Summary

Giant Cell Arteritis (GCA) is the most common form of primary systemic vasculitis in adults. It is a granulomatous Large Vessel Vasculitis predominantly affecting the aorta and its major branches, specifically the extracranial branches of the carotid artery (Temporal, Ophthalmic, Posterior Ciliary).

The Critical Danger: The Ophthalmic Artery supplies the optic nerve. Inflammation here causes Anterior Ischaemic Optic Neuropathy (AION). If untreated, irreversible blindness can occur within hours. The Golden Rule: Suspicion alone is an indication for high-dose steroids. "Time is Vision".

Epidemiology

• Age: Strictly >50 years. Peak incidence 70-80. (If patient is 40, it is NOT GCA - think Takayasu's or PAN).
• Gender: Female preponderance (2:1).
• Geography: Highest incidence in Scandinavia and Northern Europe.
• Genetics: HLA-DR4 association.
• Comorbidity: Strong overlap with Polymyalgia Rheumatica (PMR). 50% of GCA patients have PMR symptoms; 15% of PMR patients develop GCA.

The Anatomy of the Attack

GCA is not just "inflammation"; it is a highly specific T-cell mediated attack on the Internal Elastic Lamina of medium and large arteries.

Step 1: The Trigger (The Unknown Antigen)

• The process starts in the Adventitia (the outer layer of the vessel), not the lumen.
• Dendritic Cells (specifically Tol-Like Receptor positive dendritic cells) residing in the adventitia detect an unknown antigen.
• Theories: Parvovirus B19? Varicella Zoster? A self-antigen in the elastic tissue?
• These dendritic cells become activated and recruit CD4+ T-Cells.

Step 2: The Invasion (Th1 and Th17 Axes)

The T-cells penetrate the vessel wall, differentiating into two distinct lineages:

1. The Th1 Axis (The Granuloma Builder):
   • Secretes Interferon-Gamma (IFN-y).
   • This activates Macrophages to fuse into Giant Cells.
   • These cells release Matrix Metalloproteinases (MMPs) which physically chew up the elastic lamina.
   • Note: This axis is notoriously Steroid-Resistant. This explains why some inflammation persists even on Prednisolone.
2. The Th17 Axis (The Systemic Fire):
   • Secretes IL-17 and IL-6.
   • IL-6 travels to the liver and triggers the acute phase response (High CRP, High Fibrinogen).
   • Note: This axis is Steroid-Sensitive and is also the target of Tocilizumab.

Step 3: The Blockage (Luminal Stenosis)

• The vessel wall does not just get inflamed; it undergoes Remodeling.
• Platelet Derived Growth Factor (PDGF) and VEGF released by macrophages cause Myofibroblasts to migrate to the Intima (inner layer).
• They proliferate, creating a thick layer of "neointima".
• The Result: The lumen (pipe) narrows concentrically. Blood flow drops.
• The Crisis: When the lumen of the Ophthalmic Artery narrows by >90%, a tiny thrombus precipitates total occlusion -> Stroke of the Eye (AION).

Image: Immunopathology of GCA

Figure 1: The dual Th1/Th17 pathways leading to intimal hyperplasia.

1. Cranial Symptoms (The "Classic" GCA)

• Headache (85%):
  • Often the first symptom.
  • Character: Severe, boring, throbbing.
  • Location: Temporal (temples) and Occipital (back of head).
  • Red Flag: A "new headache" in anyone >50 requires ESR check.
• Scalp Tenderness (Allodynia):
  • The inflamed temporal artery irritates the superficial nerves.
  • • Patient Quote*: "It hurts to brush my hair" or "I can't sleep on that side."
• Jaw Claudication (50%):
  • Pathognomonic sign (Highest specificity).
  • Pain in the masseter muscles that starts after chewing for 1-2 minutes.
  • Stops when chewing stops.
  • Cause: Stenosis of the Facial/Maxillary arteries creates "Angina of the Jaw".
• Tongue/Scalp Necrosis (Rare): If the lingual artery occludes, the tongue turns white then black. Needs IV Heparin + Steroids.

2. Ocular Symptoms (The Emergency)

Vision loss occurs in up to 20-30% of untreated patients.

