Neuropathology 2 Flashcards
What do oligodendrocytes do?
Insultate axons
Locally confine neuronal depolarisation
Protect axons
Form nodes of Ranvier
What do nodes of ranvier precipitate?
Rapid saltatory conduction
What does damage to oligodendrocytes do?
Damaged neuronal conduction
What is demyelination?
Preferential damage to the myelin sheath, with relative preservation of axons
Demyelinating disorders can be either?
Primary or secondary
Name 3 primary demyelinating disorders.
- Multiple Sclerosis.
- Acute disseminated encephalomyelitis. (post-infectious AI disorder, mild, self-limiting, kids)
- Acute haemorrhagic leukoencephalitis. (post-infectious AI disorder, rapidly fatal, adults)
Outline 3 secondary demyelinating disorders.
- Viral – progressive multifocal leukoencephalopathy (PML).
- Metabolic – central pontine myelinosis.
- Toxic – CO, organic solvents, cyanide.
What is the most common demyelinating disease?
MS
What is the female to male ratio in MS?
2:1
What is the peak age incidence in MS?
20-30 years old
What does MS have a well known association with?
Latitude
What is MS defined as?
An auto-immune demyelinating disorder, characterised by distinct episodes of neurological deficits, separated in time, and which correspond to spatially separated foci of neurological injury
For a clinical diagnosis of MS, what is needed?
- 2 distinct neurological defects occurring at different times
- A neurological defecting implicating one neuro-anatomical site, and a MRI-appreciated defect at another neuro-anatomical site
- Multiple distinct (usually white matter) CNS lesions on MRI
What also supports a diagnosis of MS?
- Visual evoked potentials (evidence of slowed conduction)
* IgG oligoclonal bands in CSF
What would be seen in the CSF of a patient with MS?
IgG oligoclonal bands
Where is presentation of MS usually?
Within a focal neurological deficit
Give an example of a focal neurological deficit.
Optic nerve lesions - optic neuritis
- unilateral visual impairment
Onset of MS is?
Acute OR Insidious
Describe the complications of a spinal cord lesion.
- motor or sensory deficit in trunk and limbs.
- spasticity.
- bladder dysfunction
Describe the complications of a brain stem lesion.
- cranial nerve signs.
- ataxia.
- nystagmus.
- internuclear ophthalmoplegia.
Describe the course of MS.
Can be relapsing and remitting, later becoming progressive
In areas corresponding to white matter, what does demyelination show up as on an MRI?
Hyperintense regions on T2 weighted MRI scans
What is MS a disease of?
WHITE matter
Therefore, how does the external surface of the brain appear?
NORMAL
What does the cut surfaces of the brain in MS show?
Plaques
Describe the appearance of plaques in MS.
Well circumscribed, well-demarcated.
Irregularly shaped areas.
Glassy, almost translucent appearance.
Vary from small to large lesions.
What is the distribution of plaques in MS like?
Non-anatomical
List areas which are frequently affected by plaques.
- Adjacent to lateral ventricles
- Corpus callosum
- Optic nerves and chasm
- Brainstem
- Descending and ascending fibre tracts
- Cerebellum
- Spinal cord
Describe the histology of active plaques.
- Perivascular inflammatory cells
* Ongoing demyelination
Describe the histology of inactive plaques.
- Gliosis
- Little remaining myelinated axons
- Oligodendrocytes and axons reduced in numbers
What may ‘shadow’ plaques represent?
A degree of RE-myelination
What do shadow plaques demonstrate at the edge of lesions?
Thinned out myelin sheaths
What do shadow plaques result in?
Less well defined lesions
Macroscopically, how do active plaques appear?
Demyelinating plaques are yellow/brown, with an ill-defined edge which blends into surrounding white matter
Describe the macroscopic appearance of inactive plaques.
- Well-demarcated grey/brown lesions in white matter
* Classically situated around lateral ventricles
What environmental factors may MS be associated with?
- Latitude
- Vit D deficiency - lack of sun
- Viral trigger remains hypothesised (ie. EBV)
What does MS have a genetic linkage to?
HLA DRB1
IL-2 and IL-7
Outline how MS is an immune-mediated disease.
- Lymphocytic infiltration in histology
- Oligoclonal IgG bands in CSF
- Genetic linkage to HLA DRB1
- T cell factors
What therapy reduces relapses and frequency of demyelinating disorders?
Anti- B cel
Give examples of degenerate disorders affecting the cerebral cortex.
Alzheimer’s Disease
Pick Disease
CJD
Give examples degenerate disorders affecting the basal ganglia and brainstem.
Parkinson Disease
Progressive Supranuclear Palsy
Multiple System Atrophy
Huntington Disease
Give examples of degenerate disorders affecting spinocerbellar areas
Spinocerebellar ataxias (ie. Friedereich Ataxia).
