Study your flashcards anywhere!

Download the official Cram app for free >

  • Shuffle
    Toggle On
    Toggle Off
  • Alphabetize
    Toggle On
    Toggle Off
  • Front First
    Toggle On
    Toggle Off
  • Both Sides
    Toggle On
    Toggle Off
  • Read
    Toggle On
    Toggle Off
Reading...
Front

How to study your flashcards.

Right/Left arrow keys: Navigate between flashcards.right arrow keyleft arrow key

Up/Down arrow keys: Flip the card between the front and back.down keyup key

H key: Show hint (3rd side).h key

A key: Read text to speech.a key

image

Play button

image

Play button

image

Progress

1/72

Click to flip

72 Cards in this Set

  • Front
  • Back
1. Abnormal Tau deposits are found in:
A. Senile plaques
B. neurofibrillary tangles
C. Both
D. Neither
Senile plaques are made up of beta-amyloid
neurofibrillary tangles are made of tau proteins
2. The main component of neurofibrillary tangles is:
A. Tau protein
B. Ubiquitin
C. Synuclein
D. Beta amyloid
Neurofibrillay tangles are composed of tau proteins which form paired helical filaments
*3. Neurofibrillary tangles occur also in:
A. Friedreich ataxia
B. Huntington's disease
C. Creutzfeldt-Jacob disease
D. Progressive supranuclear palsy
80% of Alzheimer's Disease cases present with Neurofibrillary tangles
Huntington's disease: atrophy of caudate and putamen as well as CAG repeats on chromosome 4
Progressive supranuclear palsy presents with neurofibrillary tangles
6. The amount of beta amyloid made by cells of a patient with Down syndrome is:
A. The same as normal people
B. 1.5 times normal
C. 2 times normal
D. 3 times normal
A patient with Down Syndrome has Trisomy 21. This person has 1.5 times more amyloid protein made.. therefore a person with Down Syndrome will have Alzheimer's disease
*7. The earliest changes in Alzheimer's disease are usually found in:
A. Hippocampus
B. Entorhinal cortex
C. Amygdala
D. Association cortex
The progression of the disease is from the entorhinal cortex, then spread through the hippocampal cortex, to the amydala to the neocortex. Plaques can be found in the hippocampus and amygdala as well as in the neocortex althought there is sparing of primary motor and sensory cortex until late in the course of the disease.
8. A patient with large ventricles, dementia, incontinence, and abnormal gait should:
A . Have a brain biopsy to rule out Alzheimer's disease
B . Have a shunt placed to relieve hydrocephalus
-
an autopsy was performed and findings were
decreased brain weight
generalized cerebral atrophy
hydrocephalus ex vacuo
atrophy of hippocampus and amygdala

cause of death was probably
a. Friedreich's Ataxia
b. Amyotrophic Lateral Sclerosis
c. Alzheimer's Disease
The cause of death was Alzheimer's disease to confirm look for senile plaques that contain amyloid and NFT which contain tau proteins

Friedreich's Ataxia is a disease of the cerebellum and spinal cord so there is degeneration of the spinal cord posterior columns, SCT and to a lesser extent CST. To confirm look for heart anomalies & elelctrical conduction

ALS is a motor neuron disease with UMN and LMN symtoms. The cerebral cortex is normal but there is symmetrical atrophy of the motor cortex, discoloration of the CST and atrophy of ventral roots of spinal cord.
Which of the following is least likely to be affected in Parkinson's disease:
A. The cerebral cortex
B. The nucleus basalis of Meynert
C. The hypothalamus
D. The caudate nucleus
Parkinson's disease affects the basal ganglia
Parkinson's symptoms are causesd by lack of SN Dopamine innervation
D1 lessens inhibition of GPm leading to bradykinesia
D2 increases net stimulation of GPm leading to atonia

The caudate and putamen are affected in Huntington's disease
Parkinson's Disease and Progressive Supranuclear Palsy are similar in that they both show substantia nigral degeneration.

