What is the best approach to diagnose and manage a patient with suspected Giant Cell Arteritis (GCA) when only Computed Tomography (CT) imaging is available?

Diagnostic and Management Approach for Suspected GCA with CT-Only Access

When only CT imaging is available for suspected Giant Cell Arteritis, use CT angiography (CTA) of the neck/chest/abdomen/pelvis to evaluate for large vessel involvement and extracranial arterial inflammation, while recognizing that CT is not recommended for cranial artery assessment and temporal artery biopsy remains the preferred diagnostic test for cranial GCA. 1

Diagnostic Strategy

Initial Diagnostic Approach

• Proceed with temporal artery biopsy as the primary diagnostic test for suspected cranial GCA, obtaining a unilateral long-segment specimen (>1 cm) within 2 weeks of starting glucocorticoids 1, 2
• Temporal artery biopsy remains the gold standard over imaging modalities due to widespread availability and validation 1, 2
• Do not delay treatment while awaiting biopsy or imaging—start high-dose glucocorticoids immediately if clinical suspicion is high, as untreated GCA can cause irreversible blindness 2, 3

Role of CT When Available

• CT and PET are explicitly not recommended for assessment of cranial arteries due to lack of evidence, radiation exposure, and high resource use 1
• CTA may be used for detecting large vessel involvement (extracranial arteries, aorta) to support diagnosis of large vessel GCA, particularly in patients with predominantly systemic symptoms rather than cranial symptoms 1, 4
• CTA has demonstrated 67-73% sensitivity and 85-98% specificity for GCA diagnosis, with wall thickness measurements showing 67% sensitivity and 98% specificity 4
• An aortic wall thickness ≥2.2 mm on CT is the optimal threshold for diagnosing GCA-related aortitis (sensitivity 67%, specificity 98%) 5

When Temporal Artery Biopsy is Negative

• If biopsy is negative but clinical suspicion remains high, obtain CTA of neck/chest/abdomen/pelvis to evaluate for extracranial large vessel GCA 1, 4
• This approach may reveal aortitis, subclavian/axillary arteritis, or other large vessel involvement that would not be detected by temporal artery biopsy alone 1, 6
• Approximately one-third of GCA patients have no temporal artery involvement, making large vessel imaging essential in these cases 6

Treatment Initiation

Patients WITHOUT Visual Symptoms or Critical Cranial Ischemia

• Start high-dose oral prednisone 1 mg/kg/day (up to 80 mg) given daily rather than alternate-day dosing 1, 2
• High-dose oral glucocorticoids are preferred over IV pulse glucocorticoids in this population, as routine IV pulse therapy increases infection risk that may outweigh benefits, especially in elderly patients 1, 2
• Strongly consider adding tocilizumab with high-dose oral glucocorticoids for glucocorticoid-sparing effect and improved remission rates 1, 2

Patients WITH Visual Symptoms, Vision Loss, or Critical Cranial Ischemia

• Immediately initiate IV pulse methylprednisolone 500-1,000 mg/day for 3-5 days followed by high-dose oral glucocorticoids 1, 2
• Do not delay treatment while awaiting biopsy or imaging results 2, 3

Imaging Timing Considerations

Critical Timing Window

• Perform imaging (including CTA) before starting glucocorticoids or within 72 hours after initiation, as treatment rapidly reduces detectability of vascular inflammation 1, 4, 6
• Temporal artery biopsy can still show histopathologic changes up to 2 weeks after starting glucocorticoids, but sensitivity decreases over time 2
• All imaging modalities have reduced sensitivity after glucocorticoid initiation 6

Practical Algorithm When CT is Your Only Option

1. High clinical suspicion (headache, jaw claudication, visual symptoms, elevated ESR/CRP in patient >50 years):

   • Start high-dose glucocorticoids immediately 2, 3
   • Obtain temporal artery biopsy within 2 weeks 1, 2
   • If biopsy negative and suspicion remains high, obtain CTA of neck/chest/abdomen/pelvis to evaluate for large vessel involvement 1, 4

2. Predominantly systemic symptoms (fever, weight loss, malaise) without cranial symptoms:

   • Start high-dose glucocorticoids 2
   • Consider CTA of neck/chest/abdomen/pelvis as primary imaging to evaluate for large vessel GCA and aortitis 1, 4, 6
   • Temporal artery biopsy may still be obtained but has lower yield in this presentation 6

3. Negative temporal artery biopsy but persistent clinical suspicion:

   • Obtain CTA to evaluate for extracranial large vessel involvement 1, 4
   • Look for aortic wall thickening ≥2.2 mm, arterial wall thickening, or luminal changes in subclavian, axillary, or carotid arteries 4, 5

Important Caveats

Limitations of CT

• CT cannot reliably assess temporal arteries for GCA—no studies validate this approach and guidelines explicitly recommend against it 1
• CT exposes patients to significant radiation, making it less suitable for repeated monitoring compared to ultrasound or MRI 1
• CTA cannot reliably distinguish between active inflammation and vascular remodeling in treated patients 4
• False-positive findings can occur with atherosclerosis, requiring correlation with clinical and laboratory findings 4

Baseline Large Vessel Assessment

• Obtain baseline CTA to evaluate for aneurysms, stenoses, and large vessel involvement at diagnosis, as this guides subsequent monitoring for structural complications 2
• The aorta should be routinely assessed in all GCA patients at diagnosis and during follow-up 6

Monitoring Considerations

• For suspected relapse with unreliable inflammatory markers, CTA may be considered for assessment of vessel abnormalities 1, 4
• For long-term monitoring of structural damage (aneurysms, stenoses), CTA or MRA may be used 1, 4
• Imaging is not routinely recommended for patients in clinical and biochemical remission 1