Give examples of degenerate disorders affecting motor neurones
MND
What are degenerate disorders characterised by?
Simple neuronal atrophy, and subsequent gliosis
What is dementia?
An acquired and persistent generalised disturbance of higher mental functions in an otherwise fully alert person
What are neurodegenerative disorders characterised by?
- Progressive loss of neurons.
* Typically affecting functionally related neuronal groups.
Name the 4 primary dementias.
- Alzheimer’s disease
- Lewy body dementia
- Pick’s disease (fronto-temporal dementia)
- Huntington’s disease
What are secondary dementias?
Disorders that give rise to dementia
What is the most common subtype of dementia?
Alzheimers
What is the 2nd most common subtype of dementia?
Vascular dementia
List causes of multi-infarct (vascular) dementia.
Infection (HIV, syphilis) Trauma Metabolic Drugs and toxins (alcohol) Vitamin deficiencies (Vitamin B1) Paraneoplastic syndromes Intracranial space occupying lesions Chronic hydrocephalus
What is the female to male ratio of Alzheimers?
2:1
Why does Alzheimers most commonly arise?
Usually sporadic
What genes may be found in Alzheimers?
- Amyloid precursor protein (APP)
* Presenilin 1 + 2.
What is there an increased incidence of Alzheimers in?
Trisomy 21 - amyloid precursor protein
Describe clinically, what Alzheimers is like at the beginning?
Insidious impairment of higher intellectual function with alterations in mood and behaviour
What happens later in Alzheimers? What does this indicate?
Progressive disorientation, memory loss, aphasia
SEVERE CORTICAL DYSFUNCTION
How does death in Alzheimers usually occur?
Due to secondary cause e.g pneumonia
What happens to the size of the brain in Alzheimers?
DECREASES - due to cortical atrophy
What areas of the brain are most commonly affected by atrophy in Alzheimers?
Frontal, temporal and parietal lobe atrophy
What happens to sulci in Alzheimers?
They become wider
What happens to gyri in Alzheimers?
They become more narrow
How is the ventricular system in Alzheimers affected?
There is compensatory dilatation of the ventricles, and secondary hydrocephalus ex vacuo
What areas are normal/spared in Alzheimers?
The occipital lobe, brainstem and cerebellum
What are the 4 main microscopic features of Alzheimers?
- Extensive neuronal loss, with associated astrocyte proliferation - simple neuronal atrophy and gliosis
- Neurofibrillary tangles
- Neuritic plaques
- Amyloid angiopathy
Where in the brain are Neurofibrillary Tangles found?
In the hippocampus and temporal lobe
Are neurofibrillary tangles extra or intracytoplasmic?
Intracytoplasmic
What, associated with microtubules, is seen in Alzheimers and other degenerate diseases?
Tau protein
What are Aß amyloid plaques also called?
Neuritic plaques
What do Aß amyloid plaques surround?
Astrocytes and microglia
What is Aß amyloid the central element of?
Neuritic plaques
What is Aß produced by?
Cleavage of amyloid precursor protein (APP)
What is trisomy 21 associated with the early onset of?
Alzheimers
What is trisomy 21 associated with?
Amyloid precursor protein (APP) is on chromosome 21
What mutations are implicated in familial Alzheimers?
- Point mutations in APP
- Presenilin 1
- Presenilin 2
What chromosome is the gene for Presenilin i) 1 ii) 2 located on?
i) 14
ii) 1
What is the commonest familial cause of Alzheimer’s? What does this do?
Apolipoprotein E e4 allele – dysregulates APP
What are thought to be the main toxic lesions in Alzheimers?
Abeta Oligomers
What are neuritic plaques composed of?
Amyloid, formed from oligomerisation of Ab oligomers
What do Ab oligomers promote?
Hyper-phosphorylation and mis-localisation of TAU
What does the mislocation of TAU appear to do?
Enhance the excitotoxicity affect of Abeta oligomers
What do fibrillary tangles arise due to?
Abnormal organisation of the cytoskeleton; hyperphosphorylated TAU protein is insoluble in vivo
What lesion does Alzheimers demonstrate?
Cerebral amyloid angiopathy
What is the amyloid that accumulates in cerebral amyloid angiopathy in Alzheimers?
Ab, which accumulates in the wall of arterioles
What colour does amyloid stain?
Congo red
What is the effect of the accumulation of Ab?
Stiffens and thickens vessel walls, disrupting the BBB
What does Stiffens and thickens vessel walls, disrupting the BBB lead to?
- Serum leaking
- Oedema
- Local hypoxia
What accumulated extracellular in amyloid angiopathy?
Eosinophils
What does Ab form?
Polymerised beta sheets
What does Ab form?
Polymerised beta pleated sheets
Name important features of Lewy Body dementia.
