Is measles Immunoglobulin G (IgG) extremely elevated during subacute sclerosing panencephalitis (SSPE)?

Measles IgG in SSPE

Yes, measles IgG is extremely elevated in both serum and cerebrospinal fluid (CSF) during subacute sclerosing panencephalitis (SSPE), including during any "silent" or latent period—this extreme elevation is a defining diagnostic feature of the disease. 1

Diagnostic Antibody Pattern in SSPE

The hallmark of SSPE is extraordinarily high measles-specific IgG titers in both serum and CSF, with a CSF/serum measles antibody index ≥1.5 confirming intrathecal antibody synthesis. 1 This elevated index indicates local CNS production of antibodies rather than simple leakage from serum. 1

Key Diagnostic Features:

• All SSPE patients (100%) maintain extremely elevated measles-specific IgG antibodies regardless of disease stage, whether in early, progressive, or advanced phases. 1, 2

• The CSF/serum measles antibody index ranges from 2.3 to 36.9 (mean: 12.9), demonstrating massive intrathecal antibody production. 3

• When combined with persistent measles-specific IgM and CSF/serum index ≥1.5, diagnostic accuracy reaches 100% sensitivity and 93.3% specificity for SSPE. 1

The Persistent IgM Phenomenon

A critical distinguishing feature is that SSPE patients maintain detectable measles-specific IgM antibodies in both serum and CSF years after the initial measles infection—this is highly abnormal since IgM typically disappears within 30-60 days after acute measles. 1

• In 35% of SSPE cases, the specific IgM response is more pronounced in CSF than in serum, indicating IgM production within the CNS itself. 2

• This persistent IgM reflects ongoing immune stimulation from continuous CNS viral replication, not acute infection. 1, 2

• The continuing release of measles antigen from persistent virus in the CNS prevents the normal shut-off of IgM synthesis. 2

Distinguishing SSPE from Other Conditions

The isolated, extremely strong measles antibody response distinguishes SSPE from multiple sclerosis, which shows the MRZ reaction (intrathecal synthesis against at least two of three viral agents: measles, rubella, zoster). 1, 4

The persistent IgM years after potential measles exposure distinguishes SSPE from:

• Acute measles infection (where IgM disappears within 30-60 days) 1
• Measles reinfection (which shows high-avidity IgG with transient IgM) 1
• False-positive IgM results (which lack the extremely high titers and elevated CSF/serum index) 1

Clinical Algorithm for Diagnosis

When SSPE is suspected based on progressive neurological symptoms:

1. Obtain simultaneous serum and CSF samples for measles-specific IgG measurement. 1

2. Calculate the CSF/serum measles antibody index—values ≥1.5 confirm intrathecal synthesis. 1

3. Test for persistent measles IgM in both serum and CSF—presence years after potential measles exposure strongly suggests SSPE. 1

4. Confirm with characteristic EEG findings showing periodic complexes with 1:1 relationship to myoclonic jerks. 4

5. Consider PCR testing of CSF for measles virus RNA and oligoclonal bands with immunoblotting against measles virus proteins. 4

Critical Caveat About "Silent" SSPE

There is no truly "silent" period once SSPE develops—the extremely elevated IgG and persistent IgM indicate active CNS viral replication from disease onset. 1, 2 The latency period (typically 2-10 years) between acute measles infection and SSPE symptom onset represents true viral dormancy with no systemic viremia and no active immune stimulation. 1 Once SSPE begins, even if symptoms are subtle, the antibody response is already dramatically elevated. 2

Prevention Remains the Only Effective Strategy

Measles vaccination is the only effective prevention for SSPE and has essentially eliminated the disease in highly vaccinated populations. 1, 4, 5 The MMR vaccine does not increase SSPE risk—cases reported after vaccination likely resulted from unrecognized measles infection before vaccination. 4, 5