6.7.2 CNS INFECTIONS 6.7.2 CNS INFECTIONS Dr. Tilbe
Dr. Tilbe
FORMS OF CNS
FORMS OF CNS INFECTIONS
INFECTIONS
A. Meningitis A. Meningitis
Infection Infection limited limited to to subarachnoid subarachnoid spacespace (leptomeningitis)
(leptomeningitis)
Or spread into the brain (meningoencephalitis)Or spread into the brain (meningoencephalitis) B. Encephalitis
B. Encephalitis
Inflammation of brain; most often due toInflammation of brain; most often due to virusvirus
Maybe diffuse (entire brain involved) or localized to aMaybe diffuse (entire brain involved) or localized to a part of the brain
part of the brain C. Brain Abscess
C. Brain Abscess
Localized purulent infection of the brainLocalized purulent infection of the brain
Typically caused byTypically caused by bacteriabacteria
Maybe solitary or multiple ( usually in sepsis )Maybe solitary or multiple ( usually in sepsis )
MENINGITIS
MENINGITIS
Maybe acute or chronicMaybe acute or chronic Maybe purulent or serous (lymphocytic or aseptic) basedMaybe purulent or serous (lymphocytic or aseptic) based on CSF findings
on CSF findings
Maybe infectious or non infectiousMaybe infectious or non infectious
Types of infectious meningitisTypes of infectious meningitis::
o
o Acute pyogenic (bacterial) meningitis,Acute pyogenic (bacterial) meningitis, o
o Aseptic (usually acute viral meningitis)Aseptic (usually acute viral meningitis) o
o Chronic (usually tuberculous, spirochetal, orChronic (usually tuberculous, spirochetal, or
cryptococcal) cryptococcal)
ACUTE BACTERIAL MENINGITIS
ACUTE BACTERIAL MENINGITIS
Route of Infection Route of Infection
o
o Hematogenous dissemination (More Common)Hematogenous dissemination (More Common) o
o Direct extension(sinusitis, mastoiditis, brain abscess,Direct extension(sinusitis, mastoiditis, brain abscess,
penetrating injury, congenital defect) penetrating injury, congenital defect)
o
o Cranial bone fracture due to traumaCranial bone fracture due to trauma o
o During surgeryDuring surgery
Etiology Etiology
o
o Neisseria meningitidis (most common in children)Neisseria meningitidis (most common in children) o
o Streptococcus pneumoniae (most common in adults)Streptococcus pneumoniae (most common in adults) o
o Hemophilus influenzae (children)Hemophilus influenzae (children) o
o Gram (-) bacteria ( E coli, Klebsiella, Enterobacter) inGram (-) bacteria ( E coli, Klebsiella, Enterobacter) in
immunosuppressed following trauma or brain surgery immunosuppressed following trauma or brain surgery
o
o E coli and group B streptococcus in neonatesE coli and group B streptococcus in neonates
Age Prevalence Age Prevalence
o
o Neonates:Neonates: Escherichia coliEscherichia coli and and the group the group B B streptococcistreptococci o
o Newborn and Newborn and Elderly: Elderly: Streptococcus pnStreptococcus pneumoniae andeumoniae and
Listeria monocytogenes. Listeria monocytogenes.
o
o Infants :Infants : S. pneumoniaeS. pneumoniae o
o Adolescents Adolescents and and in in young young adults: adults: NeisseriaNeisseria
meningitides meningitides
Pathogenesis Pathogenesis
Diagnosis
Diagnosis:: CSF EXAMINATIONCSF EXAMINATION (Cornerstone) (Cornerstone)
o
o Cloudy or frankly purulent CSFCloudy or frankly purulent CSF o
o Abundant Abundant neutrophils neutrophils ( ( as as high high as as 90,00090,000
neutrophils/mm3) neutrophils/mm3)
o
o Elevated protein levelElevated protein level o
o Organisms are abundantOrganisms are abundant o
o Markedly reduced glucose content (used up byMarkedly reduced glucose content (used up by
neutrophils) neutrophils) Morphology Morphology
o
o Exudate is within the leptomeninges over the surface ofExudate is within the leptomeninges over the surface of
the brain. the brain.
o
o The location of the exudate:The location of the exudate:
H. influenzae meningitisH. influenzae meningitis: usually basal: usually basal
Pneumococcal meningitis:Pneumococcal meningitis: cerebral cerebral convexitiesconvexities near the sagittal sinus.
near the sagittal sinus.