What are the differences between Parkinson's Disease and Progressive Supranuclear Palsy?
Progressive Supranuclear Palsy has symptoms of parkinsonism because of SN degeneration,

also has:
atrophy of Globus Pallidus which interupts the pathway to the cortex and leads to motor problems
atrophy of the subthalamic nuclei
atrophy dentate nuclei of the cerebellum atrophy

->Dentate nucleus is related to the pontocerebellum or neocerebellum which is responsible for planning and coordination of somatic motor movements both stereotyped automatic eg. walking and non-stereotyped precise, directed movement which causes gait disturbances seen in PSP

also NFT in CNIII, IV leading to ophthalmoplegia
Which of the following is not a trinucleotide repeat disorder:
A. Parkinson's disease
B. Huntington's disease
C. Friedreich's ataxia
D. Spinocerebellar Ataxis
Huntington's disease is an autosomal dominat disorder due to CAG repeats on chromosome 4.

Friedreich's ataxia is caused by GAA repeat in the first intron of the frataxin gene located on chromosome 9q13

Spinocerebellar ataxias have the CAG repeats in the huntingtin protein same as in Huntington's disease
Frataxin is located in the:
A. Mitochondria
B. Lysosomes
C. Nucleus
D. Cytosol
Frataxin is a protein that regulates mitochondrial iron levels needed for the oxidative phosphorylation chain enzymes
Which of the following is a polyglutamine disorder:
A. Friedreich's ataxia
B. Autosomal dominant spinocerebellar ataxia
C. OPCA
D. The Fragile X syndrome
Only autosomal dominant spinocerebellar ataxias are polyglutamine disorders (they encode CAG trinucleotide repeats).
Friedreich’s ataxia is associated with a GAA trinucleotide repeat.
The fragile X syndrome is associated with the CGG repeat.
Most OPCA cases are sporadic and are not associated with trinucleotide repeats.
What are the lab and clinical tests for ruling out reversible forms of dementia in the elderly?
Neuroimaging- Head CT Scan without contrast and Head MRI without contrast
Neuropsychology testing
Chemistry Survey (Electrolytes, BUN, Creatinine, Glucose)
Hematology (CBC with differential)
Vit B12 and Folate Levels
RPR (Syphilis)
T3, T4, TSH (Thyroid Function Tests)
Sedimentation Rate
What are the reversible forms of dementia?
Atherosclerosis- statins like Lipitor
Embolic Sources- Warfarin (Coumadin)
Non-Hemorrhagic Stroke-recombinant tissue plansminogen activator; streptokinase/urokinase
Hypothyroidism-synthyroid
Cushing's Syndrome- Mifepristone and other glucorticoid antagonists
Nutritional Deficiency
Drug Intoxication
Neurosyphilis (penicillin)
Brain Tumor (decadron which decreases cerebral edema)
Depression
Schizophrenia
What are the nutritional deficiencies that lead to dementia?
Nutritional Deficiency
-> Pellagra (niacin): dementia, dermatitis, diarrhea
-> Wernicke-Korsakoff syndrome (thiamine): alcoholic dementia
->Pernicious anemia (Vit B12): subacute combined degeneration
What are the theoretical drug therapies for Alzheimer's Disease?
Estrogen
NSAIDS eg indomethacin, ibuprofen, COX-2 inhibitors eg. Celebrex
Anti-oxidants-NO EFFECT
Statins
Herbal Treatments- NO EFFECT
What are the treatment strategies for symptomatic Alzheimer's disease?
Cholinomimetics
Degradation of Choline Inhibitors
Direct Cholinergic Agonists
NMDA Antagonists
Monoaminergic drugs that are selective serotonin reuptake blockers
Monoaminergic drugs that are selective serotonin reuptake blockers
fluoxetine, depression and memory
a
NMDA Antagonist is memantine (Ebixa or Axura)
a
used to treat Alzheimer's Disease which is caused in part to degeneration of cholinergic neurons in the nucleus basalis of Meynert
Benign epithelial tumors are called
adenoma
malignant epithelia tumors are called
carcinomas
malignant mesenchymal tumor is called
sarcoma
malignant brain tumor is called
glioma
Primary CNS neoplasms
most common cancer - lung
second most common in females is breast cancer and in males is colon cancer
Presentation of tumors
seizures, docal deficits, ICP, hydrocephalus, nausease vomiting
death caused by increase ICP and herniation
Where is it frequently found in adults >15yo
• Adults
– Usually Supratentorial
• Glioma (mostly astrocytoma/GBM)
• Meningioma
• Lymphoma
• Metastatic cancer
– Posterior fossa
• Schwannoma
• Meningioma
Where is it frequently found in pediatrics
• Pediatric
– Usually in the posterior fossa
• Medulloblastoma (high grade)
• Ependymoma (intermediate)
• Pilocytic astrocytoma (low grade)
– Cerebral tumors are rarer
• Optic glioma (PA, low grade)
• Ganglioglioma (low grade)
• PNET (high grade)
What is the etiology
Etiology
• Mostly unknown
• Post radiation
– usually sarcomas
– Can be glioma or nerve sheath tumor
• Virus
– EBV in lymphoma
– Papova virus can cause astrocytoma experimentally
(also causes PML)
– Other?
• Genetic factors
– SEX
• astros3:2 in men
• meningioma 2:1 women
True or False: children and adults get
similar kinds of tumors, and tumors in
similar locations?
• False:
– Children usually have infratentorial tumors like
medulloblastomas, pilocytic astrocytomas and
ependymomas;
– adults have supertentorial tumors like gliomas
(astrocytoma, oligodendroglioma),
meningiomas, and pituitary adenoma.
Pilocytic astrocytoma
hair like cells
Pilocytic astrocytoma
• WHO grade I
• Mostly kids
• Cerebellum, optic nerve,
chiasm/hypothalamus.diencephalon,
temporal lobe
• Cerebral location tend to be older patients
• Associated with NF1 (esp. optic)
‘Fibrillary’ Astrocytoma
‘Fibrillary’ Astrocytoma
• At least 1/3 of all intracranial tumors
• Cerebrum in adults and brainstem in kids
• 50% of adult astros are high grade (GBM)
• Low grade astro tends to transform to high
grade in 5 –10 years (“secondary” GBM).
Some histological findings of bening tumors
Hemociderin
Rosenthal fibers
Eosinophilic Granular Bodies
small cells and hyalinized vessels
• What features are characteristic of GBM?
• Which genetic mutations are more common in primary GBM?
• The most significant prognostic factor in astrocytomas is?
• What features are characteristic of GBM?
– Palisading necrosis
– Vascular endothelial proliferation

