In a 9‑month‑old who recovered from measles one week ago and now has 1–2 brief daily startle episodes without fever, altered consciousness, focal neurological findings, or post‑ictal period, are these episodes benign myoclonus or indicative of seizure or measles encephalitis?

Urgent Evaluation Required for Possible Measles Encephalitis

In a 9-month-old recovering from measles who now presents with new startle episodes one week later, these events warrant immediate diagnostic workup for measles encephalitis, as this timing falls within the typical 10-day window for acute neurological complications, which occur in approximately 1 per 1,000 measles cases and carry significant risk of permanent brain damage or death. 1, 2

Why This Cannot Be Dismissed as Benign

• Measles encephalitis typically presents with neurological symptoms appearing during or shortly after the acute illness, with onset around 10 days after initial infection—exactly matching this patient's timeline of one week post-recovery 1, 2
• The case-fatality rate for measles is 1-2 per 1,000 cases, with encephalitis being one of the two most common causes of death, and survivors often suffer permanent brain damage 1, 2
• Age under 12 months at measles infection is a significant risk factor for severe complications, including later development of subacute sclerosing panencephalitis (SSPE), which occurs in approximately 4-11 per 100,000 measles-infected individuals 1, 3

Critical Diagnostic Workup Required Immediately

Cerebrospinal fluid analysis with measles-specific testing:

• Perform lumbar puncture with PCR for measles virus and measles-specific IgM to confirm or exclude encephalitis 1
• CSF analysis showing intrathecal antibody synthesis is diagnostic for measles CNS involvement 2

Neuroimaging:

• Obtain MRI brain (not CT) as the preferred imaging modality for detecting encephalitic changes 1
• MRI has superior sensitivity for detecting parenchymal injury and inflammatory changes associated with measles encephalitis 4

Electroencephalogram:

• Perform EEG, though findings are usually nonspecific in acute measles encephalitis 1
• EEG helps differentiate seizure activity from other movement disorders 4

Additional confirmatory testing:

• Obtain serum and urine measles-specific IgM for additional diagnostic confirmation 1

Clinical Features That Distinguish Encephalitis from Benign Events

Red flags for measles encephalitis (any of these mandate urgent evaluation):

• Fever accompanying the neurological symptoms 1, 2
• Altered mental status or decreased responsiveness 1, 2
• Seizures (distinct from simple startle responses) 1, 2
• Focal neurological deficits 1
• Behavioral changes or personality alterations 2

Features suggesting benign myoclonus:

• Episodes occur only when awake and alert 4
• No alteration in consciousness during or after episodes 4
• Child returns to baseline immediately between episodes 4
• No fever present 1
• Normal developmental interaction and responsiveness 1

Management Based on Findings

If measles encephalitis is confirmed:

• Provide supportive care with aggressive fever control using acetaminophen or ibuprofen (avoid aspirin due to Reye syndrome risk) 1, 2
• Administer vitamin A supplementation: 200,000 IU orally for this 9-month-old infant (repeat on day 2 for complicated measles) 1
• Treat any secondary bacterial infections with appropriate antibiotics 1, 2
• No antiviral therapy is recommended for acute measles encephalitis in immunocompetent children; aciclovir is ineffective 1
• Manage seizures with standard anticonvulsant protocols if they occur 2

If workup is negative for encephalitis:

• Reassure caregivers that simple febrile seizures or benign myoclonus do not increase risk of epilepsy 1
• Continue routine care and standard vaccination schedule 1
• Educate on fever management for future episodes 1

Long-Term Surveillance Considerations

• Monitor for SSPE development over the next 6-8 years, as this infant's young age at infection (9 months) places them at higher risk 1, 3
• SSPE typically presents years later with personality changes, cognitive decline, and myoclonic jerks 1, 2
• Early signs include subtle behavioral changes and intellectual decline, usually emerging several years after initial measles infection 1

Critical Pitfalls to Avoid

• Do not dismiss new neurological symptoms as "just recovery"—early recognition of encephalitis is critical, as the first week after apparent recovery falls within the typical window for measles encephalitis complications 1
• Do not postpone diagnostic workup when concerning features are present—measles encephalitis requires urgent evaluation and supportive care to minimize morbidity and mortality 1
• Do not withhold future measles-containing vaccinations because of this episode—vaccination remains the only proven prevention for SSPE and future measles complications 1, 3
• Do not use aspirin for fever control in this infant due to the risk of Reye syndrome 1, 2

When to Activate Emergency Medical Services

Immediate EMS activation is required for: 4

• Seizure lasting more than 5 minutes 4
• Multiple seizures without return to baseline between episodes 4
• Altered consciousness that does not return to baseline within 5-10 minutes after episode stops 4
• Difficulty breathing or respiratory distress 4
• Any traumatic injury associated with the episodes 4