How to Identify SSPE in Children with a History of Measles
Diagnose SSPE through the combination of characteristic clinical features (progressive neurological decline with myoclonic jerks), elevated CSF/serum measles antibody ratio, and EEG showing periodic complexes that correlate 1:1 with myoclonic movements. 1, 2
Clinical Presentation to Recognize
Classic Progressive Pattern
- Insidious onset with subtle personality changes and declining intellectual performance that progresses to mental deterioration, seizures, myoclonic jerks, motor signs, coma, and death 1, 2
- Motor regression occurs in virtually all patients (100%), with cognitive decline in 86% 3
- Myoclonic seizures are the most common seizure type (74%), though focal (10%) and generalized tonic-clonic seizures (16%) also occur 3
Atypical Presentations Are Common
- Visual impairment, focal seizures, headache, vomiting, and movement disorders may be the initial manifestations 4
- Some patients present with only visual symptoms for weeks before rapid neurological deterioration 5
- Recent cases show progressively shorter latency periods (as short as 2-4 months after measles infection) and younger age at onset (even toddlers and infants), making early recognition critical 6, 4
Diagnostic Testing Algorithm
Essential Laboratory Confirmation
- Measure CSF and serum measles antibody titers to calculate the measles antibody index (CSF/serum ratio) - this demonstrates intrathecal synthesis of measles-specific antibodies and is the crucial diagnostic criterion 2, 4, 5
- The elevated CSF/serum measles antibody ratio is positive in 100% of confirmed cases 3
- CSF PCR for measles virus RNA can be performed, though antibody testing is often more reliable for SSPE diagnosis 2
Electroencephalography
- EEG reveals well-defined periodic complexes with a 1:1 relationship with the myoclonic jerks - this is pathognomonic for SSPE 1, 2
- Burst-suppression pattern on EEG is present in 100% of cases, though may not be evident at initial presentation 4, 3
- Repeat EEG if initial study is normal but clinical suspicion remains high 4
Neuroimaging
- Initial MRI is frequently normal (in up to 67% of cases at presentation), so a normal MRI does not exclude SSPE 4
- When abnormal, MRI may show focal or widespread white matter changes, or changes in subcortical and deep white matter 1, 4
- MRI is more useful for excluding alternative diagnoses than confirming SSPE 4, 5
Critical Historical Features
Measles Exposure Timing
- Traditional latency period is 2-10 years after measles infection, with typical presentation at 8-11 years of age 6
- Recent epidemiological shift shows dramatically shorter latency periods (2-6 years, or even 2-4 months) and younger age at onset (as young as 2-3 years) 6, 4
- History of measles infection is present in approximately 62% of cases, though some patients may have had unrecognized infection 3
Vaccination Status
- Most patients have received measles vaccination (86%), but this does not prevent SSPE if they had prior natural measles infection 3
- SSPE results from natural measles virus infection, not from vaccination - children who developed SSPE after vaccination likely had unrecognized measles infection before vaccination 2
Important Clinical Pitfalls
Don't Wait for Classic Features
- Investigate for SSPE even in infants or toddlers with compatible clinical features and recent measles history, as the latency period is decreasing 6, 4
- Atypical presentations (visual symptoms, focal seizures, movement disorders) are common and should not delay diagnostic workup 4, 5
Don't Rely on Single Test
- Normal initial MRI occurs in the majority of cases and should not exclude the diagnosis 4
- EEG may not show characteristic findings at first presentation - repeat if clinical suspicion persists 4
- The combination of clinical features, elevated CSF/serum measles antibody ratio, and characteristic EEG findings establishes the diagnosis 2, 5, 3