, which is a branch of the internal carotid artery). This leads to: 1. **Inflammation and intimal thickening** of the posterior ciliary arteries 2. **Thrombosis** within these vessels 3. **Ischemia of the optic nerve head** (anterior optic nerve) 4. **Sudden, painless vision loss** with optic disc pallor and edema **Clinical Pearl:** The vision loss in GCA is typically **sudden and painless**, distinguishing it from the gradual vision loss in other conditions. Once vision is lost, it is often **irreversible** — hence the urgency of diagnosis and treatment. ### Histopathology of GCA ```mermaid flowchart TD A[Large-vessel vasculitis of elastic arteries]:::outcome A --> B[Granulomatous inflammation]:::action B --> C[Intimal proliferation and fibrosis]:::action C --> D[Luminal narrowing]:::outcome D --> E{Which vessel affected?}:::decision E -->|Temporal artery| F[Headache, jaw claudication]:::outcome E -->|Posterior ciliary artery| G[AION, vision loss]:::urgent E -->|Aorta/aortic branches| H[Aortic regurgitation, limb claudication]:::outcome G --> I[Optic disc pallor, edema]:::outcome ``` **Mnemonic for GCA Complications: "VISION"** - **V**ision loss (AION) — most feared complication - **I**nternal carotid/ophthalmic artery involvement - **S**udden, painless vision loss - **I**schemic optic neuropathy - **O**ptic disc pallor - **N**eeds urgent treatment (high-dose corticosteroids) ## Why Anterior Ischemic Optic Neuropathy? The posterior ciliary arteries supply the optic nerve head. Vasculitis of these arteries causes: - **Segmental ischemia** of the optic nerve - **Non-arteritic AION** (in this case, arteritic AION due to GCA) - **Sudden vision loss** with optic disc pallor - **Permanent visual deficit** if untreated **Warning:** Do NOT confuse with: - ~~Amaurosis fugax~~ (transient vision loss from carotid atherosclerosis) - ~~Retrobulbar optic neuritis~~ (demyelination; usually younger patients, pain on eye movement) - ~~Central retinal artery occlusion~~ (cherry-red spot on fundoscopy, not optic disc pallor) ## Management Implications 1. **Temporal artery biopsy** — shows granulomatous inflammation with giant cells (diagnostic gold standard) 2. **Immediate high-dose corticosteroids** — 40–60 mg prednisone daily to prevent further vision loss 3. **ESR/CRP monitoring** — to assess treatment response 4. **Ophthalmology referral** — urgent evaluation of vision and risk of fellow eye involvement [cite:Robbins 10e Ch 11; Harrison 21e Ch 378]