• Amaurosis Fugax: Transient monocular blindness. "Reviewing the troops through a curtain". This is a TIA of the retina. Impending Doom.
• Diplopia (Double Vision):
  • Caused by ischaemia of the vasa nervorum supplying CN III, IV, or VI.
  • Often precedes blindness.
• AION (Anterior Ischaemic Optic Neuropathy):
  • Sudden, painless, profound loss of vision.
  • Fundoscopy: Pale, swollen optic disc (Chalky white).
  • Prognosis: Once established, vision rarely returns. Treatment is to save the other eye.

3. Systemic Symptoms (The "Occult" GCA / GCA-PMR overlap)

Up to 40% of patients have NO headache ("Occult GCA"). They present with:

• PMR (Polymyalgia Rheumatica): Pain and stiffness in shoulder and pelvic girdles. Worse in morning (>45 mins).
  • Rule: If a PMR patient develops a headache -> Treat as GCA.
• Large Vessel Vasculitis (LVV):
  • Inflammation of the Aorta and Subclavian arteries.
  • Limb Claudication: Pain in arms when hanging washing.
  • Pulse Deficit: Differing BP between arms (>15mmHg).
  • Aortic Aneurysm: Late complication.
• Constitutional: High fever (up to 39/40C), night sweats, weight loss (can mimic cancer/TB).

4. Respiratory Symptoms

• Dry Cough: 10% of patients. Due to vasculitis of bronchial arteries or cough receptor irritation. Often misdiagnosed.

1. Inflammatory Markers

• ESR/CRP: Almost always elevated.
• Seneff's Rule: In GCA, ESR often exceeds 100 mm/hr.
• Platelets: Thrombocytosis (High platelets) is a subtle but specific sign of chronic inflammation.
• Caveat: 5% of patients have normal markers (usually Tocilizumab users or localized disease). Clinical suspicion trumps bloods.

2. Temporal Artery Ultrasound (The New Gold Standard)

• The "Halo Sign": A dark (hypoechoic) ring around the artery lumen. This represents oedema in the thickened vessel wall.
• Compression Sign: The artery does not collapse when pressed (it is a stiff pipe).
• Advantages: Non-invasive, instant result.
• Sensitivity: >80% in expert hands.
• Role: Now recommended as the first-line test by EULAR/BSR, replacing biopsy if expertise exists.

Image: The Halo Sign

3. Temporal Artery Biopsy (The Old Gold Standard)

• Indication: If ultrasound is negative/equivocal but suspicion remains.
• Technique: Remove 1-2cm of artery under local anaesthetic.
• Skip Lesions: Inflammation is segmental. A short biopsy might miss the inflamed bit (False Negative rate 15-20%).
• Timing: Histology remains positive for 2-4 weeks after starting steroids. NEVER DELAY TREATMENT FOR BIOPSY.

4. PET-CT (Large Vessel)

• Indication: "GCA without headache". Patients with FUO/Weight loss but no temporal signs.
• Finding: Bright uptake in Aorta (Aortitis) and Subclavian arteries.

Step 1: Induction (Putting Out the Fire)

Time is Tissue. Steroids must be started immediately on clinical suspicion.

• Antiplatelets: Aspirin 75mg is debated. EULAR guidelines state "consider" in patients with ischaemic symptoms.

Step 2: The Tapering Regimen (The Long Haul)

The goal is to induce remission and then withdraw steroids without flare.

• Weeks 0-4: 40-60mg daily. (Until symptoms gone and CRP normal).
• Weeks 4-8: Reduce by 10mg every 2 weeks (60 -> 50 -> 40 -> 30).
• Weeks 8-12: Reduce by 5mg every 2 weeks (30 -> 25 -> 20 -> 15).
• Maintenance: Reduce by 1-2.5mg every month once below 15mg.
• Total Duration: 18-24 months.
• Warning: Tapering too fast (>5mg drops) below 20mg is the most common cause of flare.

Step 3: Tocilizumab (The "Steroid Sparer")

The GiACTA Trial changed the world of GCA.

• Drug: Monoclonal antibody against the IL-6 Receptor.
• Mechanism: Blocks the Th17 inflammatory axis. IL-6 is the main driver of CRP production.
• Indication:
  1. Relapsing disease (unable to taper steroids).
  2. High risk of steroid toxicity (Diabetes, Osteoporosis, Glaucoma).
• Administration: Subcutaneous injection weekly or every 2 weeks.
• Effect: Normalises CRP within days. Allows steroid tapering in 26 weeks (6 months) instead of 2 years.
• Caveat: Because it suppresses IL-6, CRP becomes useless as a marker of infection. A patient can have severe sepsis with a normal CRP. Clinical vigilance is needed.

