How is Primary Angiitis of the Central Nervous System diagnosed
How is the clinical diagnosis of PACNS/PCNSV confirmed?
• First: diagnosis is challenging, and careful exclusion of its mimics is essential.
• Laboratory: elevated ESR/CRP, anemia of chronic disease, and thrombocytosis may or may not be present. If abnormal, another systemic or infectious disease should also be considered. An intravascular lymphoma mimicking PACNS/PCNSV must be excluded in patients with an elevated serum lactate dehydrogenase (>3× upper limit of normal).
• CSF: lymphocytic pleocytosis (median 20 cells/μL) and elevated protein (median 120 mg/dL) in 80% to 90% of patients. High IgG index and oligoclonal bands can occasionally be seen. If CSF is normal, another condition like RCVS should be considered (see Question 33).
• Angiogram: alternating areas of stenosis and ectasia in multiple vessels in more than a single vascular bed. Sensitivity is 56% to 90% and predictive value is 30% to 50%. Cannot visualize vessels <500 μm in diameter. CTA and MRA are less sensitive than catheter angiogram.
• Brain MRI: almost always abnormal but nonspecific with predictive value of 40% to 70%. Cortical/subcortical infarcts (50%), white matter hyperintensities, and gadolinium-enhanced intracranial lesions (33%) are seen most commonly. Gadolinium-enhanced leptomeninges is common in ABRA.
• Brain biopsy (gold standard): granulomatous vasculitis is more diagnostic than lymphocytic vasculitis. Highest yield is from a lesion. Cannot be obtained from needle biopsy. If no lesion, then biopsy leptomeninges and cortex from nondominant temporal lobe. Sensitivity is 75% and specificity is 90% to 100% in patients subsequently diagnosed with definite PACNS/PCNSV. Importantly, in patients who undergo biopsy who turn out to not have PACNS/PCNSV, an alternative diagnosis is found in 40% to 50% patients. Note that patients with an abnormal cerebral angiogram frequently have a normal leptomeningeal MRI and biopsy, whereas patients with leptomeningeal enhancement on MRI and a normal cerebral angiogram are more likely to have an abnormal leptomeningeal biopsy due to the size of the vessel involved.
