Central nervous system infections, demyelinating disorders and prion diseases Flashcards
4 CNS infection pathways
- hematogenous, by way of respiratory mucosa, lung and other tissues (ex. skin).
- Nerves
- Direct access/wound
- Unknown
3 types of infectious diseases of the central nervous system
- meningitis: BACTERIAL, granulomatous, viral
- Encephalitis: bacterial, granulomatous, VIRAL
* *these two are highly related**
(3. cerebral abscess), focal infection
Meningitis
usually refers to inflammation of the pia and arachnoid (leptomeninges). inflammation of the dura (pachymeninges) is arare and tends to follow traumatic injury to the skull. Three types: 1. pyogenic meningitis -- bacterial 2. granulomatous meningitis -- fungal/TB 3. lymphocytic meningitis -- viral
Bacterial leptomeningitis features
common features:
- sudden onset with FEVER, severe headaches, a stiff neck, clouding of consciousness and, if untreated, often coma and death.
- a thick yellow, fibrino-purulent exudate over the convexity, or the base of the brain or both.
- congestion of meningeal vessels, spreading of the inflammatory cells (polymorphonuclear leukocytes/neutrophils) along penetrating vessels into the brain tissue and brain edema.
The three-fold importance of CSF
- constitutes a nourishing medium for the invading organisms
- helps to circulate the organisms around the brain surface and down into the spinal meninges
- when withdrawn by lumbar puncture, the fluid yields inflammatory cells and bacteria, permitting the correct diagnosis from microscopy and cultures.
Infectious organisms and age in meningitis
- Neonates/prenatal period: E. Coli., B streptococci.
- Infants and children: haemophilus influenza
- Adolescents and young adults: Neisseria meningitis (meningococcus)
- Adults: Streptococcus pneumoniae (pneumococcus), listeria monocytogenes.
CSF change in meningitis
protein +
pressure +
glucose -
PMNs +
Microscopic presentation of meningitis
- purulent bacterial leptominingitis presents yellow green pus in the subarachnoid space of the neonatal brain.
- foci of necrosis and hemorrhage in the brain. thickened leptomeninges due to inflammation.
- Intense inflammatory cells infiltrate in leptomeninges/subarachnoid space.
viral encephalitis
In acute viral inflammation of the nervous system, the tissue is congested and edematous and the cellular reaction consists chiefly of lymphocytes, macrophages, microglial cells and astrocytes.
No pus
virus RNA/DNA reaches CNS through blood stream or peripheral nerves (rabies).
around dying nerve cells “glial nodules” form which are a microscopic accumulation of lymphocytes and microglial cells and are a hallmark of viral infections.
Poliomyelitis
attack anterior horn cells and bulbar motor nuclei (in upper spinal cord??)
polio virus reaches the CNS by viremia or by axonal spread. this is an enteric (from gut) virus and it attacks and kills motor neurons, chiefly of the spinal anterior horns, but also of the cranial nerve nuclei of the medulla oblongata. respiratory paralysis can be the immediate cause of death. survivors have residual paralysis and develop secondary muscle atrophy.
Rabies
affect the deep grey matter at brainstem and cerebellum
some neurons, especially of the hippocampus, reveal cytoplasmic viral inclusion bodies, called NEGRI BODIES. treatment should start before the CNS symptoms begin.
transmitted through the saliva in the bite of a rabid animal. The virus reaches the CNS through PERIPHERAL NERVES. the incubation time is about 4-6 weeks.
Neurologic deficits appear acutely and include confusion, hyper irritability, pharyngeal spasms leading to HYDROPHOBIA, flaccid paralyses, and coma.
Herpes (HSV-1)
Temporal lobe softened with some hemorrhages
gain access to human brain through olfactory (nose) route and produce sporadic subacute encephalitis.
75% mortality if untreated. 20% after treatment with acyclovir.
can be diagnosed from the presence of HSV-1 DNA in the cerebro-spinal fluid in euro-imaging studies.
can be mistaken for an acute infarction.
arthropod-borne viruses
attacks nerve cells of the cerebral cortex, the basal nuclei and the brainstem
host in mosquito or tick vectors.
california virus/la crosse virus.
irritability, confusion, somnolence, and even stupor or coma.
no specific treatment.
HIV-1
inflammatory infiltrates are located in the white matter, in the deep grey matter and brainstem
associated edema in the white matter, myelin deficiency, and astrogliosis.
** most conspicuous feature is perivascular multinucleated giant macrophages which contain HIV-1 particles**
mostly opportunistic infections, increasing # of brain invasion via blood stream of AIDS, HIV-1 itself. brain atrophy
Demyelinating diseases of the CNS
Multiple sclerosis is the most important and the most frequent demyelinating disease.
