Silent Progression of Adult-Onset SSPE: From Ocular Onset to Evolving EEG

BackgroundSubacute sclerosing panencephalitis (SSPE) is a rare progressive encephalitis due to persistent measles infection. While classically a childhood disorder, atypical, adult-onset, and subclinical variants are increasingly reported. Ocular findings may precede neurological involvement by years. We aimed to underline EEG's role in tracking disease evolution from isolated ocular signs to neurological progression.CaseA 31-year-old woman presented with isolated ocular complaints and bilateral optic atrophy. Cerebrospinal fluid revealed measles IgG and IgG index positivity, confirming SSPE. For four years, she remained neurologically asymptomatic. EEG initially showed bilateral central theta paroxysms, later progressing to generalized periodic discharges. Serial EEGs demonstrated progressively shortened inter-discharge intervals. Additional features emerged, including frontally predominant generalized rhythmic delta activity and hyperventilation-provoked discharges. Importantly, when EEG abnormalities first appeared, neuropsychometric testing detected deficits in attention and executive function, despite the absence of subjective complaints. With time, cognitive decline became clinically evident, and negative myoclonus appeared.ConclusionThis case illustrates the importance of long-term surveillance in subclinical SSPE. EEG abnormalities preceded overt neurological decline, providing the earliest clues to disease progression. Careful interpretation of evolving EEG patterns may anticipate cognitive impairment and guide timely interventions. Our patient's trajectory underscores that even clinically silent SSPE carries a hidden risk of deterioration, and that vigilant EEG monitoring can act as a window into the disease course.