Untitled Quiz

Polioencephalomalacia (CCN)

• Affects sheep and cattle
• Characterized by malacia of the gray matter, particularly the cerebral cortex
• Caused by thiamine deficiency
• Gross lesions include discoloration, separation between gray and white matter
• Histological findings include extensive neuronal degeneration and necrosis, hemorrhage, astrogliosis, and microgliosis

Toxic Diseases

• Lead Poisoning:
  • Diffuse cerebral edema
  • Non-specific CNS lesions
  • Intranuclear inclusions in renal tubule epithelium
• Focal Symmetrical Encephalomalacia (FSE):
  • Caused by enterotoxaemia due to Clostridium perfringens type D
  • Necrosis and hemorrhage
• Hepatic Encephalopathy:
  • Secondary to liver damage
  • High levels of ammonia and amines
  • Astrocytosis

Neoplasia

• Primary tumors are rare and seldom metastasize
• Effects of neoplasia:
  • Tissue destruction
  • Space-occupying lesions
• Astrocytoma:
  • Commonly found in brachycephalic dogs
  • Located on cerebral hemispheres
  • Solitary mass
• Anencephaly:
  • Caused by genetic derangements, nutritional deficiencies, or infections

Myelination

• Primary Demyelination: Involves intact axons with damaged oligodendrocytes
• Secondary Demyelination: Necrosis of axons with intact oligodendrocytes and damaged neurons

Traumatic Injuries

• Space-Occupying Lesions:
  • Skull fracture
  • Laceration
  • Contusion
  • Haematoma (haematocyst)
    • Epidural
    • Subdural
• Routes of Spread:
  • Haematogenous
  • Adjacent structures
  • Trauma/surgery (open wounds, penetrating wounds)
  • Neural spread (viral travel via nerve)

Infectious Disease

• Meningitis:
  • Bacterial: Suppurative/purulent meningitis (e.g., Streptococcus meningitis in pigs)
  • Viral:
    • Viral Encephalitides Features:
      • Inclusion bodies:
        • Single (e.g., herpesvirus)
        • Multiple (e.g., rhabdovirus, canine distemper)
        • Intranuclear/intracytoplasmic/both
      • Perivascular cuffing (PVC):
        • Occurs in Virchow-Robins space/perivascular space
        • Non-specific to viruses but indicative of viral infection
        • Usually mononuclear cells, rarely neutrophils
    • Vasculo-endothelial changes:
      • Degeneration and necrosis of endothelium
      • Necrosis of blood vessels (fibrinoid)
    • Neuronal necrosis: Neuronophagia by microglial cells (Gitter cells)
    • Glial proliferation: Astrocytic and microglial cell response
    • Demyelination:
      • In white matter (secondary to oligodendrocyte damage)
      • In gray matter (caused by prions, as seen in bovine spongiform encephalopathy (BSE))

Rabies

• Emerging infectious disease
• Affects all mammals
• Lyssavirus from the Rhabdoviridae family, Mononegavirales order
• Vaccine options: Human diploid cell vaccine (HDCV), Purified chick embryo cell vaccine (PCEC), Rabies Vaccine Adsorbed (RVA), Rabies Immune Globulin (RIG)
• Reservoir: Megachiroptera (fruit-eating bats), Microchiroptera (insectivorous, frugivorous bats)
• Furious rabies: Characterized by fever, irritability, restlessness, anxiety, muscle pain, salivation, vomiting, painful muscle spasms (hydrophobia, aerophobia)
• Dumb rabies: Similar to furious rabies but progresses into paralysis and death
• Diagnosis:
  • History of being bitten (animal, severity, site of bite)
  • Animal:
    • If survives >10 days, not rabies
    • If dead, send brain to lab for Negri bodies, IFA, virus isolation
    • Dogs: ovaline hippocampus
    • Other species: cerebellum, spinal cord, trigeminal ganglia
  • Human:
    • Difficult to diagnose early stage of infection
    • Clinical picture, skin biopsy, corneal impression
  • Immunofluorescence, immunohistochemistry, Sellers stain
• Laboratory Tests:
  • Inclusion bodies (carmine red cytoplasm, paranuclear)
  • Brush border slide/smear of bladder transitional epithelium (Dif-Quick stain)

