Pre-Rituximab Investigations for CNS Vasculitis
Before initiating rituximab for CNS vasculitis, you must screen for hepatitis B (HBsAg and anti-HBc), obtain baseline complete blood counts with differential and platelets, measure serum immunoglobulin levels (IgG, IgM, IgA), test for hepatitis C antibodies, and screen for latent tuberculosis. 1
Essential Baseline Screening
Infectious Disease Screening
The FDA label for rituximab explicitly mandates specific pre-treatment testing 1:
Hepatitis B virus (HBV) screening is critical and non-negotiable. Measure both HBsAg and anti-HBc before the first dose. HBV reactivation with rituximab can cause fatal acute hepatitis, even in patients with resolved or occult infection 2, 1. If HBV markers are positive, consult hepatology regarding antiviral prophylaxis before starting rituximab.
Latent tuberculosis screening is required given the profound immunosuppression rituximab causes 3, 1
Hematologic Baseline
Obtain complete blood counts (CBC) with differential and platelet counts prior to the first rituximab dose 1. This establishes your baseline for monitoring treatment-related cytopenias, which can be severe.
Immunologic Assessment
Measure baseline serum immunoglobulin levels (IgG, IgM, IgA) before each rituximab course 4, 1. This is essential because rituximab can cause secondary immunodeficiency and hypogammaglobulinemia, increasing infection risk 5, 3. Patients with pre-existing low immunoglobulin levels require heightened infection surveillance.
Disease-Specific Considerations
CNS Vasculitis Confirmation
Before attributing symptoms to CNS vasculitis and starting rituximab, ensure the diagnosis is secure. The differential diagnosis is broad, and mimickers like intracranial atherosclerosis and reversible cerebral vasoconstriction syndrome are common 6, 7. Ideally, diagnosis should be confirmed by:
- Brain/leptomeningeal biopsy showing necrotizing vasculitis (most definitive) 8, 6
- Cerebrospinal fluid analysis showing pleocytosis or elevated protein 6
- Vascular imaging (MRA/conventional angiography) demonstrating vessel wall irregularities, beading, or stenosis 6
- MRI showing vessel wall, parenchymal, or leptomeningeal enhancement 6
Exclude Secondary Causes
Determine whether the vasculitis is primary CNS vasculitis or secondary to systemic disease, infection, malignancy, or drugs 6, 7. This workup should include:
- Systemic vasculitis markers (ANCA testing if not already done) 9, 8
- Infectious workup including VZV serology/CSF PCR, neurosyphilis testing, HIV testing 10
- Evaluation for systemic inflammatory conditions
Monitoring During Treatment
Once rituximab is initiated:
- Monitor CBC with differential and platelets at 2-4 month intervals during therapy 11, 1
- Continue monitoring for cytopenias after the final dose until resolution 1
- Remeasure immunoglobulin levels prior to each rituximab course to detect progressive hypogammaglobulinemia 4
- Provide Pneumocystis jirovecii pneumonia (PCP) prophylaxis with trimethoprim-sulfamethoxazole given the high-dose glucocorticoids typically used concurrently 4, 11
Critical Safety Considerations
Progressive multifocal leukoencephalopathy (PML) is a devastating complication of rituximab, including fatal cases 3, 1. Maintain high suspicion for JC virus reactivation in any patient developing new CNS symptoms during or after rituximab treatment. Notably, PML has occurred in myositis patients who never received rituximab, so the baseline risk in immunosuppressed patients with CNS disease may already be elevated 3.
The most common serious adverse events with rituximab are infusion reactions and infectious complications 12, 1. Appropriate premedication and medical support for managing severe infusion reactions must be available 1.