• Which genetic mutations are more common in primary GBM?
A) EGFR, MDM2 and PTEN; or
B) p53, RB1 and –19q?
– A

• The most significant prognostic factor in astrocytomas is?
– Age
Oligodendroglioma
Oligodendroglioma
• 7-10% of primary CNS tumors
• M:F 1:1
• 30-50 years
• Frontal lobe
• Often present with seizures
• Prone to hemorrhage
• More sensitive to chemotherapy
9. Which of the following is not a feature of pilocytic astrocytoma?
A. Granular eosinophilic droplets
B. Brisk mitotic activity
C. Drop metastases
D. Location in the spinal cord
E. Hydrocephalus
Brisk mitotic activity is not a feature of pilocytic astrocytomas. Drop metastasis have been reported with some hypothalamic pilocytic astrocytomas. PAs may be located in the spinal cord. In their most common location, the posterior fossa, they may obstruct CSF flow causing hydrocephalus. GEDs are a cellular marker of PAs.
What finding distinguishes glioblastoma multiforme from lower grade astrocytomas?
A. Mitoses
B. Cellular density
C. Necrosis
D. Marked anaplasia (giant cells)
Necrosis occurs only in GBM.
palisading necrosis
vascular endothelial proliferation
• Oligodendrogliomas are characterized by?

• A frequent genetic change in
oligodendroglioma that also indicates response to treatment is...

Genetic analysis of ‘oligoid’ tumors show...
• Oligodendrogliomas are characterized by?
– Chicken wire vessels
– Perinuclear clearing (fried egg cell)

• A frequent genetic change in
oligodendroglioma that also indicates
response to treatment is
– deletion of 1p and 19q