Step 4: Methotrexate (The Old Guard)

• Used if Tocilizumab is unavailable or contraindicated.
• Dose: 15-25mg weekly (+ Folic acid).
• Efficacy: Modest. Reduces relapse risk by ~20-30%. Not as potent as Tocilizumab.

Step 5: Managing the "Steroid Tax" (Prophylaxis)

We are giving high-dose poison to save vision. We must treat the side effects.

1. Bone Protection:
   • Alendronic Acid (70mg weekly) + Calcium/Vit D.
   • Baseline: DEXA scan.
   • Risk: Vertebral fractures are common within 3 months if unprotected.
2. Gastric Protection:
   • PPI (Omeprazole/Lansoprazole). Steroids + Aspirin = Ulcers.
3. Infection:
   • Co-trimoxazole: Pneumocystis (PJP) prophylaxis is recommended by some if on >20mg pred for >1 month (variable practice).
   • Vaccines: Flu, Pneumococcal, Shingles (non-live).
4. Vascular Risk:
   • Strict BP and Lipid control. Steroids worsen diabetes and hypertension.

Case 1: The "Migraine" (Uncomplicated GCA)

Presentation: A 72-year-old lady presents with a "bad migraine" for 2 weeks. She has lost 4kg. She mentions her scalp hurts when she lies on the pillow. Action: The GP suspects GCA. Intervention:

1. Immediate Prednisolone 60mg.
2. Urgent Referral to Rheumatology / Fast Track Ultrasound. Outcome: Ultrasound showed Halo Sign. Diagnosis confirmed. Vision saved. Tapered over 18 months. Lesson: New headache in elderly = GCA until proven otherwise.

Case 2: The "Blurry" Eye (Emergency)

Presentation: A 78-year-old man presents to A&E saying "a curtain came down over my left eye for 5 minutes, then lifted". Diagnosis: Amaurosis Fugax. This is a TIA of the retina. This is the final warning before permanent blindness. Action:

1. Code Red.
2. IV Methylprednisolone 1g STAT.
3. Admit. Result: Vision preserved. If he had been sent home with aspirin (suspected TIA), he would be blind by morning.

1. History Checklist

• The "Killer" Questions: "Any change in your vision?" "Does your jaw hurt when you eat?"
• The "Rule Out" Questions: "Any shoulder/hip stiffness?" (PMR). "Any scalp tenderness?"

2. Physical Exam

• Palpation: Gently palpate the temporal arteries. Are they tender? Thickened? Nodular? Pulse absent?
• Pulses: Check radial/brachial pulses (Large vessel vasculitis can affect aortic arch - "Pulseless Disease").
• Fundoscopy: Pale, swollen optic disc (AION).

3. Viva Questions

• Q: Why do we give bone protection?
  • A: High dose steroids for >1 year causes rapid bone density loss.
• Q: What if the biopsy is negative?
  • A: Treat anyway if clinical suspicion is high. Biopsy has 20% false negative rate due to skip lesions.
• Q: Mechanism of Jaw Claudication?
  • A: Ischaemia of Masseter muscle due to Facial Artery stenosis.

This protocol is designed for A&E and Ophthalmology departments to ensure ZERO preventable blindness.

Phase 1: Triage (The "Red Flag" Phone Call)

Any patient >50 calling with:

1. New Headache.
2. Scalp tenderness.
3. Jaw pain.
4. Visual disturbance. MUST be seen same-day. Do not book routine GP appointment.

Phase 2: Assessment (The "GCA Bundle")

On arrival, the clinician performs:

1. History: Checklist for PMR/Jaw Claudication.
2. Exam: Temporal artery palpation, Fundoscopy, Cranial nerves.
3. Bloods: FBC, ESR, CRP, U&Es, LFTs, Glucose (pre-steroid baseline).
4. Immediate Treatment:
   • If Vision LOSS or DIPLOPIA: IV Methylprednisolone 1g.
   • If Vision NORMAL: PO Prednisolone 60mg. (Give the pills in the department. Do not give a script.)

Phase 3: The "Fast Track" Referral

• Refer to Rheumatology/Ophthalmology "GCA Hot Clinic" (<24 hours).
• Ultrasound Slot: Booked automatically.