Figure 1.
Figure 1. Purulent exudate covers the cerebral hPurulent exudate covers the cerebral hemispheresemispheres
Goes into the blood
Goes into the blood stream and enter the Subarachnoidstream and enter the Subarachnoid space
space
The organisms that cause bacterial Meningitis colonize The organisms that cause bacterial Meningitis colonize thethe
nasopharynx. nasopharynx.
Lysed granulocytes and monocytes release lysosomal Lysed granulocytes and monocytes release lysosomal enzymes and free radicals (destroy neural tissue and enzymes and free radicals (destroy neural tissue and damage blood vessels). Polyunsaturated fatty acids damage blood vessels). Polyunsaturated fatty acids released from the membranes of dying neutrophils also released from the membranes of dying neutrophils also caus
cause e increasincreased ed vascvascular ular ermeabermeabilitilit ..
Increased permeability (cerebral edema) Increased permeability (cerebral edema)
Vasculitis (ischemia) Vasculitis (ischemia) S
See ssi si sDeath Death from from ram-nram-nee ativativee shock shock
When bacteria die, lipids and oligosaccharides, including When bacteria die, lipids and oligosaccharides, including endotoxin, are released from their walls (
endotoxin, are released from their walls (SEPSISSEPSIS)) attracting circulating granulocytes and monocytes into the attracting circulating granulocytes and monocytes into the CSF and cause vascular injury.
Figure 2. Exudates settle along the base of the brain, around cranial nerves, and the openings of the fourth ventricle.
Figure 3. Neutrophilic exudation of the subarachnoid space
CHRONIC MENINGITIS
Onset: Insidious Duration: Weeks to Months Seen in: o Tuberculosis o Fungal Disease o Syphilis SourcesA. TB : Ruptured tubercles into the CSF or hematogenous dissemination
B. Fungal and Cryptococcal: hematogenous spread from lungs
C. Syphilis: manifestation of tertiary stage of syphilis.
A. TUBERCULOUS MENINGOENCEPHALITIS
Morphology: Macroscopic
Subarachnoid space contains gelatinous or fibrinous grayish-white exudates.
Often found at the base of the brain obliterating the cisterns and casing the cranial nerves.
Most common pattern of involvement: Diffuse Meningoencephalitis
Figure 4: Tuberculous exudates at the base of the brain Morphology: Microscopy
o Caseating granuloma
o Mild cases: lymphocytes, plasma cells, and
macrophages.
o Florid cases: well-formed granulomas, often with
central caseous necrosis and giant cells.
Figure 5. Epithelioid cell granulomas with Langhans giant cells, lymphocytic infiltrates, and central caseous necrosi s. Clinical Features:
o Symptoms of headache, malaise, mental confusion,
and vomiting.
o Moderate CSF pleocytosis and elevated protein
concentration
o Most serious complications:
Arachnoid Fibrosis producing hydrocephalus
Obliterative Endarteritis producing arterial occlusion and infarction
B. FUNGAL MENINGOENCEPHALITIS
primarily seen in immunocompromised patients
most common fungi involved:
Candida albicans
Mucor
Aspergillus fumigates
Cryptococcus neoformans
hematogenous dissemination
composed of three main patterns of fungal infection in the CNS:
chronic meningitis vasculitis
parenchymal invasion Parenchymal Invasion:
usually in the form of granulomas or abscesses
mostly encountered fungi: Candida:
a commensal fungi which rarely causes disease in normal people
infection is caused by organisms that are already present in the intestines and other location
in neonates, it is transmitted from external sources
most disseminated infections are nosocomial and the key risk factors are catheters and antibiotics
causes meningitis, multiple microabscesses or extensive brain necrosis
at first inflammation consists of neutrophils; later stage consists of epitheloid cells and giant cells
C. CRYPTOCOCCAL MENINGITIS
hematogenous spread from the lungs
an opportunistic infection commonly seen in immunocompromised
occurs as chronic meningitis/meningoencephalitis with meningeal fibrosis hydrocephalus (due to CSF flow obstruction)
may be fulminant and fatal in as little as 2 weeks or indolent, evolving over months and years