- Progressive dementia.
- Hallucinations.
- Fluctuating levels of attention/cognition.
- Fluctuation in severity on a day-to-day basis.
- Features of Parkinsonism are present at onset, or emerge shortly after.
Lewy body dementia can show an overlap with Parkinson’s. What are the differences?
- Characterised by fluctuating cognitive dysfunction, including attention.
- MEMORY is affected LATER in the course of the disease
What are the clinical features of Parkinson’s?
- Loss of facial expression. (hypomimia)
- Stooping.
- Shuffling gait.
- Slow initiation of movements.
- Stiffness and pin rolling tremor.
What is hypomimia?
Loss of facial expressions
Most cases of Parkinson’s are ______
IDIOPATHIC
What is the pathology of lewy body dementia?
Degeneration of the substantia nigra
In what condition can you also see degeneration of the substantia nigra?
Parksinson’s
Macroscopically, what is seen in lewy body dementia?
Pallor in the substantia nigra, where pigmented dopaminergic neurones run
You get MORE cortical lewy bodies in Dementia
FALSE - LESS
What are the microscopic features of lewy body Dementia?
- Loss of pigmented neurones.
- Reactive gliosis and microglial accumulation.
- Remaining neurones may show Lewy bodies:
- “Single / multiple intracytoplasmic, eosinophillic, round to elongated bodies that have a dense core and a surrounding pale halo”
- Aggregates of a-synuclein and ubiquitin
What is Huntington’s disease?
A relentlessly progressive neuropsychiatric disorder
When does onset of Huntington’s occur?
Most commonly between the ages of 35-50, but can occur at any time.
What is the triad of clinical features in Huntington’s?
A triad of emotional, cognitive and motor disturbance
What are the symptoms of Chorea?
- Chorea (dance-like movements).
- Myoclonus.
- Clumsiness.
- Slurred speech.
- Depression.
- Irritability.
- Apathy.
When do people with Huntington’s develop dementia?
Later on in the course of the disease
What is the inheritance pattern on Huntington’s?
Autosomal dominant
What chromosome is the Huntington’s gene on?
4p
Genetically, when does Huntington’s occur?
CAG repeats …. CAG CAG CAG CAG
<28 = normal
>35 = Huntington’s
Describe the macroscopical pathology of Huntington’s.
- Atrophy of basal ganglia: caudate nucleus, putamen.
* Cortical atrophy occurs later
Describe the microscopic pathology of Huntington’s.
- Simple neuronal atrophy of striatal neurones of the basal ganglia.
- Pronounced astrocytic gliosis.
What is Pick’s disease also known as?
Fronto-temporal dementia
What is Pick’s disease?
A progressive dementia, commencing in middle life (usually between 50 and 60 years) characterised by progressive changes in character and social deterioration leading to impairment of intellect, memory and language
What are the symptoms of Pick’s disease?
Sx related to frontal and temporal lobes:
- Personality and behaviour change.
- Speech and communication problems.
- Change in eating habits.
- Reduced attention span
Picks disease is a ______ ________ illness
RAPIDLY, PROGRESSIVE
How long does Pick’s disease last?
Between 2 to 10 years.
- the mean length of illness is ~ 7 years
What happens to the frontal and temporal lobes in Pick’s disease?
EXTREME atrophy - frontal lobe first then temporal
What does the weight of the brain end up being in Pick’s disease?
<1kg
What are the histological hallmarks of Pick’s?
- Pick’s cells – swollen neurones.
* Intracytoplasmic filamentous inclusions, known as Pick’s bodies.
What is vascular dementia?
Disorder involving a deterioration in mental functioning due to cumulative damage to the brain through hypoxia or anoxia (lack of oxygen) as a result of multiple blood clots within the blood vessels supplying the brain.
What is vascular dementia also called?
Multi-infarct dementia
What do successive, multiple, cerebral infarctions cause?
Increasingly larger areas of cell death and damage
What happens when a significant area of the brain is damaged?
Dementia results
Who is vascular dementia more common in?
MEN
Who gets vascular dementia?
Commonly after the age of 60
AND MIDDLE AGED HYPERTENSIVES
Sufferers of vascular dementia are aware of their mental defects, what can therefore happen?
Depression and anxiety
What is vascular dementia difficult to distinguish from?
Alzheimer’s
What clues help to diagnose vascular dementia from Alzheimer’s?
- Abrupt onset.
- Stepwise progression.
- Hx of hypertension or stroke.
- Evidence of stroke will be seen on CT or MRI.
Steadily progressing deterioration is?
Alzheimer’s
Step-wise deterioration, due to episodic vascular induced brain infarction is?
Vascular dementia
What provokes thromboembolism in vascular dementia?
Atheroma of large cerebral arteries
What would be seen in MID?
Large vessel infarcts