Introduction: Rapidly progressive dementia includes a heterogeneous group of disorders. Electroencephalography (EEG) is one
of the most important diagnostic tests, especially in the context of disorders such as Creutzfeldt–Jakob disease (CJD), autoimmune
encephalitis, metabolic encephalopathy, and non-convulsive status epilepticus.
Case Report: A 78-year-old female with no known comorbidities presented with painless, progressive diminution of vision
in both eyes over 4 months, followed by abnormal involuntary movements and rapidly progressive cognitive decline. She was
referred to our centre after showing no improvement with empirical immunotherapy. On examination, she had altered sensorium,
paucity of movements on the right side, and myoclonic jerks. EEG was performed and showed generalized theta slowing with
stereotyped periodic sharp wave complexes (PSWCs). Magnetic resonance imaging (MRI) of the brain with diffusion-weighted
imaging demonstrated diffuse asymmetric cortical restricted diffusion involving the bilateral cerebral cortices (left more than right),
consistent with cortical ribboning. Cerebrospinal fluid (CSF) analysis was positive for the 14-3-3 protein. A diagnosis of sporadic
CJD was made.
Discussion: The main EEG abnormality in sporadic CJD is the presence of periodic discharges (PSWCs). EEG abnormalities
vary depending on stage of the disease. Periodic discharges that mimic CJD can occur in metabolic encephalopathy, autoimmune
encephalitis, lithium toxicity, anoxic injury, and sometimes in nonconvulsive status epilepticus; however, these typically lack the
highly stereotyped 1-Hz periodicity seen in sporadic CJD, particularly when correlated with the clinical progression.
Conclusion: EEG has significant clinical utility. It helps distinguish CJD from autoimmune encephalitis and nonconvulsive status
epilepticus, in patients with rapidly progressive dementia when used in conjunction with MRI and CSF prion assays.