can cause dementia and focal neurologic deficits
oval yeast about the size of a red cell, surrounded by a gelatinous capsule
present in bird droppings, vegetables, and soil
immunocompetent host: cell mediated immune reaction with lymphocytes and epitheloid cell granulomas
Morphology: Microscopy
Parenchymal lesions consist of aggregates of organisms within expanded perivascular (Virchow-Robin) spaces associated with minimal or absent inflammation or gliosis
Infiltrates consist of chronic inflammatory cells and fibroblasts admixed with cryptococci
Figure 5: cryptococci present in perivascular space
Figure 6: Brain section looks like “Swiss Cheese” due to cystic dilatation (organism grows in the subarachnoid and perivascular spaces. Presents with a gelatinous material within the subarachnoid space and small cysts wi thin the parenchyma (“Soap Bubble Appearance”)
Diagnosis
CSF analysis:
mononuclear pleocytosis
elevated protein
low glucose
mucoid encapsulated yeasts can be visualized in the CSF by India ink preparations
PAS and mucicarmine as well as silver stains (tissue sections)
antigens can be detected by latex agglutination
D. NEUROSYPHILIS
tertiary stage of syphilis infection
3 forms:
a. Meningovascular Neurosyphilis b. Paretic Neurosyphilis
c. Tabes Dorsalis
1. Meningovascular Neurosyphilis
Morphology: Involves the base of the brain and variably also the cerebral convexities and spinal leptomeninges
Meningovascular Lesions
Lymphoplasmacytic infiltrates
Intimal thickening of small and medium-size leptomeningeal and parenchymal arteries (endarteritis obliterans- Heubner arteritis).
Parenchymal Lesions
Tabes dorsalis (rot of the spinal cord): Inflammation and degeneration of dorsal roots and posterior columns
General paresis of the insane (dementia paralytica)
o Encephalitis due to invasion of the brain by
spirochetes
o Insidious but progressive loss of mental and
physical functions
o Mood alterations (including delusions of
grandeur), terminating in severe dementia 2. Paretic Neurosyphilis
Loss of neurons with proliferations of microglia, gliosis, and iron deposits (perivascularly and in the neuropil, presumably from damage to the microcirculation)
3. Tabes Dorsalis
Damage to the sensory nerves in the dorsal roots results in:
o Impaired joint position sense and resultant
ataxia (locomotor ataxia)
o Loss of pain sensation, leading to skin and
joint damage (Charcot joints)
o absence of deep tendon reflexes.
Histologic Findings
Obliterative endarteritis ( Heubner arteritis)
Perivascular inflammatory reaction rich in plasma cells and lymphocytes
Cerebral gummas (plasma cell-rich mass lesions) may occur in the meninges and extending into the cerebral parenchyma
Symptoms of Meningitis
1. fever (more than 40C (bacterial); less than 40C (viral) 2. Onset: sudden for bacterial with prodrome for viral 3. Meningeal irritation and neurologic impairment:
headache, photophobia, irritability, clouding of consciousness, neck stiffness
4. As the disease progresses, confusion, coma, and seizures develop
Signs of Meningitis
1. Kernig sign (knee pain with hip flexion)
2. Brudzinski sign ( upon flexion of neck there is spontaneous similar movement of the hips and knees 3. Increased CSF with changes in biochemical
composition of CSF
Table 1: Cerebrospinal (CSF) Findings
COMPLICATIONS OF MENINGITIS
Scarring and obstruction of CSF leading to hydrocephalus
o Organization of fibrinopurulent exudate into fibrous
tissue >>> Block the exits of the 4th ventricle
Cranial nerve injury due to constriction may lead to neurologic deficits
Destruction of brain parenchyma lead to mental deficits, sensory defects
Epilepsy
Figure 7: Vascular narrowing after meningitis
Figure 8: Postmeningitic Hydrocephalus
TB Meningitis: Epithelioid cell granulomas destroy the pia and invade the brain.
Obliterative Endarteritis: Inflammatory infiltrates in arterial walls and marked intimal thickening >> Arterial occlusion and infarction of underlying brain. Long-Standing Cases: Dense, fibrous adhesive
arachnoiditis
Tuberculoma: Tumor-like mass, single or multiple well-circumscribed intraparenchymal mass. May cause significant mass effect.
