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Arteritic AION (Giant Cell Arteritis)

CRITICAL — Neuro

Symptoms

sudden, painless, and severe vision loss

initially unilateral; high risk for rapid bilateral involvement

new-onset headache or scalp tenderness (e.g., pain with hair combing)

jaw claudication (pain while chewing)

polymyalgia rheumatica (proximal muscle/joint aches)

anorexia, weight loss, and low-grade fever

Clinical Findings

Ocular signs

visual acuity often counting fingers or worse
rapd and dyschromatopsia
pale, chalky-white disc edema (differs from sectoral edema of naion)
altitudinal or central visual field defects
possible concurrent central retinal artery occlusion (crao) or cn vi palsy

Systemic signs

palpable, tender, and non-pulsatile temporal artery

Stat labs

markedly elevated esr (men: >age/2; women: >[age+10]/2)
elevated crp (does not rise with age; highly sensitive)
thrombocytosis (elevated platelet count)

Etiology

Pathophysiology

granulomatous vasculitis of medium and large arteries
involves posterior ciliary arteries causing ischemic optic neuropathy
characterized by "skip lesions" (discontinuous inflammation)

Risk factors

age ≥55 (typically >70)
female predominance; caucasian/northern european ancestry
50% associated with polymyalgia rheumatica

Red Flags

any new vision loss in patients ≥55 years (requires stat labs)

jaw claudication or scalp tenderness (highly specific for gca)

fellow-eye involvement within days to weeks if untreated

chalky-white disc edema (aaion) vs sectoral edema (naion)

Investigations

Ocular evaluation

pupillary assessment for rapd and color plate testing
dilated fundus exam to rule out retinal etiologies

Stat laboratory

stat esr, crp, and platelet count (thrombocytosis)
esr may be normal in 10–20% of cases

Temporal artery biopsy

adequate specimen length (2–3 cm) to account for skip lesions
histology remains positive for up to 2 weeks after initiating steroids
do not delay steroid treatment while awaiting biopsy

Treatment

Acute steroids

iv methylprednisolone (1g daily for 3 days or 250mg q6h)
transition to oral prednisone (1mg/kg/day, usually 80–100mg)
transition to a very slow oral taper over 12–18 months

Adjuncts

steroid-sparing agents (e.g., tocilizumab or methotrexate) for refractory cases
ppi for gi protection and bisphosphonates/calcium for bone health
monitor blood glucose and symptoms during taper

Clinical Pearl

gca is the most common systemic vasculitis in adults >50. esr typically >50 (often >100), crp elevated — both together increase sensitivity. temporal artery biopsy: 15-20% false negative rate (skip lesions) — do not delay steroids for biopsy. fellow eye risk without treatment: 25-50% within days. steroids should be started immediately when gca is suspected — they do not significantly affect biopsy for up to 2 weeks.

Differential Diagnosis

non-arteritic aion (naion)
optic neuritis (presents with pain on eye movement)
compressive optic neuropathy (slowly progressive)
central retinal vein occlusion