Giant Cell Arteritis

01Pathophysiology

Giant cell arteritis (GCA) is a granulomatous vasculitis that targets medium and large arteries, with a strong predilection for branches of the external carotid artery, most notably the temporal artery. The disease can also involve the ophthalmic artery, vertebral arteries, and the aorta itself.

The process begins when dendritic cells in the adventitia of the arterial wall become activated and recruit CD4+ T-helper cells. These T cells, predominantly of the Th1 and Th17 subtype, release interferon-gamma and interleukin-17, which in turn activate macrophages within the vessel wall. The macrophages fuse to form multinucleated giant cells, the histopathologic hallmark of the disease, which concentrate near the internal elastic lamina of the media. This granulomatous infiltration damages and fragments the internal elastic lamina.

The downstream consequence is intimal hyperplasia, which progressively narrows the arterial lumen. This luminal narrowing produces ischemia in the territories supplied by the affected vessels. This mechanism directly explains why the patient develops a new headache (ischemia of the temporal artery territory), jaw claudication (ischemia of the maxillary artery supplying the masseter), and, most critically, visual loss from anterior ischemic optic neuropathy (AION) when the posterior ciliary branches of the ophthalmic artery are occluded.

Systemically, the intense inflammatory response drives the liver to produce large amounts of acute-phase reactants, which is why the ESR and CRP are almost always markedly elevated. The cytokine storm also accounts for constitutional symptoms such as fever, malaise, and weight loss.

Understanding this pathophysiology is important because the vignette will often describe "claudication" of the jaw or tongue during chewing. This is not muscle disease; it is vascular insufficiency caused by luminal stenosis. Similarly, sudden monocular vision loss in an elderly patient with headache and elevated ESR is not a stroke of the central retinal artery from an embolus; it is ischemia from inflammation-driven narrowing of the ophthalmic artery branches.

02Classification and Clinical Manifestation

GCA can be classified based on its predominant vascular involvement:

Clinical Manifestation Table:

03Diagnostic Workup

When the vignette presents an elderly patient (age $\ge \backslash geq$ 50) with new-onset headache, jaw claudication, and/or visual symptoms, the first step is to order ESR and CRP. These are the best initial tests. A markedly elevated ESR (classically $>50>\; 50$ mm/hr by Westergren method, frequently $>100>\; 100$) in this clinical context is highly suggestive.

The most accurate test and gold standard for diagnosis is the temporal artery biopsy. The biopsy specimen should be at least 1 to 2 cm in length because GCA produces skip lesions, meaning segments of normal artery interspersed with inflamed segments. A short biopsy risks sampling a normal skip area and yielding a false-negative result. If the first biopsy is negative but clinical suspicion remains high, a contralateral temporal artery biopsy should be performed.

The critical exam-tested principle here is: do not delay corticosteroid treatment while waiting for the biopsy. Steroids should be started immediately upon clinical suspicion. The biopsy will remain positive for up to 2 to 4 weeks after starting glucocorticoids, so treatment first, biopsy second is the correct sequence.

Temporal artery duplex ultrasound showing the "halo sign" is increasingly recognized as a useful noninvasive diagnostic tool. In settings where experienced ultrasonography is available, a positive halo sign may support the diagnosis and, in some guidelines, reduce the need for biopsy. However, for exam purposes, temporal artery biopsy remains the gold standard.

For patients suspected of having large-vessel GCA (upper extremity claudication, asymmetric pulses, aortic regurgitation murmur), CT angiography or MR angiography of the aorta should be performed to evaluate for wall thickening, stenosis, or aneurysm formation.

04Management and Treatment

Acute Stabilization:

The moment GCA is clinically suspected, start corticosteroids immediately. This is the single most tested management principle. For a patient without visual symptoms, begin oral prednisone at 40-60 mg/day. For a patient presenting with any visual complaint (transient vision loss, diplopia, or established vision loss), escalate to IV methylprednisolone 1 g/day for 3 consecutive days, then transition to oral prednisone 40-60 mg/day. The goal of aggressive IV dosing in visual-threatening disease is to prevent irreversible blindness in the contralateral eye; once vision is lost in one eye from AION, it rarely recovers, and the unaffected eye is at imminent risk.

Arrange a temporal artery biopsy within 2 weeks of starting steroids. Do not let the biopsy delay treatment.

Add low-dose aspirin (75-100 mg daily) to reduce ischemic complications.

Long-Term Management and Taper:

Glucocorticoid taper is slow and guided by clinical symptoms and inflammatory markers. A common approach:

• Maintain the initial dose for 2-4 weeks until symptoms resolve and ESR/CRP normalize.

• Reduce by approximately 10 mg every 2 weeks until reaching 20 mg/day.

• Then reduce by 2.5 mg every 2-4 weeks until reaching 10 mg/day.

• Then reduce by 1 mg every 1-2 months.

• Total treatment duration is typically 1 to 2 years, though some patients require longer courses.

Tocilizumab, an IL-6 receptor inhibitor, is now established as a steroid-sparing therapy. It is typically initiated alongside glucocorticoids to allow a faster taper, reduce the cumulative steroid burden, and lower the relapse rate. This is an increasingly tested drug name.

Contraindications and Cautions:

Prolonged high-dose steroid use carries well-known risks: osteoporosis, hyperglycemia, adrenal suppression, gastric ulceration, and opportunistic infections. All patients on long-term steroids should receive bone-protective therapy and be monitored for metabolic side effects. Patients should be screened for latent tuberculosis before starting tocilizumab.

Long-term surveillance for thoracic aortic aneurysm is essential, as GCA patients have a 17-fold increased risk of thoracic aortic aneurysm. Annual chest radiography or periodic CT/MR angiography should be considered.

05Differential Diagnosis and Distractors

06Traps and High-Yield Pearls

The single most tested trap with GCA is the management sequence. Students see "temporal artery biopsy is the gold standard" and instinctively select it as the next best step before treatment. This is incorrect. The correct answer is always to start high-dose corticosteroids first and arrange the biopsy afterward. Waiting for the biopsy delays treatment and puts the patient at risk for irreversible bilateral blindness. The biopsy remains diagnostic for 2 to 4 weeks after starting steroids, so there is no diagnostic penalty for treating first.

A second common pitfall involves recognizing that jaw claudication carries the highest positive likelihood ratio of any individual symptom for GCA. Students frequently anchor on headache or elevated ESR alone and overlook the significance of pain with chewing. If the vignette describes an elderly patient whose jaw "tires" or "aches" during meals, this is a strong signal pointing toward GCA over other causes of headache.

Third, students sometimes confuse GCA with Takayasu arteritis because both are granulomatous vasculitides of large vessels. The discriminator is age: GCA is a disease of patients $\ge 50\backslash geq\; 50$ years old, while Takayasu affects patients .

Fourth, be aware that a negative biopsy does not rule out GCA due to skip lesions. If the clinical picture is convincing and the first biopsy is negative, the next step is a contralateral biopsy, not abandoning the diagnosis.

Finally, students often forget the long-term complication: thoracic aortic aneurysm. A question may present a patient with a history of treated GCA who now has a widened mediastinum on chest imaging. The connection between prior GCA and aortic aneurysm is a tested association.

The core competency being tested across all GCA questions is the ability to recognize the clinical presentation in an elderly patient, prioritize immediate empiric treatment over confirmatory testing, and understand the rationale for urgent glucocorticoid therapy to prevent permanent vision loss.