ACUTE ASEPTIC (VIRAL) MENINGITIS
Generally of viral etiology
o 70% of cases, a pathogen can be identified,
most commonly an enterovirus
Clinical Manifestations: meningeal irritation, fever, and alterations of consciousness of relatively acute onset.
o Less fulminant course: self-limiting
Usually associated with:
o encephalitis
o meningoencephalitis
Source of Infection:
o Secondary infection in the coarse of SVI
(measles, varicella, mumps)
o Primary infection which maybe
Sporadic (HSV)
Epidemic (arthropod transmitted arbovirus)
Nonspecific gross findings Microscopic findings:
o No abnormality or
o Mild to moderate infiltration of the
leptomeninges with lymphocytes. CSF:
o Lymphocytic pleocytosis, o Moderate protein elevation
o Sugar content is nearly always normal.
REVIEW: VIRUSES
Obligate intracellular organisms.
Use cellular machinery for their replication and damage or kill the cells they infect.
Additional brain damage is caused by the cell-mediated immune reaction that they elicit.
Routes of Viral Infection
o Respiratory tract (Mumps, Measles) o Gastrointestinal tract (Enteroviruses)
o By inoculation from insect bites (Arthropod-borne
viruses)
o From animal bites (Rabies)
Most viruses reach the CNS via the bloodstream. Some viruses travel to the CNS along nerves
o Herpes simplex virus(HSV) o Varicella-zoster virus (VZV) o Rabies
Some viruses have a predilection for certain groups of neurons.
o Poliomyelitis attacks anterior horn cells
o Varicella-zoster involves sensory ganglion cells
PATHOGENESIS
Parenchymal viral infection of the brain associated with meningeal inflammation = Meningoencephalitis
Simultaneous involvement of the spinal cord = Encephalomyelitis.
Viral encephalitis:
Characteristic Histologic Features:
o Perivascular and parenchymal mononuclear cell
infiltrates (lymphocytes, plasma cells, and macrophages)
o Glial cell reactions (including the formation of
microglial nodules, and neuronophagia).
Viral infection of neurons and glial cells by viruses impairs neurological function and may cause seizures, focal neurologic deficits and coma.
Early phase:
o Neutrophilic infiltration initially of lymphocytes
and macrophages.
o Infiltrates the arachnoid membrane and the brain
diffusely but are more concentrated around blood vessels.
Figure 9: Perivascular Cuffing
Viruses
Activation of T-Lymphocytes
Release of Potent Cytokines (INF-Gamma, IL-2, TNF,
Lymphotoxin)
Mobilization of Macrophages
Attack Virus assault the host
Causing severe vascular and tissue injury
Figure 10: Activated microglial cells proliferate diffusely and form clusters around small foci of necrotic brain tissue (microglial nodules). These are histological clues of viral infection
Figure 11: Activated microglial cells encircle degenerating neurons (neuronophagia). Single-cell neuronal necrosis with phagocytosis of the debris.
Certain viruses cause intranuclear and cytoplasmic inclusions.
These inclusions consist of packed viral particles and products of their replication.
Viruses that cause inclusions are
o Herpes simplex o Cytomegalovirus o Varicella-zoster o Papovaviruses o Measles
Intranuclear inclusions, e.g. herpetic infection (Cowdry body)
Cytoplasmic inclusions, e.g. rabies (Negri body)
Nuclear and cytoplasmic inclusions e.g. (cytomegalovirus)
Figure 12: Viral inclusion bodies
Direct indications of viral infection:
o Viral inclusion bodies
o Identification of viral pathogens by
ultrastructural, immunocytochemical, and molecular methods.
