Prion-Associated Neurologic Disorders
Prion diseases (also known as transmissible spongiform encephalopathies) are chronic and progressive neurodegenerative disorders that can affect both humans and animals. Prions are pathogenic agents that are transmissible and consist of abnormal proteins. Known human forms include kuru, Creutzfeldt-Jakob disease (CJD), Gerstmann-Sträussler-Scheinker (GSS) syndrome, and fatal familial insomnia (FFI). Kuru, which was the first prion disease to be identified, in a tribe in Papua New Guinea, is thought to be transmitted through cannibalism practices. Most prion diseases have overlapping clinical features, including tremor, ataxia, involuntary movements, and dementia.
CJD is the most commonly recognized form of prion disease. The worldwide incidence is about 1 case per million population. Males and females are equally affected, and the median age of onset is 60. An iatrogenic form can occur following various surgical procedures, including corneal transplantation. Rapidly progressive mental deterioration, behavioral abnormalities, and myoclonus are characteristic of the disease. Ophthalmic disturbances are not uncommon and may include diplopia, supranuclear palsies, hallucinations, and various visual field deficits. CJD is distinguished from more common causes of dementia by its rapid onset and progression as well as the presence of myoclonus and associated gait disturbances. Brain biopsy is the gold standard in diagnosing the disorder but is rarely necessary. MRI, EEG, and cerebral spinal fluid (CSF) analysis are generally sufficient to rule out other disease etiologies and help establish the diagnosis. The presence of the CSF protein 14-3-3 is highly specific for the disease itself, but the sensitivity of the test is lower, so the usefulness of the test is limited. There is no treatment for CJD, and death often occurs within a year of onset.
Excerpted from BCSC 2020-2021 series: Section 1 - Update on General Medicine. For more information and to purchase the entire series, please visit https://www.aao.org/bcsc.