Genetic analysis of ‘oligoid’ tumors show
• Loss of 1p on ~80%, early event
• Loss of 19q also ~80%, strong linkage to 1p loss
• p53 mutation (17p) uncommon
Ependymoma
• 6-9% of primary CNS lesions
• Usually children (30% of pediatric primary)
• Often infratentorial
• Spinal:
– Usually myxopapillary, 20-40 years old
– Associated with NF-2
Ependymoma: Perivascualar pseudorosettes
Medulloblastoma
Medulloblastoma
• 5% of CNS neoplasms
• 20% of pediatric CNS neoplasms
– Bimodal (peaks at ~3-4 and young adult (older
more often lateral)
• 90% of pediatric ‘PNET’
• Usually arise from vermis/4th ventricle
• Patients require craniospinal radiation and
chemotherapy
– About 70% survive
Meningioma
Meningioma
• Incidence increase with age, can be asymptomatic
• 15% of intracranial, 25% intraspinal lesions
• 10% have multiple meningiomas
• Most are supratentorial
• Intracranial 3:2 F:M; intraspinal 10:1 F:M
• Associated with:
– Radiotherapy
– Estrogenic neoplasms (i.e. breast, endometrial CA)
– Castleman’s (chordoid and lymphocyte-rich var.)
– Polyclonal gammopathies (lymphocyte-rich var.)
Schwannomas
Schwannomas
• 8% of intracranial neoplasms
• 4th and 5th decade
• Vestibular portion of 8th N
– If bilateral, strongly consider NF2
• Sometimes 5th N
• Spinal are usually sensory roots, lumbosacral
• Intradural and extramedullary
Which type of vessel is associated with
malignancy?
A) hyalinized vessels;
B) vessels with endothelial proliferation;
C) vessels with perivascular pseudorosettes?
– B, as seen in GBM. Hyalinized vessels are seen in low grade tumors like pilocytic astrocytoma and schwannoma. Perivascular
pseudorosettes are seen in ependymomas.
Pituitary fossa neoplasms
Pituitary fossa neoplasms
• Most common:
– pituitary adenomas and meningioma
• Others:
– Craniopharyngioma, germ cell tumor, astrocytoma,
metastases
Pituitary adenomas
Pituitary adenomas
• Genetics: MEN 1 (pancreas, parathyroid)
• 10-15% of intracranial neoplasms
• 3rd-6th decade
• F:M 3:1, incidental prolactinomas not
uncommon
• Hormone symptoms (can also be peptide
deficiencies) or mass effects
Which of these tumors can have rosette-like
structures?
A) ependymoma
B) medulloblastoma,
C) schwannoma,
D) pituitary adenoma?
Which of these tumors can have rosette-like
structures?
A) ependymoma
B) medulloblastoma,
C) schwannoma,
D) pituitary adenoma?
– All of them can!
Metastases
Metastases
• 15% of intracranial neoplasms
• About 30% of patients with disseminated CA
will have brain mets.
• 6th-7th decade
• Solitary met about 50% of the time ?treatable
• About 50% are from lung
• Initial presentation about 15% of the time
Lung 50% of metastases
Breast 15% of CNS metastases
Melanoma- 10% of CNS metastases
Kidney- 5% of CNS metastases
Frequency of lung tumor metastasizing to the brain is 35%
Breast is 20%
Melanoma is 50%
melanomas appear somewhat brain 'trophic' and is found in the brain out of proportion to its incidence
Are there any truly benign CNS neoplasms?

What factor does age play in prognosis of brain tumor?

Name some specific mutations associated in oligos?

What percent of brain tumors are due to metastasis?

What is the most common primary CNS tumor in adults?

What is the most common primary CNS tumor in children?
• There are no truly ‘benign’ CNS neoplasms, just more or less aggressive ones
• Past childhood, age is a bad prognostic factor
• Some specific mutations are associated with tumors,
e.g. deletion of 1p and 19q in oligos.
• Metastases account for about ½ of all brain tumors
• The most common primary CNS tumors in adults are astrocytomas and meningiomas - cerebral
• In children the most common are medulloblastomas and pilocytic astrocytomas - cerebellar
Ependymomas
Ependymomas are predominantly tumors of children and adolescents.

They arise most frequently in the fourth ventricle and cause hydrocephalus by blocking CSF flow.

However, they may occur anywhere in relation to the ventricular system or central canal and are the most common primary intra-axial tumors in the spinal cord and filum terminale.

Grossly, ependymomas are well demarcated from the surrounding brain and spinal cord and grow in an exophytic fashion, protruding into and out of the fourth ventricle. Spinal ependymomas are circumscribed intra-axial masses.
Oligodendrogliomas are among the most _____________ solid tumors.

They show losses of chromosomes __ and ___ which correlate with increased ____________ and longer survival.
Oligodendrogliomas are among the most chemosensitive solid tumors.

They show losses of chromosomes 1p and 19q which correlate with increased chemosensitivity and longer survival.
What age and region of the CNS are affected by Pilocytic Astrocytoma?