Presumptive indirect evidence:
o An immune-mediated disease, such as
perivenous demyelination following systemic viral infections
I. ARTHROPOD-BORNE VIRAL
ENCEPHALITIS
Arboviruses are an important cause of epidemic encephalitis
They are capable of causing serious morbidity and high mortality
All have animals hosts and mosquito vectors except for tick-borne type
Microscopic:
The encephalitides caused by various arboviruses differ in epidemiology and prognosis, but the histopathologic picture is similar, except for variations in the severity and extent of the lesions within the CNS
Lymphocytic meningoencephalitis
Perivascular cuffing (tendency for inflammatory cells to accumulate perivascularly)
Neurophagia (single-cell neuronal necrosis with phagocytosis of the debris)
Microglial nodules (small aggregates of microglial cells around foci of necrosis)
Clinical Manifestations:
Generalized neurologic deficits, such as seizures, confusion, delirium, and stupor or coma
Focal signs such as reflex asymmetry and ocular palsies
Severe Cases:
Necrotizing vasculitis with associated focal hemorrhages
Viral Encephalitis: CSF Findings
Usually colorless
Slightly elevated pressure
Initially there is a neutrophilic pleocytosis lymphocytic pleocytosis
Protein level is elevated Sugar content is normal
II. HERPES SIMPLEX VIRUS TYPE 1 (HSV-1)
ENCEPHALITIS
Most common in children and young adults 10% of the patients have a history of prior herpes
Alterations in mood, memory, and behavior (most commonly observed clinical presenting symptoms)
Location: inferior and medial regions of the temporal lobes and the orbital gyri of the frontal lobes (initial and most severely affected.
Most common year-round viral encephalitis
Most people become primarily infected with HSV in their teens or twenties
HSV type 1 is transmitted by the saliva MORPHOLOGY:
Gross: Necrotizing and often hemorrhagic
Microscopic: Cowdry type A intranuclear viral inclusion bodies in both neurons and glia
PATHOGENESIS:
Initial HSV infection stomatitis virus remains latent in the trigeminal ganglion reactivated virus can spread in the:
Skin (along the branches of the trigeminal nerve) sores on the lips (herpes labialis)
Brain infecting the meninges of the anterior and middle cranial fossae
From the meninges, HSV extends to the adjacent brain
affects the temporal and inferior frontal lobes (first and more severely) then spreads to the rest of the brain
ADULT HSV ENCEPHALITIS Limited to the brain
Symptoms: fever, confusion, coma and seizures
Involvement of the frontal and temporal lobes – bizarre behavior, personality changes, anosmia and gustatory
hallucinations
Survivors may have Korsakoff’s amnesia, dementia and seizures
Figure 13: Adult HSV encephalitis (gross) - diffuse softening and edema, hemorrhagic necrosis of the inferior frontal and temporal lobes
Microscopic findings: (1) Acute phase:
Meningeal and perivascular mononuclear cells Increased microglia
Focal necrotizing vasculitis
Eosinophilic intranuclear inclusions in glial cells and neurons
Figure 14: Intranuclear eosinophilic amorphous or droplet-like bodies surrounded by a clear halo (pointed structures)
(2) End stage:
Brain atrophy and gliosis
Brain destruction is more severe than any other viral encephalitis
CSF Findings:
Pleocytosis (early neutrophils, late lymphocytes) Elevated protein (depends on the degree of brain
necrosis)
Glucose is normal
III. HERPES SIMPLEX VIRUS TYPE 2 (HSV-2)
HSV-2 infection of the brain is usually manifested in adults as meningitis
Severe encephalitis develops in as many as 50% of neonates born by vaginal delivery to women with active primary HSV genital infections
HSV-2 may cause an acute, hemorrhagic, necrotizing encephalitis in AIDS patients
NEONATAL HSV INFECTION
70% are caused by HSV type II (herpes genitalis) Acquired during vaginal delivery
HSV transmitted across the placenta
Acquired by babies in the NB nursery or at home
Figure 15: Neonatal HSV encephalitis. (Gross) Diffuse necrotizing encephalitis. In time, the lesions evolve into cystic encephalomalacia with microcephaly.
IV. CYTOMEGALOVIRUS (CMV)
Infected pregnant mother may transmit the virus to the fetus, causing a generalized fetal CMV infection
CMV infection may develop at any stage during pregnancy and may continue after delivery
CNS infection occurs in fetuses and immunosuppressed individuals
In utero infection: periventricular necrosis severe brain destruction microcephaly with periventricular calcification
Infected neurons and glial cells enlarge and develop cytoplasmic and intranuclear inclusions
Figure 16: Cytomegaly and intranuclear inclusions
Figure 17: (Gross: Congenital CMV, cortical atrophy and calcifications) heavily infected areas become necrotic and calcify. Lesions have a predilection for the walls of the ventricles. Infection before mid-gestation may derange the process of neuronal migration, causing microcephaly and cortical dysplasia.
