Transmissible Spongiform Encephalopathies

Epidemiology and Etiology

Epidemiology

Spongiform encephalopathies are extremely rare.

Known human diseases:

• Creutzfeldt-Jakob Disease (CJD)
• Kuru
• Fatal familial insomnia Insomnia Insomnia is a sleep disorder characterized by difficulty in the initiation, maintenance, and consolidation of sleep, leading to impairment of function. Patients may exhibit symptoms such as difficulty falling asleep, disrupted sleep, trouble going back to sleep, early awakenings, and feeling tired upon waking. Insomnia (FFI)
• Gerstmann-Straussler syndrome (GSS) ( incidence Incidence The number of new cases of a given disease during a given period in a specified population. It also is used for the rate at which new events occur in a defined population. It is differentiated from prevalence, which refers to all cases in the population at a given time. Measures of Disease Frequency: 1 per 100 million new cases per year)

The most common spongiform encephalopathy Encephalopathy Hyper-IgM Syndrome is Creutzfeldt-Jakob disease. The variations are:

1. Sporadic Sporadic Selective IgA Deficiency Creutzfeldt-Jakob disease (sCJD):
   • Incidence Incidence The number of new cases of a given disease during a given period in a specified population. It also is used for the rate at which new events occur in a defined population. It is differentiated from prevalence, which refers to all cases in the population at a given time. Measures of Disease Frequency: 1 per 1,000,000 cases per year (90% of cases)
   • Mean age of onset is 62 years of age
2. Variant Creutzfeldt-Jakob disease (vCJD) and iatrogenic Iatrogenic Any adverse condition in a patient occurring as the result of treatment by a physician, surgeon, or other health professional, especially infections acquired by a patient during the course of treatment. Anterior Cord Syndrome Creutzfeldt-Jakob disease (iCJD): younger age of onset (not clearly defined)
3. Genetic Creutzfeldt-Jakob disease (gCJD): clusters exist in North Africa, Israel, and Italy

Etiology

High-risk factors are:

• Cannibalism (Kuru)
• Family history Family History Adult Health Maintenance of gCJD, GSS, or FFI

Pathophysiology

Prion diseases occur when a normal, ⍺-helical protein known as PrPc is converted into an abnormal, β-pleated protein known as PrPsc. 

• Can be thought of as a “protein-misfolding” disease
• Abnormal PrP PRP Raynaud’s Phenomenon^sc is resistant to protease Protease Enzyme of the human immunodeficiency virus that is required for post-translational cleavage of gag and gag-pol precursor polyproteins into functional products needed for viral assembly. HIV protease is an aspartic protease encoded by the amino terminus of the pol gene. HIV Infection and AIDS degradation, which facilitates conversion of PrP PRP Raynaud’s Phenomenon^c into abnormal PrP PRP Raynaud’s Phenomenon^sc. This constant conversion slowly replaces normal proteins Proteins Linear polypeptides that are synthesized on ribosomes and may be further modified, crosslinked, cleaved, or assembled into complex proteins with several subunits. The specific sequence of amino acids determines the shape the polypeptide will take, during protein folding, and the function of the protein. Energy Homeostasis.
• PrP PRP Raynaud’s Phenomenon^sc accumulates in lymphoreticular and secretory organs
  • Spreads to the central nervous system Central nervous system The main information-processing organs of the nervous system, consisting of the brain, spinal cord, and meninges. Nervous System: Anatomy, Structure, and Classification (CNS) → astrocytosis → loss of neurons Neurons The basic cellular units of nervous tissue. Each neuron consists of a body, an axon, and dendrites. Their purpose is to receive, conduct, and transmit impulses in the nervous system. Nervous System: Histology → vacuolation of the brain Brain The part of central nervous system that is contained within the skull (cranium). Arising from the neural tube, the embryonic brain is comprised of three major parts including prosencephalon (the forebrain); mesencephalon (the midbrain); and rhombencephalon (the hindbrain). The developed brain consists of cerebrum; cerebellum; and other structures in the brain stem. Nervous System: Anatomy, Structure, and Classification 
  • This process causes the classic symptoms of spongiform encephalopathy Encephalopathy Hyper-IgM Syndrome:
    • Cerebellar ataxia Cerebellar ataxia Incoordination of voluntary movements that occur as a manifestation of cerebellar diseases. Characteristic features include a tendency for limb movements to overshoot or undershoot a target (dysmetria), a tremor that occurs during attempted movements (intention tremor), impaired force and rhythm of diadochokinesis (rapidly alternating movements), and gait ataxia. Cerebellar Disorders
    • Dementia Dementia Major neurocognitive disorders (NCD), also known as dementia, are a group of diseases characterized by decline in a person’s memory and executive function. These disorders are progressive and persistent diseases that are the leading cause of disability among elderly people worldwide. Major Neurocognitive Disorders
    • Death

Transmission

There are 3 primary ways of developing spongiform encephalopathies:

1. Acquired or infectious: 
   • Direct exposure to CNS-infected tissues, such as in a corneal transplant (iCJD)
   • Administration of cadaveric human pituitary Pituitary A small, unpaired gland situated in the sella turcica. It is connected to the hypothalamus by a short stalk which is called the infundibulum. Hormones: Overview and Types hormones Hormones Hormones are messenger molecules that are synthesized in one part of the body and move through the bloodstream to exert specific regulatory effects on another part of the body. Hormones play critical roles in coordinating cellular activities throughout the body in response to the constant changes in both the internal and external environments. Hormones: Overview and Types (iCJD)
   • Ingestion of food contaminated by bovine spongiform encephalopathy Encephalopathy Hyper-IgM Syndrome (BSE)-infected (“mad cow”) animal products (vCJD)
   • Cannibalism of CNS-infected tissues (Kuru)
2. Genetics Genetics Genetics is the study of genes and their functions and behaviors. Basic Terms of Genetics:
   • Mutation Mutation Genetic mutations are errors in DNA that can cause protein misfolding and dysfunction. There are various types of mutations, including chromosomal, point, frameshift, and expansion mutations. Types of Mutations from parental PrP PRP Raynaud’s Phenomenon^c into abnormal PrP PRP Raynaud’s Phenomenon^sc (gCJD, FFI, GSS)
3. Spontaneous: 
   • Sudden misfolding of PrP PRP Raynaud’s Phenomenon^c into abnormal PrP PRP Raynaud’s Phenomenon^sc (sCJD)

Clinical Presentation and Diagnosis

Transmissible spongiform encephalopathies are associated with extremely long incubation Incubation The amount time between exposure to an infectious agent and becoming symptomatic. Rabies Virus times (20–50 years) and once symptoms appear, the disease rapidly progresses to death.

No curative measures exist and the diseases are universally fatal.

Differential Diagnosis

Differential diagnosis includes diseases that are associated with rapidly progressing dementia Dementia Major neurocognitive disorders (NCD), also known as dementia, are a group of diseases characterized by decline in a person’s memory and executive function. These disorders are progressive and persistent diseases that are the leading cause of disability among elderly people worldwide. Major Neurocognitive Disorders, including the following:

• Dementia Dementia Major neurocognitive disorders (NCD), also known as dementia, are a group of diseases characterized by decline in a person’s memory and executive function. These disorders are progressive and persistent diseases that are the leading cause of disability among elderly people worldwide. Major Neurocognitive Disorders with Lewy bodies Lewy bodies Intracytoplasmic, eosinophilic, round to elongated inclusions found in vacuoles of injured or fragmented neurons. The presence of lewy bodies is the histological marker of the degenerative changes in lewy body disease and parkinson disease but they may be seen in other neurological conditions. They are typically found in the substantia nigra and locus coeruleus but they are also seen in the basal forebrain, hypothalamic nuclei, and neocortex. Parkinson’s Disease:
  • Can be rapidly progressing
  • Associated with dementia Dementia Major neurocognitive disorders (NCD), also known as dementia, are a group of diseases characterized by decline in a person’s memory and executive function. These disorders are progressive and persistent diseases that are the leading cause of disability among elderly people worldwide. Major Neurocognitive Disorders, visual hallucinations Hallucinations Subjectively experienced sensations in the absence of an appropriate stimulus, but which are regarded by the individual as real. They may be of organic origin or associated with mental disorders. Schizophrenia, and syncope Syncope Syncope is a short-term loss of consciousness and loss of postural stability followed by spontaneous return of consciousness to the previous neurologic baseline without the need for resuscitation. The condition is caused by transient interruption of cerebral blood flow that may be benign or related to a underlying life-threatening condition. Syncope
  • Histologic findings: intracellular Lewy bodies Lewy bodies Intracytoplasmic, eosinophilic, round to elongated inclusions found in vacuoles of injured or fragmented neurons. The presence of lewy bodies is the histological marker of the degenerative changes in lewy body disease and parkinson disease but they may be seen in other neurological conditions. They are typically found in the substantia nigra and locus coeruleus but they are also seen in the basal forebrain, hypothalamic nuclei, and neocortex. Parkinson’s Disease (⍺-synuclein)
• Frontotemporal dementia Dementia Major neurocognitive disorders (NCD), also known as dementia, are a group of diseases characterized by decline in a person’s memory and executive function. These disorders are progressive and persistent diseases that are the leading cause of disability among elderly people worldwide. Major Neurocognitive Disorders (Pick’s disease):
  • Associated with early changes in personality and behavior that progress to parkinsonism-like movement
  • MRI: frontotemporal lobe degeneration
• Vascular dementia Dementia Major neurocognitive disorders (NCD), also known as dementia, are a group of diseases characterized by decline in a person’s memory and executive function. These disorders are progressive and persistent diseases that are the leading cause of disability among elderly people worldwide. Major Neurocognitive Disorders:
  • Generally stepwise decline in neurological function with late-onset memory Memory Complex mental function having four distinct phases: (1) memorizing or learning, (2) retention, (3) recall, and (4) recognition. Clinically, it is usually subdivided into immediate, recent, and remote memory. Psychiatric Assessment impairment
  • MRI: multiple cortical infarctions
• Alzheimer’s disease:
  • Most common cause of dementia Dementia Major neurocognitive disorders (NCD), also known as dementia, are a group of diseases characterized by decline in a person’s memory and executive function. These disorders are progressive and persistent diseases that are the leading cause of disability among elderly people worldwide. Major Neurocognitive Disorders in the elderly
  • Symptoms often develop gradually
  • MRI: cortical and hippocampal atrophy Atrophy Decrease in the size of a cell, tissue, organ, or multiple organs, associated with a variety of pathological conditions such as abnormal cellular changes, ischemia, malnutrition, or hormonal changes. Cellular Adaptation