How does it appear grossly and microscopically?
Pilocytic astrocytoma (PA) is a biologically and histologically distinct form of astrocytoma of children and young adults.

Most pilocytic astrocytomas arise in the cerebellum and hypothalamus. Some arise in the optic nerves and cerebral hemispheres.

Grossly, pilocytic astrocytomas are circumscribed and often cystic.

Histologically, they are sparsely cellular tumors without anaplasia or mitoses. They show a biphasic pattern, consisting of cellular and fibrillary perivascular areas, alternating with loose microcystic zones. The tumor cells often contain Rosenthal fibers and granular eosinophilic droplets
Glioblastoma multiforme (GBM) is the most _______ form of _____________.

It occurs most frequently in middle aged adults.

Its most common sites are the _______ and _______ lobes, but it may occur at any age and involve any part of the CNS.

GBM arises most commonly__________.

Some GBMs arise by malignant transformation of low-grade _______ (secondary GBM).

Primary GBMs are more _____ in older patients and are more __________.
Glioblastoma multiforme (GBM) is the most malignant form of astrocytoma. It occurs most frequently in middle aged adults. Its most common sites are the frontal and temporal lobes, but it may occur at any age and involve any part of the CNS. GBM arises most commonly de novo (primary GBM).

Some GBMs arise by malignant transformation of low-grade astrocytomas (secondary GBM).

Primary GBMs are more common in older patients and are more aggressive.
Gross examination of samples show several findings to confirm GBM. What are some of those?
On naked eye examination ,
GBM is a poorly defined mass
with variegated (multiform) appearance due to
necrosis and hemorrhage.

If the tumor is near the center of the cerebrum, it may spread from one hemisphere to the other through the

corpus callosum.
What are the major pathological findings that are microscopically indicative of GBM?
Microscopically, GBM shows
high cellularity,
cellular and nuclear anaplasia which is the basis of the designation "multiforme",
mitoses,
microvascular proliferation,
and
necrosis.
a
Compare Astrocytoma and GBM.

GBM corresponds to grade ___ and pilocytic astrocytoma to grade ___.
Astrocytoma and GBM are a continuum.
Astrocytoma: At one end of the spectrum are low-grade tumors with sparse cellularity, minimal anaplasia and no mitotic activity.

At the other end (GBM), are malignant tumors, characterized by high cellularity, anaplasia, mitoses, vascular endothelial proliferation, and necrosis.

GBM corresponds to grade IV and pilocytic astrocytoma to grade I.

Low grade astrocytomas are more frequent in children and young adults and high grade astrocytomas in older patients.
The Wernicke-Korsakoff syndrome affects all of the following except

A. The hippocampus
B. The mammillary bodies
C. The thalamus
D. The third nerve nucleus
The hippocampus is not affected in the Wernicke-Korsakoff syndrome. However, bilateral hippocampal damage can cause a memory defect (Korsakoff amnesia) similar to the WKS. The mammillary bodies, periaqueductal area, and floor of the 3rd ventricle (where the third nerve nucleus is located) are the main sites of damage.
Subacute combined degeneration is:

A. A genetic metabolic disorder
B. A demyelinative disease
C. A nutritional deficiency disorder
D. A form of motor neuron disease
E. A paraneoplastic syndrome
Subacute combined degeneration is caused by Vitamin B12 deficiency.
Korsakoff's amnesia can result from:

A. HIE-stroke.
B. Seizures.
C. Both.
D. Neither.
Both, HIE and seizures can cause bilateral hippocampal damage.
A 49 year old man had resection of the terminal ileum and part of the colon for Crohn's disease. Seven years later, tingling, weakness, and spasticity of the legs develops. He should be treated with:
A. Vitamin B12.
B. Vitamin B6.
C. Plasma exchange.
D. Vitamin B1.
He most likely had Vitamin B12 deficiency and subacute combined degeneration.
Which is more likely to develop one week after the onset of untreated bacterial meningitis?
a. Ischemic infarcts
b. Subarachnoid hemorrhage
c. Deafness
d. Hydrocephalus
e. Hypoxic-ischemic encephalopathy
increased polymorphonuclear WBC,
decreased CSF glucose
Ischemic infarcts may develop in a few days because of vasculitis. Hypoxic-ischemic encephalopathy may also develop, usually earlier. Deafness and hydrocephalus develop much later.
Which of the following is most common among the following complications of meningitis?
a. Cerebritis
b. Brain abscess
c. Ventriculitis
d. Subdural abscess
Ventriculitis is the most common of the listed complications.
The most dangerous feature of an abscess is:
a. Sepsis
b. Loss of neurological function
c. Increased intracranial pressure
d. Development of meningitis
The most life threatening feature of an abscess is cerebral edema and increased intracranial pressure.
Meningitis usually crosses the pial barrier and involves the brain
a. True
b. False
The pia is a very tough structural barrier. It is not easily trespassed and helps confine meningitis to the subarachnoid space.
What is the difference between Meningitis and Encephalitis?
Viral infection of the arachnoid membrane and CSF causes headache, stiff neck and mononuclear CSF pleocytosis with normal protein and glucose. This syndrome is called aseptic meningitis, because no bacterial organisms are isolated. The most common agents causing aseptic meningitis are enteroviruses. Involvement of neurons and glial cells by viruses (viral encephalitis) impairs neurological function and causes seizures, focal neurologic deficits, and coma. Encephalitis is accompanied by viral meningitis whereas aseptic meningitis may occur alone.
Herpes Simplex
Adult and pediatric (post-neonatal) HSV encephalitis is caused most commonly by HSV type I. It is the most common year-round viral encephalitis. Most people become primarily infected with HSV in their teens or twenties. HSV type I is transmitted by the saliva. The initial infection causes a stomatitis. Following this, the virus remains latent in the trigeminal ganglion. From this location, reactivated virus can spread either to the skin, along the branches of the trigeminal nerve, causing sores on the lips (herpes labialis), or to the brain, infecting the meninges of the anterior and middle cranial fossae. From the meninges, the virus extends to the adjacent brain where it affects the temporal and inferior frontal lobes first and more severely, and then spreads to the rest of the brain. Adult HSV encephalitis is limited to the brain.
Herpes Simplex
Its symptoms are fever, confusion, coma, and seizures. In addition, because of the involvement of the frontal and temporal lobes, patients often display bizarre behaviour, personality changes, anosmia, and gustatory hallucinations. Survivors may have Korsakoff's amnesia, dementia, and seizures.
Creutzfeldt-Jakob disease
The human prion diseases are:

Creutzfeldt-Jakob disease (sporadic, familial, iatrogenic, and variant CJD)(see below).
Kuru.
A now-extinct disease of New Guinea natives, transmitted by eating the brains of dead persons who had the disease
The most common animal prion diseases are:
Bovine spongiform encephalopathy (BSE)-mad cow disease.
prion diseases
Pathology, in prion diseases, develops only in the brain. No other organ is affected. Early on, neurons develop intracytoplasmic vacuoles. As the disease progresses, vacuolization becomes more pronounced and the cortical neuropil develops a spongy appearance, hence the term
Creutzfeldt-Jakob disease (CJD)
Creutzfeldt-Jakob disease (CJD) is the most common prion disease of humans, but overall is a rare disease

It affects middle aged or old persons and causes dementia, myoclonus, ataxia and other neurological abnormalities.

The EEG shows perodic sharp wave complexes.

CJD is inexorably progressive and fatal within months up to 1 to 2 years.

A definitive diagnosis can only be made by microscopic examination of brain tissue showing the characteristic spongy change.
Brain abscess
Brain abscess causes loss of neurological function due to destruction of brain tissue. More important, it causes increased intracranial pressure. Its mass effect is due to the collection of pus and to cerebral edema around the abscess. Since the infection is contained within brain tissue, the CSF usually shows only a few mononuclear cells with normal protein and glucose.
HIV
HIV also infects the nervous system directly, causing aseptic meningitis, encephalitis, leukoencephalopathy, myelopathy, neuropathy, and myopathy. The most common of these direct effects, HIV encephalitis (AIDS-dementia complex), causes progressive memory loss, intellectual deterioration, behavioral changes, and motor deficits. Pathologically, HIV encephalitis is characterized by diffuse myelin damage (spongy myelinopathy, gliosis), neuronal loss, vascular damage, microglial nodules, and lymphocytic infiltrates. HIV envelope glycoproteins cause the membranes of HIV-infected macrophages to fuse, forming multinucleated giant cells (MGC) which are the hallmark of HIV encephalitis. The inflammatory reaction in HIV encephalitis is mild compared to other CNS infections, because patients are immunodeficient.