Cytomegalovirus Encephalitis
Rare in adults and usually occurs as part of a generalized CMV infection in i mmunocompromised patients
Most common opportunistic viral pathogen in patients with AIDS, affecting the CNS in 15-20% of cases
V. POLIOMYELITIS
Poliovirus infection causes a subclinical or mild gastroenteritis.
Secondarily invades the nervous system in vulnerable persons
Morphology
Acute cases
Mononuclear cell perivascular cuffing
neuronophagia of the anterior horn motor neurons of the spinal cord.
Postmortem examination in long-term survivors of symptomatic poliomyelitis shows loss of neurons and gliosis in the affected anterior horns of the spinal cord, some residual inflammation, atrophy of the anterior (motor) spinal roots, and neurogenic atrophy of denervated muscle.
Clinical Features.
Initial manifestation: meningeal irritation and a CSF picture of aseptic meningitis
May progress to involve the spinal cord where it causes loss of motor neurons producing flaccid paralysis with muscle wasting and hyporeflexia in the corresponding region of the body—the permanent neurologic residue
In acute disease, death can occur from paralysis of the respiratory muscles, and a myocarditis sometimes complicates the clinical course.
sis or paralysis
follows (when it involves the innervation of the compromise may occur and cause long-term morbidity) Post-polio syndrome
25 to 35 years after the resolution of the initial illness.
Progressive weakness associated with decreased muscle mass and pain
VI. RABIES
Severe encephalitis
Transmitted to humans by the bite of a rabid animal, a dog or various wild animals
Morphology Gross:
Brain shows intense edema and vascular congestion Microscopic:
Widespread neuronal degeneration
Inflammatory reaction; most severe in the brainstem (basal ganglia, spinal cord, dorsal root ganglia may also be infected)
Regions most severely affected: midbrain, floor of fourth ventricle (part in the medulla)
Figure 18: Negri bodies = Pathognomonic microscopic finding for Rabies
Cytoplasmic, round to oval, eosinophilic inclusions in pyramidal neurons of the hippocampus and Purkinje cells of the cerebellum (sites usually devoid of inflammation)
Contains rabies virus Clinical Features:
Virus enters the CNS by ascending along the peripheral nerves from the wound site
Incubation period (bet 1 and 3 months) depends on the distance between the wound and the brain
The disease begins with nonspecific symptoms (malaise, headache, fever) but the conjunction of these symptoms with local paresthesias around the wound is diagnostic.
As the infection advances, the affected individual exhibits extraordinary CNS excitability; the slightest touch is painful, with violent motor responses progressing to convulsions. Contracture of the pharyngeal musculature on swallowing produces foaming at the mouth, which may create an aversion to swallowing even water (hydrophobia).
There is meningismus , and as the disease progresses, flaccid paralysis.
Periods of alternating mania and stupor progress to coma and death from respiratory center failure.
VII. HUMAN IMMUNODEFICIENCY VIRUS
60% of patients with AIDS develop neurologicdysfunction during the course of their illness
Infects and destroys CD4 lymphocytes, causing immune deficiency
Neurologic Dysfunction due to:
Direct or indirect effects of HIV
Opportunistic infection
Primary CNS lymphoma
If there is CNS lymphoma you should rule out the possibility of immunodeficiency of whatever cause
AIDS patients are susceptible to opportunistic infections
CNS toxoplasmosis
Cryptococosis and other mycoses
CMV encephalitis
Papovavirus infections (PML)
AIDS patients develop cerebral and other extranodal B-cell lymphomas
Directly cause aseptic meningitis, encephalitis, leukoencephalopathy, myelopathy, neuropathy, and myopathy
Patterns of inflammation:
Aseptic meningitis
Encephalitis
Meningoencephalitis 1. ASEPTIC HIV 1 MENINGITIS
o occurs 1-2 weeks of seroconversion in about 10% of
patients; antibodies to HIV can be demonstrated and the virus can be isolated from the CSF
o mild lymphocytic meningitis, perivascular
lymphocytic inflammation, and some myelin loss in the hemispheres.
o Among the cell types of the CNS, only microglia have
the appropriate combination of CD4 and a chemokine receptor (CCR5 or CXCR4) to allow for the efficient infection by HIV.
o During the chronic phase, an HIV encephalitis is o commonly found when symptomatic individuals
come to autopsy.