Canine Distemper

• Also known as "Barking Pig Syndrome"
• Natural host: Fruit bats (Pteropus sp)
• Incubation period in pigs: 4-14 days
• Clinical signs:
  • Neurological:
    • Encephalitis
    • Head pressing, agitation/biting bars
    • Tetanic spasms, seizures
    • Hind limb lameness
  • Respiratory:
    • Harsh, non-productive cough (“barking”)
    • Rapid, forced, open-mouthed respiration
• Gross Pathology:
  • Lungs: edema, pneumonia, hemorrhage, thickened septa
  • Brain (at obex): Congestion in small vessels, perivascular cuffing, vasculitis
• Histopathology:
  • Vasculitis: syncytial cells, cytolysis, necrosis
  • Immunohistochemistry indicates lung involvement

Nipah Virus Encephalitis

• Prion properties:
  • Small size (20-30 nm)
  • No nucleic acid
  • Extremely resistant to inactivation (UV, formaldehyde, heat)
  • Transmissible via intracerebral, subcutaneous inoculation of infected brain tissue
• Clinical Signs:
  • Apprehension
  • Low head carriage
  • Arched back
  • Wide-based stance

Transmissible Spongiform Encephalopathy (TSE)

• Transmissible neurological syndromes
• Novel infectious particles (prions)
• Affect humans and other animals
• Characteristics:
  • Confined to central nervous system (CNS)
  • Long incubation period
  • Progressive, uniformly fatal course
  • Brain histology:
    • Reactive gliosis
    • Vacuolation of neurons
    • Deposition of amyloid protein
    • Absence of inflammatory response
• Examples:
  • Bovine spongiform encephalopathy (BSE)
  • Scrapie (goats and sheep)
  • Feline spongiform encephalopathy (FSE)
  • Creutzfeldt-Jakob disease (human)
  • Spongiform encephalopathy (primate)

Nutritional Diseases

• Thiamine Deficiency:
  • Thiamine is an essential component in energy metabolism
  • Deficiencies lead to impaired pyruvate utilization (increased plasma pyruvate levels, ATP shortage)
  • Lesions:
    • Bilateral symmetrical
    • Edema, hemorrhage, necrosis
    • Gliosis
• Vitamin E/Selenium Deficiency:
  • Affects young animals
  • Causes white matter lesions, neuronal necrosis, gliosis

Fundamentals

• Blood Brain Barrier
  • Protection around the central nervous system (CNS), similar to a membrane
  • Newborns have a less developed BBB compared to adults
  • Degenerates with age
  • 7 areas without BBB
    • Pituitary gland
    • Median eminence
    • Area postrema
    • Preoptic recess
    • Paraphysis
    • Pineal gland
    • Endothelium of choroid plexus
• Identifying Abnormalities
  • 8 criteria for identification of abnormalities
• Classification of Lesions
  • 10 groups for classification of lesions
• Differential Diagnosis
  • Process involves considering different possible causes (aetiological) and appearances (morphological)
  • Diagnosis achieved through a process of confirmation or elimination.
• Final Diagnosis
  • Made after considering the presence or absence of abnormalities, their location, and conducting a differential diagnosis.

Similarities between Nervous System and Other Body Systems

• Neurones are surrounded by a membrane
• Neurones contain a nucleus that carries genes
• Neurones have a cytoplasm filled with mitochondria and other organelles

Differences between Nervous System and Other Body Systems

• Specialized projections: dendrites and axons
  • Dendrites carry information to the cell body
  • Axons carry information away from the cell body
• Communication between neurones occurs through an electrochemical process.
• Form specialized connections called "synapses" that release special chemicals called "neurotransmitters".
• The brain lacks lymphatics
  • Advantage: limits infection from lymphatics
  • Disadvantage: difficulty draining fluid in edema cases
• Resident macrophages within the brain are called microglials.
• Brain tissue is more susceptible to liquefactive necrosis (especially in brain)