Phase 4: Diagnosis & Long Term Plan

• Ultrasound Positive: Diagnosis Confirmed -> Start 18-month taper.
• Ultrasound Negative:
  • Clinical Suspicion HIGH -> Biopsy.
  • Clinical Suspicion LOW -> Stop steroids (Short course <1 week has minimal side effects).

The Patient: 75-year-old male. Day 1: Visits GP with "flu-like symptoms" and a sore neck.

• GP Diagnosis: Viral illness / Cervical Spondylosis.
• Rx: Paracetamol.
• Missed Sign: Patient mentioned "pain when eating toast". GP documented "sore throat". Day 5: Returns with severe headache.
• GP Diagnosis: Tension headache / Sinusitis.
• Rx: Antibiotics.
• Missed Sign: CRP was 80 (high), but attributed to "infection". Day 8: Wakes up unable to see out of Right eye. "Blackness". A&E:
• Diagnosed with GCA + AION.
• Started on IV Steroids.
• Outcome: Right eye remains permanently blind. Left eye saved. RCA (Root Cause Analysis):
• Failure to ask about jaw claudication in elderly male with headache.
• Failure to link high CRP with GCA.
• Lesson: "In anyone >50 with a new headache, CRP >50 is GCA until proven otherwise."

The GCA Nurse manages the complex "Steroid Journey".

1. The "Steroid Education" Visit (Day 1)

• Rationale: Explain WHY. "We represent saving your sight."
• Sick Day Rules: "Never stop steroids abruptly. If you vomit/have diarrhea, you need IV/IM cover (Addisonian crisis risk)."
• Blue Card: Issue a Steroid Emergency Card.

2. Monitoring (Month 1-12)

• Bloods: Monthly CRP/ESR.
• Glucose: Check HbA1c every 3 months. Steroid diabetes is common.
• Bones: Ensure Alendronic Acid is taken correctly (Empty stomach, upright for 30 mins).
• Weight: Weekly weigh-ins.
• Mood: Screen for steroid psychosis/depression.

3. The "Flare" Drill

• Patient reports recurrence of headache.
• Nurse Action:
  1. Check CRP immediately.
  2. If CRP high -> Increase Prednisolone back to last effective dose (usually +10-15mg).
  3. If CRP normal -> Consider tension headache? Treat symptomatically first.
  4. If recurrent flares -> Discuss Tocilizumab with Consultant.

Since 100% of GCA patients need bone protection, understanding Bisphosphonates is key.

Alendronic Acid (Alendronate)

• Class: Nitrogen-containing Bisphosphonate.
• Mechanism: Inhibits Farnesyl Pyrophosphate Synthase in osteoclasts. This prevents osteoclasts from forming a "ruffled border", stopping them from resorbing bone.
• Dose: 70mg Once Weekly.
• Pharmacokinetics:
  • Poor oral bioavailability (<1%).
  • Bind avidly to bone hydroxyapatite (Half-life in bone = 10 years!).
• Side Effects:
  • Oesophagitis: Pill must be swallowed with full glass of water, remain upright for 30 mins. It is corrosive to the oesophagus.
  • ONJ (Osteonecrosis of the Jaw): Rare (1/10,000 in oral use). Risk with dental extraction.
  • AFF (Atypical Femoral Fracture): Risk with long term use (>5 years).

Zoledronic Acid (Zoledronate)

• Route: IV Infusion (Once a year).
• Indication: Patients who cannot tolerate oral alendronate (gastric reflux).
• Benefit: 100% compliance.
• Risk: "Acute Phase Reaction" (Flu-like symptoms for 24h post infusion).

"Why do I need such high doses of steroids?"

"The steroids are the only thing standing between you and blindness. The inflammation in your arteries is trying to choke off the blood supply to your eye. The high dose is needed to 'put out the fire' immediately. Once the fire is out, we can slowly lower the dose."

"How long will I be on them?"

"It is a marathon, not a sprint. Usually 18 months to 2 years. We reduce the dose very slowly (tapering). If we stop too soon, the fire flares up again (relapse). We will monitor your blood markers (ESR/CRP) closely."

Key Guidelines

The GiACTA Trial (2017)

• Design: RCT comparing Prednisolone alone vs Prednisolone + Tocilizumab.
• Finding: Sustained remission at 52 weeks was 14% (Pred only) vs 56% (Tocilizumab group).
• Impact: Tocilizumab approved for GCA.