2. HIV 1 MENINOENCEPHALITIS (SUBACUTE ENCEPHALITIS)
o Presents with AIDS-dementia complex
o Cognitive changes, both mild and florid enough to be
termed, HIV associated dementia, appear to have persisted into the era of effective anti-HIV treatment regimens.
HIV Encephalitis
Causes AIDS-dementia complex: progressive memory loss, intellectual deterioration, behavioral changes, and motor deficits
Damage to neurons and oligodendrocytes occurs indirectly through the release of toxic cytokines and alterations of the blood-brain barrier
Morphology: Gross
Meninges are clear
Ventricular dilation with sulcal widening
Normal cortical thickness Microscopic:
Diffuse myeline damage (spongy myelinopathy, gliosis)
Neuronal loss
Vascular damage
Microglial nodules
Figure 19: chronic inflammatory reaction with widely distributed infiltrates of microglial nodules, sometimes with associated foci of tissue necrosis and reactive gliosis
Figure 20: HIV envelope glycoproteins cause the membranes of HIV-infected macrophages to fuse >>> form multinucleated giant cells (Black Arrow)= hallmark of HIV encephalitis. ) Microglial nodules are also found in the vicinity of small blood vessels.
An important component of the microglial nodules the macrophage-derived multinucleated giant cell.
In some cases there is also a disorder of white matter characterized by multifocal or diffuse areas of myelin pallor, axonal swelling, and gliosis.
Congenital HIV infection
Caused when an HIV infected mother transmits the infection to the fetus
More severe than the adult form may result in microcephaly
Distinctive feature of congenital AIDS: basal ganglia calcification
Pathogenesis
Virus is carried into the brain by infected CD4 lymphocytes and perivascular monocytes
Microglial cells pick up free viral particles
The only cells that harbour HIV in the brain are perivascular monocytes and microglia
Brain damage is caused mainly by activated monocytes and microglial cells producing:
Cytokines (such as TNF)
Neurotoxins (such as glutamate and NO produced by activated monocytes and microglial cells)
VIII. SUBACUTE SCLEROSING PANENCEPHALITIS
(SSPE)
Rare
Progressive clinical syndrome characterized by cognitive decline, spasticity of limbs, and seizures.
It occurs in children or young adults, months or years after an initial, early-age acute infection with measles.
Probably due to persistent infection of the CNS by an altered measles virus
Microscopic Findings:
Widespread gliosis and myelin degeneration
Viral inclusions, largely within the nuclei of oligodendrocytes and neurons
BRAIN ABSCESS
Arise by:1. Direct extension from infection in neighborhood, e.g., middle ear-mastoid, paranasal sinuses, open wounds
2. Hematogenous , particularly from endocarditis and bronchial-pulmonary infections
Predisposing conditions:
Acute bacterial endocarditis >> multiple abscesses
Cyanotic CHD: right-to-left shunt >> pulmonary filtration of organisms is lost
Chronic pulmonary sepsis (bronchiectasis).
**
Streptococci and staphylococci: most common organisms in non-immunosuppressed CSF findings:
increased pressure;
white cell count and protein level are elevated
Sugar content is normal. Pathogenesis:
Destruction of brain tissue progressive loss of neurological function Pus and edema of surrounding tissue causes ICP to elevate Increased ICP and progressive herniation can be fatal.
Morphology:
Figure 21: (Gross) Discrete lesions with central liquefactive necrosis, a surrounding fibrous granulation tissue capsule, and edema.
I. CEREBRAL TOXOPLASMOSIS
Etiology: Toxoplasma gondii One of the most common causes of neurologic symptoms and morbidity in patients with AIDS.
Clinical symptoms are subacute, evolving during a 1- or 2-week period, and may be both focal and diffuse.
Primary maternal infection with toxoplasmosis ( early in the pregnancy) cerebritis in the fetus production of multifocal cerebral necrotizing lesions calcify
producing severe damage Morphology:
Gross: Brain shows abscesses most involving the cerebral cortex (near the gray-white junction) and deep gray nuclei
Microscopy: Acute lesions consist of central foci of necrosis with variable petechiae surrounded by acute and chronic inflammation, macrophage infiltration, and vascular proliferation