Would Subacute Sclerosing Panencephalitis (SSPE) show in the cerebrospinal fluid (CSF)?

SSPE and Cerebrospinal Fluid Findings

Yes, SSPE definitively shows characteristic abnormalities in the CSF, most notably markedly elevated measles-specific antibodies with an elevated CSF/serum antibody index, which is the diagnostic cornerstone of this disease. 1

Diagnostic CSF Abnormalities in SSPE

The hallmark CSF finding in SSPE is dramatically elevated measles-specific antibodies with intrathecal synthesis, demonstrated by a CSF/serum measles antibody index (CSQrel) ≥ 1.5, with typical values ranging from 2.3 to 36.9 in confirmed cases. 2 This elevated antibody index reflects local antibody production within the central nervous system rather than passive transfer from serum. 3

Key CSF Parameters in SSPE:

• Measles-specific IgG: Markedly elevated in CSF with higher concentrations than would be expected from serum alone, indicating intrathecal synthesis 2, 4

• Measles-specific IgM: Present in CSF at levels higher than serum (when CSF is diluted 1:5 compared to serum diluted 1:50), reflecting ongoing local immune response 5

• Oligoclonal IgG bands: Demonstrated on immunofixation electrophoresis or isoelectric focusing, showing identical patterns in CSF and serum 6, 3

• Total protein: May be elevated, though typically not as dramatically as in bacterial infections 6

• Cell count: Usually shows mild lymphocytic pleocytosis or may be normal 1

• Glucose: Characteristically normal, helping distinguish SSPE from bacterial or tuberculous meningitis 6

Clinical Context for CSF Testing

When white matter lesions are identified on neuroimaging, measles virus testing for SSPE should be performed on CSF, as recommended by the International Encephalitis Consortium. 1 This is particularly important in patients presenting with subacute progressive neurological deterioration, myoclonic jerks, and characteristic EEG findings (periodic high-amplitude slow waves). 6, 4

Diagnostic Algorithm:

1. Obtain simultaneous serum and CSF samples for measles antibody testing to calculate the antibody index 2

2. Calculate CSF/serum antibody index (CSQrel): A value ≥ 1.5 confirms intrathecal measles antibody synthesis and supports the diagnosis of SSPE 2

3. Perform CSF immunofixation electrophoresis to demonstrate oligoclonal IgG bands if antibody index testing is unavailable or equivocal 6, 3

4. Measure both IgG and IgM measles-specific antibodies in CSF, as both are typically elevated and remain constant over the disease course 5

Common Pitfalls to Avoid

Do not rely solely on serum measles antibodies – the diagnosis of SSPE requires demonstration of intrathecal antibody synthesis through the CSF/serum antibody index, not just elevated serum titers. 2, 4

Do not dismiss SSPE if CSF cell count is normal – unlike acute viral encephalitis, SSPE may present with minimal or no CSF pleocytosis despite significant CNS pathology. 1

Brain biopsy is indicated only when CSF serology is negative or equivocal in a clinically suspected case, as the CSF antibody findings are sufficiently diagnostic in the vast majority of cases. 4

Supporting Laboratory Evidence

The CSF findings should be interpreted alongside:

• EEG showing periodic high-amplitude slow waves (characteristic but not specific) 6, 4

• MRI demonstrating high signal intensity lesions in subcortical white matter on T2-weighted images 1, 6

• Clinical history of measles infection (often in unvaccinated individuals or those infected at very young ages) occurring years before SSPE onset 2, 6

The antibody titers in SSPE remain elevated and constant throughout the disease course, distinguishing this from acute measles encephalitis where antibody levels would be expected to decline over time. 5