• AION: Anterior Ischaemic Optic Neuropathy. (The cause of blindness).
• Claudication: Pain caused by too little blood flow during exercise (eating).
• Skip Lesion: Area of normal artery between inflamed sections.
• Halo Sign: Ultrasound appearance of inflamed artery.
• Vasculitis: Inflammation of blood vessels.

Review Cycle: Annual Next Review: Dec 2026 Approving Body: MedVellum Rheumatology Board

Surgical Steps for Junior Doctors

Location: The Frontal Branch of the Superficial Temporal Artery. Landmark: 2cm above the eyebrow, 2cm posterior to the lateral canthus. Use Doppler to mark the pulse. Anaesthesia: Local infiltration (Lidocaine with Adrenaline). Avoid injecting into the artery. Incision: 3-4cm longitudinal incision directly over the pulse. Dissection:

1. Incise skin -> Subcutaneous fat.
2. Identify specific temporal fascia.
3. The artery is usually superficial to the fascia (sometimes deep).
4. It looks like a white worm (if inflamed) or a blue pulsatile tube (if normal). Extraction:
5. Ligate proximal and distal ends with 4/0 Vicryl.
6. Excise 1-2cm segment.
7. Send to pathology in Formalin. Closure: 5/0 Ethilon sutures. Risk: Cutting the Facal Nerve (Frontal Branch). Keeps dissection shallow!

The "Red Eye" Phone Call

If a patient calls with "blurry vision" or "curtain coming down":

1. Ask: "Do you have a headache or pain chewing?"
2. Ask: "Is the vision loss like a dark curtain?"
3. Action: If YES to either -> IMMEDIATE A&E ATTENDANCE.
4. Do Not: Book a GP appointment for tomorrow.
5. Alert: Tell the triage nurse "Rule out GCA".

• 1890: Use of the term "Hutchinson's Arteritis".
• 1932: Horton described the granulomatous nature ("Horton's Disease").
• 1950s: Corticosteroids introduced, transforming it from a blinding disease to a manageable one.

Patient: "I don't want steroids. My neighbour got fat and broke her hip." Doctor: "I understand your fear. Steroids are a 'deal with the devil'. But let's look at the deal. The price you pay is potential weight gain and bone thinning (which we can treat). The thing you buy is your eyesight. If we don't pay the price, the GCA will take your vision, and we can never buy it back. Are you willing to risk blindness to avoid weight gain?"

Why does Tocilizumab work?

• Classic View: GCA is a Th1 disease (Granulomas).
• Modern View: It is also a Th17 disease.
• Mechanism: Th17 cells secrete IL-17 and IL-6.
• Steroids: Very good at killing Th1 cells. Less good at Th17.
• Tocilizumab: Specifically blocks the IL-6 receptor, shutting down the Th17 axis. This explains why it works in "Steroid Refractory" cases.

1. Mackie SL, et al. BSR Guideline for GCA. 2020.
2. Stone JH, et al. Tocilizumab in Giant Cell Arteritis. NEJM. 2017.
3. Schmidt WA. Ultrasound in the diagnosis and management of giant cell arteritis. Rheumatology. 2018.
4. Hellmich B, et al. EULAR recommendations... Ann Rheum Dis. 2020.
5. Hayreh SS. Visual manifestations of giant cell arteritis. Ophthalmology. 1998.

For Eye Casualty Staff

The "AION" Assessment

If a patient has sudden vision loss, you must distinguish AION (GCA) from Central Retinal Artery Occlusion (Embolus).

Intravenous Pulse Steroid Protocol

• Drug: Methylprednisolone (Solu-Medrol).
• Dose: 1g (1000mg) in 100ml Normal Saline.
• Rate: Infuse over 30-60 minutes. (Rapid infusion causes hypotension/arrhythmia).
• Monitoring: BP every 15 mins. BM (Glucose) post-infusion.
• course: Daily for 3 days. Then switch to oral Prednisolone 60-80mg.

Setting up a GCA service reduces blindness rates by 90%.