Neuropathology

• Comprised of nerve cells (neurons) and supporting cells (glial cells).
• The brain and spinal cord are enclosed in a bony box (non-expandable) -- any lesion that occupies space in the CNS can cause problems.
  • Even a benign tumor is dangerous
• The CNS is covered by the meninges: 3 membranes that provide protection and nourish the CNS
  • Dura mater (aka pachymeninges) -- limits infection.
  • Arachnoid mater
    • Pia mater + Arachnoid mater = leptomeninges
    • Subarachnoid space (contains cerebrospinal fluid) is located between the arachnoid mater & pia mater
    • Leptomeningitis: inflammation of both meninges
  • Pia mater
    • Blood vessels connecting to CNS provide nourishment

Cranial Nerves

• I Olfactory - Smell
• II Ocular (Optic) - Vision
• III Oculomotor - Control of eye movement
• IV Trochlear - Control of eye movement
• V Trigeminal - Face sensation, mastication (chewing)
• VI Abducens - Control of eye movement
• VII Facial - Facial expression
• VIII Vestibulocochlear (Acoustic) - Vestibular (balance), Cochlear (hearing)
• IX Glossopharyngeal - Oral sensation, taste, salivation
• X Vagus - Involuntary nervous system (maintains heart rate, digestion)
• XI Accessory (Spinal Accessory) - Shoulder elevation, head turning
• XII Hypoglossal - Tongue movement

Brain

• Frontal lobe - Decision making, Memory
• Parietal lobe - Sensation (feeling)
• Occipital lobe - Vision
• Temporal lobe - Hearing (language, speech)
• Olfactory lobe - Smell
• Clinical problems are dependent on the location of the lesion
  • A tiny lesion in an "eloquent" area may present striking clinical problems
  • A large infarct in a "silent" area may be missed
  • Diverse lesions (infarcts, abscesses, tumors) in one site may produce similar problems, while similar pathologic processes at different sites will present different pictures.
• Contralateral problems : Cortical lesions produce contralateral visual, tactile, and motor problems.
• Consequences of lesions
  • Cerebellum is mostly responsible for coordination
  • Basal ganglia responsible for muscle tone
  • Consciousness is lost with damage to the pontine and midbrain reticular formation
• Selective vulnerability of cells
  • Alzheimer's affects hippocampus and cholinergic nucleus of Meynert.
  • Mercury (Hg) selectively damages cerebellar granular neurons.
  • Methanol poisons the retina.
  • Poliomyelitis destroys only the anterior horn cells.

Region of Diagnostic Tests for Emerging Viral Diseases

• Bovine Spongiform Encephalopathy (BSE) - Obex
• Canine Distemper - Demyelination in the cerebellum
• Rabies - Hippocampus
• Nipah Virus - Any part of the brain

Gliosis

• Gliosis : Proliferation or hypertrophy of glial cells
• Astrocytes :
  • Usually secondary (arising from an underlying condition)
  • Increase in ammonia toxicity
  • Decrease in necrosis
  • Unprofessional phagocytes
  • Gemistocytes (hypertrophy of astrocytes)
  • Astrogliosis (proliferation of astrocytes)

Normal Cerebrospinal Fluid (CSF) Physiology

• Produced by the choroid plexus and the brain parenchyma.
• Lateral ventricle
  • Flows through the foramen of Monroe
  • Third ventricle
  • Flows through the aqueduct of Sylvius
  • Fourth ventricle
  • Flows through the foramina of Magendie and Luschka.
• Subarachnoid space
• CSF is ultimately absorbed by arachnoid villi and through open channels around cranial & spinal nerves

Congenital Anomalies

• Emerging Diseases in Malaysia
  • Ebola
  • Rabies
  • Canine distemper
  • Nipah Virus
  • Mononegavirales

Spinal Cord & Peripheral Nerves

• Not discussed in this document.

Immature Nervous System

• Not discussed in this document.