Dear Editor,
Subacute Sclerosing Panencephalitis (SSPE) is a chronic encephalitis occurring after infection with measles virus. Typical electroencephalogram (EEG) is a minor criteria for diagnosing SSPE.[1] We report a rare atypical electroencephalographic finding in a child with SSPE.
The index child is a 7-year-old, previously well, developmentally normal, unimmunized boy presenting with myoclonic seizures and cognitive decline for 4 months. He stopped interacting with parents and could not dress/feed himself or indicate bowel/bladder needs. He did not have fever, rash, head injury, and was not exposed to drugs, toxins, and animal bite.
On examination, the child’s weight was 15 kg (<3z, WHO ref std), height 107 cm (<3z, WHO ref std), and head circumference 51 cm (0 to –2z, WHO ref std). He was apathetic, mute, and unresponsive. He did not have meningeal signs. His motor, sensory, cerebellar, and autonomic examination was unremarkable. He had flexion myoclonus occurring once every 5–10 min.
The child’s awake EEG [Figure 1] revealed continuous, synchronous background with abnormally slow 3–6 Hz delta/theta activity. Frequent, quasiperiodic 1 Hz, 200–300 μV (microvolts) epileptiform discharges were noted at intervals of 2–5 s throughout the record over left temporo-occipital region. No additional abnormalities were noted with photic stimulation.
Figure 1.
EEG epoch showing longitudinal montage application using 18–20 electrode placement system (sensitivity: 7.5 μV/mm, sweep speed: 30 mm/s, low-frequency filter: 0.5 Hz, high-frequency filter: 70 Hz, notch filter: 50 Hz). Lateralized periodic discharges (1–1.5 Hz, 200–250 μV) are noted (encircled in black) over P3–O1, T3–T5, and T5–O1
Child’s cerebrospinal fluid and serum titers of anti-measles antibodies were elevated, confirming the diagnosis of SSPE. His parents were counseled about the disease course and advised supportive care, isoprinosine, and follow-up.
Typical EEG in SSPE is characterized by quasiperiodic, high-voltage (300–1500 µV), repetitive polyspike and sharp and slow wave complexes (Radermecker complexes) occurring for a duration of 0.5–2 s, recurring every 4–12 s with slow background activity.[2,3] Though atypical EEGs have been reported in SSPE, isolated lateralized periodic discharges are rarely reported. Silva et al.[4] reported a case of 14-year-old child having SSPE with initial left temporal focus evolving to lateralized periodic discharges. The exact pathogenesis for atypical EEG pattern in SSPE is unclear. Lateralized periodic discharges in our patient may be hypothesized to be secondary to focal electrophysiological alteration secondary to viral proliferation.
Our case attempts to sensitize readers about atypical EEG in SSPE, thereby highlighting the importance of early anti-measles antibody titer estimation in case of clinical suspicion of SSPE despite atypical EEG.
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Conflicts of interest
There are no conflicts of interest.
REFERENCES
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