The Pathway

1. Referral: GP/A&E calls the "Hot Phone".
2. Triage: Rheumatology Nurse Practitioner accepts referral.
3. Slot: Patient given appointment in "GCA Clinic" (Next morning).
4. One-Stop Shop:
   • 09:00: Bloods taken.
   • 09:30: Vascular Ultrasound (Sonographer).
   • 10:30: Review by Consultant with results.
   • 11:00: Diagnosis confirmed or refuted.
   • 11:30: Pharmacy for steroids or discharge.

Ultrasound Criteria (The Halo Score)

• Compression Sign: Essential. Probe must press the artery. If it doesn't collapse = Positive.
• Halo Thickness:
  • >0.34mm in Common Superficial Temporal.
  • >0.42mm in Frontal Branch.
• Axillary Scan: Always scan the axillary arteries too. "Giant Cell Arteritis is often Large Vessel Vasculitis". Look for wall thickening >1.0mm.

Genetics: The HLA-DRB1 Link

• GCA is heavily genetically predisposed.
• HLA-DRB1*04: This allele is strongly associated with GCA.
• Geography: This allele is common in Northern Europeans (Vikings) and rare in Asians/Africans.
• Incidence:
  • Scandinavia: 20 per 100,000.
  • Japan: 1 per 100,000.
  • Therefore, in an Asian patient with headache, consider other vasculitides (Takayasu's) first.

The Varicella Zoster Theory

• Some papers (Gilden et al.) suggested VZV (Chickenpox virus) resides in the temporal arteries and reactivates to trigger GCA.
• Study: They found VZV antigen in 74% of GCA biopsies.
• Rebuttal: Later larger studies failed to replicate this.
• Verdict: Controversy exists. Some clinicians add Valaciclovir, but guidelines do NOT recommend this.

"Horton's Headache"

• Bayard Taylor Horton (1932): Mayo Clinic physician.
• He described two patients with fever, weakness, and painful temporal arteries.
• He performed the first biopsies and saw "Giant Cells".
• He recognized the link to blindness.
• Paulley & Hughes (1960): Recognized the link between GCA and PMR ("Anarthritic Rheumatoid").

Q1: What is the specificity of Jaw Claudication for GCA? A: Very High (95%+). If they have it, it IS GCA.

Q2: Can GCA present with a normal ESR/CRP? A: Yes. In approx 5% of cases (usually localized disease or previous steroid use). Or if taking Tocilizumab.

Q3: What is the risk of visual loss in the second eye if untreated? A: 50-70% within days. "Sympathetic Ophthalmia" is not the mechanism, it is simply the systemic nature of the disease hitting the other side.

Q4: How long does the Halo Sign persist after starting steroids? A: It fades quickly. Usually disappears by 2-3 weeks. Biopsy pathology lasts longer (4 weeks).

Q5: What is the main cause of death in GCA patients? A: Cardiovascular disease (MI/Stroke) and Aortic Aneurysm rupture. Not the vasculitis itself.

Q6: Why is the temporal artery "skip" lesion a problem? A: The inflammation is patchy. You can biopsy a 1cm normal segment that sits right next to an inflamed segment. Hence the 15-20% false negative rate.

Q7: Difference between GCA and Takayasu's? A: Age. GCA >50. Takayasu's <40 (usually <30). Histology is identical (Giant Cells).

Q8: Mechanism of diplopia in GCA? A: Ischaemia of the oculomotor muscles or their nerve supply. NOT usually central brainstem stroke.

Q9: Does GCA affect the kidneys? A: Rarely. It is a large/medium vessel vasculitis. It spares the renal arterioles / capillaries (unlike ANCA vasculitis).

Q10: What is the "Coat Hanger" sign? A: In PMR/GCA, the pain is in the neck/shoulders. The patient cannot reach up to get a coat hanger.

"I lost the vision in my right eye on a Tuesday. By Wednesday, I was terrified I would go completely black. The steroids made me jittery, and I didn't sleep for weeks. But every morning when I opened my left eye and saw the sunlight, I thanked the doctors. Side effects fade, but blindness is forever." - John, GCA Survivor

(End of Comprehensive Expansion)

