A 62-year-old man is brought to the clinic by his wife because of rapidly worsening memory problems over the past 3 months. She reports that he was previously independent and cognitively intact but has developed confusion, difficulty recognizing familiar objects, and frequent mood changes. Over the past 2 weeks, he has had several episodes of involuntary jerking movements of his arms, especially when startled. Review of systems is notable for insomnia and unintentional weight loss. He has no fever, headache, or visual changes. Past medical history is unremarkable. He takes no medications. Family history is negative for neurodegenerative disease. He does not smoke, drink alcohol, or use illicit drugs. Vital signs are within normal limits. On physical examination, he is disoriented to time and place. Neurologic examination shows hyperreflexia and intermittent myoclonic jerks of the upper extremities. MRI of the brain demonstrates bilateral hyperintensity of the caudate nucleus and putamen on diffusion-weighted imaging. An electroencephalogram (EEG) shows periodic sharp wave complexes.
B) Creutzfeldt-Jakob disease
Creutzfeldt-Jakob disease (CJD) is a rapidly progressive, fatal neurodegenerative disorder caused by misfolded prion proteins (PrPScc) that induce abnormal folding of normal cellular prion protein (PrPC). Classic features include rapidly progressive dementia, myoclonus, and characteristic findings on diagnostic studies. MRI typically shows diffusion-weighted hyperintensity in the basal ganglia, and EEG often demonstrates periodic sharp wave complexes. The disease progresses over weeks to months and is uniformly fatal.
Answer choice A: Alzheimer disease, is incorrect. Alzheimer disease presents with slowly progressive cognitive decline over years, not months. Myoclonus and characteristic EEG findings are not typical, and MRI does not show basal ganglia diffusion restriction. Alzheimer disease is associated with β-amyloid plaques and neurofibrillary tangles composed of hyperphosphorylated tau.
Answer choice C: Dementia with Lewy bodies, is incorrect. Dementia with Lewy bodies is characterized by fluctuating cognition, visual hallucinations, rapid eye movement (REM) sleep behavior disorder, and parkinsonism. While dementia is present, the progression is not as rapid as in CJD, and EEG and MRI findings described here are not typical.
Answer choice D: Huntington disease, is incorrect.Huntington disease presents with choreiform movements, psychiatric changes, and cognitive decline, typically beginning in mid-adulthood. It is inherited in an autosomal dominant fashion and progresses over years, not months. MRI shows caudate nucleus atrophy rather than diffusion hyperintensity.
Answer choice E: Subacute combined degeneration, is incorrect. Subacute combined degeneration results from vitamin B12 deficiency and affects the dorsal columns and corticospinal tracts, leading to sensory ataxia, weakness, and paresthesias. Dementia and myoclonus are not primary features, and MRI findings of the basal ganglia are not expected.
Key Learning Point
Creutzfeldt-Jakob disease causes rapidly progressive dementia with myoclonus and characteristic MRI (basal ganglia diffusion restriction) and EEG (periodic sharp wave complexes) findings due to prion-mediated neurodegeneration.
