Giant Cell Arteritis

Detailed Overview

GCA is a medical emergency because inflammation and subsequent intimal hyperplasia of the ophthalmic artery can cause sudden, irreversible, painless vision loss (anterior ischemic optic neuropathy). It almost exclusively affects individuals over the age of 50. It is highly associated with Polymyalgia Rheumatica (PMR); about half of patients with GCA have PMR. Prompt administration of high-dose corticosteroids is mandatory even before diagnostic confirmation to prevent blindness.

Epidemiology & Demographics

Exclusively occurs in adults >50 years old, peaking in the 70s. It is most common in individuals of Northern European descent (Scandinavia) and affects women 2 to 3 times more often than men.

Etiological Mechanism

The exact cause is unknown, but it is considered an autoimmune disease triggered by an unknown antigen, possibly a virus (e.g., Varicella-Zoster), in genetically susceptible individuals (HLA-DRB1*04 alleles).

Primary Causes

Autoimmune/Idiopathic

Genetic Susceptibility (HLA-DR4)

• Age over 50: Disease virtually never occurs in younger individuals.
• Northern European Ancestry: Highest prevalence globally.
• Polymyalgia Rheumatica: Presence of PMR significantly increases the likelihood of developing GCA.

Dendritic cells in the adventitia of the vessel wall become activated and recruit CD4+ T-cells. These T-cells release interferon-gamma, which activates macrophages. Macrophages form multinucleated giant cells and release pro-inflammatory cytokines (IL-6, TNF-alpha) and metalloproteinases. This inflammatory cascade causes destruction of the internal elastic lamina. Healing responses trigger myofibroblast proliferation in the intima, causing massive intimal thickening. This narrows the arterial lumen, leading to downstream tissue ischemia (e.g., the optic nerve or masseter muscle).

Characteristic Clinical Presentation

• New Onset Headache: Typically unilateral, severe, throbbing pain localized to the temporal or occipital region.
• Jaw Claudication: Pain or fatigue in the jaw muscles that worsens with chewing food; highly specific for GCA.
• Visual Disturbances: Amaurosis fugax (transient vision loss), diplopia, or sudden permanent unilateral blindness.
• Systemic Symptoms: Fever, profound fatigue, and unintentional weight loss.

Physical Examination Signs

• Enlarged, nodular, and tender superficial temporal artery.
• Decreased or absent pulse in the temporal artery.
• Relative Afferent Pupillary Defect (Marcus Gunn pupil) if ischemic optic neuropathy has occurred.
• Scalp tenderness (pain upon combing hair).

• Irreversible Blindness: Anterior Ischemic Optic Neuropathy (AION); occurs in up to 20% of untreated patients.
• Aortic Aneurysm/Dissection: Inflammation of the aorta can lead to aneurysm formation, typically years after initial diagnosis.
• Stroke: Due to involvement of the carotid or vertebrobasilar arteries.

Diagnostic Criteria & Guidelines

Diagnosis relies on clinical suspicion supported by markedly elevated acute phase reactants. The gold standard is a Temporal Artery Biopsy showing transmural inflammation with mononuclear cells and multinucleated giant cells. Biopsy should be at least 1-2 cm long due to 'skip lesions'. Treatment MUST NOT be delayed to wait for the biopsy.

Differential Diagnosis

• Tension or Migraine Headache
• Trigeminal Neuralgia
• Non-arteritic Anterior Ischemic Optic Neuropathy (NAION)
• Takayasu Arteritis (occurs in younger patients)

Laboratory Tests & Biomarkers

• Erythrocyte Sedimentation Rate (ESR): Typically > 50 mm/h, often > 100 mm/h.
• C-Reactive Protein (CRP): Markedly elevated; often considered more sensitive than ESR.
• Complete Blood Count: Normochromic normocytic anemia of chronic disease and reactive thrombocytosis.

Imaging Modalities & Findings

• Color Doppler Ultrasound of Temporal Artery:
• PET/CT or MR Angiography:

• Uncomplicated GCA
  Cranial or systemic symptoms without ischemic complications (vision loss).
• Complicated GCA
  Presents with ischemic complications, specifically vision loss or stroke.

Second-Line & Adjunctive Therapy

Tocilizumab (IL-6 receptor antagonist) 162 mg subcutaneously weekly. Approved as a steroid-sparing agent; combining it with a 26-week prednisone taper results in higher sustained remission rates compared to steroids alone.

Surgical & Procedural Management

Temporal Artery Biopsy for diagnosis (should be performed within 1-2 weeks of starting steroids, as histopathology can remain positive for several weeks).

Recommended Lifestyle Changes

• Calcium (1200 mg) and Vitamin D (800 IU) supplementation to prevent steroid-induced osteoporosis.
• Weight-bearing exercise to preserve bone density.
• Monitor dietary sodium and carbohydrates due to high-dose steroid therapy.

Patient Counseling & Advice

Warn the patient that the disease can cause sudden blindness and they must report any visual changes immediately. Explain that steroids are life-saving but will cause side effects (weight gain, mood changes, insomnia) and cannot be stopped abruptly.

Follow-Up & Monitoring Schedule

Monitor clinical symptoms and ESR/CRP every 2-4 weeks during initial steroid taper. DEXA scan at baseline to evaluate bone mineral density. Annual chest X-ray or echocardiogram/CT to screen for late complication of aortic aneurysm.

Preventive Strategies

No known prevention for the disease itself. Prevention focuses on avoiding ischemic complications through rapid diagnosis and early treatment, and preventing drug toxicity (osteoporosis prophylaxis).

Overall life expectancy is equivalent to the age-matched general population. Vision loss, if it occurs, is usually permanent. Relapses are common (up to 50%) during steroid tapering, requiring an increase in dose or addition of Tocilizumab.