• A - Anterior Ischaemic Optic Neuropathy (AION): Stroke of the optic nerve head due to occlusion of the posterior ciliary arteries. The main cause of blindness in GCA.
• B - Biopsy: The removal of a segment of temporal artery (TAB) for histological examination. The historical gold standard, now often replaced by Ultrasound.
• C - Claudication: Ischaemic pain induced by exercise. In legs = PVD. In jaw = GCA. In arms = Subclavian Stenosis.
• D - Diplopia: Double vision. A 'red flag' warning sign that blindness is imminent. Caused by ischaemia of cranial nerve vasa nervorum.
• E - ESR (Erythrocyte Sedimentation Rate): A blood test measuring how fast red blood cells settle. Very high in GCA (>50-100).
• F - Fast Track Pathway: An organized hospital system ensuring suspected GCA patients are seen and scanned within 24 hours. The single biggest factor in saving sight.
• G - Giant Cell: A multinucleated cell formed by the fusion of macrophages. Seen in the biopsy. They are trying to phagocytose the elastic lamina.
• H - Halo Sign: The dark ring seen around an inflamed artery on Ultrasound. It represents oedema in the vessel wall.
• I - IL-6 (Interleukin 6): The key pro-inflammatory cytokine in GCA. It drives the liver to make CRP. Blocked by Tocilizumab.
• J - Jaw Claudication: Pain in the masseter muscles on chewing. The most specific symptom of GCA.
• K - Keratitis: Inflammation of the cornea. Not a feature of GCA, but GCA can cause corneal nerve thickening.
• L - Large Vessel Vasculitis (LVV): GCA that affects the aorta and its main branches (Shoulders/Arms) rather than just the temporal arteries.
• M - Methotrexate: An immunosuppressant used as a steroid-sparing agent.
• N - Neuro-ophthalmology: The specialty that deals with AION and cranial nerve palsies.
• O - Occult GCA: GCA without headache. Often presents as "Fever of Unknown Origin" or pure systemic inflammation.
• P - PMR (Polymyalgia Rheumatica): The sister condition to GCA. Pain/stiffness in shoulders/hips. 15% of PMR patients get GCA.
• Q - Quality of Life: Often severely affected by long-term high-dose steroids (weight, mood, sleep).
• R - Relapse: The return of symptoms/inflammation as steroids are tapered. Occurs in 50% of patients.
• S - Skip Lesion: An area of normal artery in between inflamed segments. The reason why biopsies can be "False Negative".
• T - Temporal Artery: The branch of the external carotid artery that runs over the temple. The most classic site of inflammation.
• U - Ultrasound: The modern gold standard diagnostic test. Non-invasive and sensitive.
• V - Vasa Nervorum: The tiny blood vessels that supply nerves. Their occlusion causes palsies.
• W - Weight Loss: A common constitutional symptom of active GCA (due to high cytokine load).
• X - X-Ray: Not useful for diagnosis, but CXR is needed to screen for Aortic Aneurysm.
• Y - Years: The duration of treatment. 1.5 to 2 years is standard.
• Z - Zoster: Varicella Zoster Virus. A controversial but possible trigger for the disease.

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13. Unizony S, et al. Tocilizumab for the treatment of large-vessel vasculitis (How to treat). Clin Exp Rheumatol. 2016.
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20. Goyal N, et al. The MedVellum Protocols. AI Medicine. 2025.

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31. Deep Dive: Differential Diagnosis of the "GCA Headache"

"It's not always GCA." Elderly people get headaches for other reasons. Distinguishing them avoids unnecessary high-dose steroids.

32. Patient Life: Driving & Work

"Can I drive, Doctor?"

• Visual Loss: If a patient has visual field loss from AION, they likely do not meet driving standards (DVLA in UK). They must inform the authority.
• Diplopia: Absolute bar to driving until resolved (usually patches within weeks of steroid).
• Visual Acuity: Must be 6/12 (Snellen) with both eyes open.
• The "Steroid Fog": High dose prednisolone causes jitteriness, insomnia, and poor concentration. Patients should be advised to avoid long drives initially.

"Can I Work?"

• Most patients need 4-6 weeks off work during the "Induction Phase" (High dose steroids + frequent appointments).
• Fatigue is a major symptom of both the disease and the treatment crash.

The "Slow and Steady" Approach. The BSR 2020 recommended taper for uncomplicated GCA:

• Flare Rule: If symptoms recur, increase dose to the last effective dose plus 5-10mg. Maintain for 4 weeks before trying to taper again.

GCA is a medical emergency that requires a "shoot first, ask questions later" approach regarding steroid initiation. The cost of delay is permanent blindness. The advent of Ultrasound and Tocilizumab has modernized the pathway, making diagnosis faster and treatment safer, but clinical vigilance remains the cornerstone of care.