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Demyelination and dementia Flashcards

1
Q

What does the insulation of axons by oligodendrocytes achieve?

A
  • locally confines neuronal depolarisation - protects axons - forms nodes of ranvier
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2
Q

What is the function of nodes of ranvier?

A

Precipitate rapid saltatory conduction

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3
Q

What is demyelination?

A

Preferential damage to myelin sheath

Relative preservation of axons

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4
Q

What are the causes of primary demyelination?

A
  • multiple sclerosis
  • acute haemorrhagic encephalomyelitis
  • acute haemorrhagic leukoencephalitis
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5
Q

What are the causes of secondary demyelination?

A

Viral

Progressive multifocal leukoencephalopathy

Metabolic

Central pontine myelinosis

Toxic

CO, organic solvents, cyanide

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6
Q

What is the commonest demyelinating disease?

A

Multiple Sclerosis

Prevalence of 1/1000

Female:Male ratio is up to 2:1

Peak incidence in 20-30 years

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7
Q

Define multiple sclerosis?

A

Auto-immune demyelinating disorder characterised by distinct episodes of neurological deficits, separated in time, and which correspond to spatially separated foci of neurological injury

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8
Q

What criteria is there for the clinical diagnosis of MS?

A
  • two distinct neurological defects occuring at different times
  • a neurological deficit implicating one neuro-anatomical site, and a MRI appreciated defect at another neuro-anatomical site
  • multiple distinct (usually white matter) CNS lesions on MRI
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9
Q

What is supportive of a diagnosis of MS?

A

Visual evoked potentials (evidence of slowed conduction)

IgG oligoclonal bands in CSF

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10
Q

Describe the presentation of MS

A

Optic nerve lesions (optic neuritis)

Unilateral visual impairment

Spinal cord lesions

Motor or sensory deficit in trunk and limbs

Spasticity

Bladder dysfunction

Brain stem lesions

Cranial nerve signs

Ataxia

Nystagmus

Internuclear opthalmoplegia

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11
Q

Describe the progression of MS

A

Acute or indisious onset

Relapsing and remiting

Later becomes progressive

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12
Q

Describe the morphology of multiple sclerosis?

A

Principally a white matter disease

The exterior of brain remains normal

Cut surface of the brain shows ‘plaques’

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13
Q

What are plaques?

A

Well circumscribed, well demarcated

Irregular shaped areas

Have a glassy, almost translucent appearance

Vary from very small to large lesions

Non-anatomical distribution

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14
Q

What locations are frequently affected by plaque?

A
  • adjacent to lateral ventricles
  • Corpus callosum
  • Optic nerve and chiasm
  • Brainstem
  • Ascending and descending fibre tracts
  • Cerebellum
  • Spinal Cord
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15
Q

Describe the pathogenesis of plaques

A

Active Plaques

  • perivascular inflammatory cells
  • microglia
  • ongoing demyelination

Inactive Plaques

  • gliosis
  • little remaining myelinated axons
  • oligodendrocytes and axons reduced in number
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16
Q

What are shadow plaques?

A

May reflect a degree of demyelination
Demonstrate thinned out myelin sheaths at the edge of lesions

Result in a less well defined lesion

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17
Q

What is the macroscopic appearance of acute (Active lesions)

A

Demyelinating plaques are yellow/brown, with an ill-defined edge which blends into surrounding white matter

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18
Q

What is the macroscopic appearance of chronic (inactive) lesions

A

Well-demarcated grey/brown lesions in white matter, classically situated around lateral ventricles

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19
Q

What environmental factors are associated with MS?

A

Latitude

Relationship with Vitamin D deficiency. sunlight exposure?

A viral trigger remains hypothesised

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20
Q

What genetic factors are found in MS?

A
  • 15 x risk if 1st degree relative has MS
  • 150x risk with an affected monozygotic twin
  • genetic linkage to HLA DRB1
  • GWAS found association with polymorphism in IL-2 and IL-7
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21
Q

Why is MS an immune mediated disease?

A
  • lymphocytic infiltration in histology
  • oligoclonal IgG bands in CSF
  • genetic linkage to HLA DRB1
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22
Q

What T- cell factors are thought to be associated with MS?

A

TH1 cells- IFN-g activating macrophages

TH17 cells- recruiting and activating damaging leukocytes

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23
Q

What are the humeral factors associated with MS?

A
  • Oligoclonal IgG bands on CSF
  • Anti B-cell (antibody producing lymphocytes) therapies reduce relapses and frequency of myelinating lesions
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24
Q

What are the degenerative diseases of the cerebral cortex?

A

Alzheimers disease, Pick disease, CJD

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25
What are the degenerative diseases of the basal ganglia and brainstem?
Parkinsons disease, progressive supranuclear palsy, multiple system atrophy, huntington disease
26
What is the spinocerebellar degenerative disease?
Spinocerebellar ataxia (e.g. friedreich ataxia)
27
What is the degenerative disease of motor neurones?
Motor neuron disease
28
What are degenerative diseases pathologically classified by?
Simple neuronal atrophy and subsequent gliosis
29
Define dementia
An acquired persistent generalised disturbance of higher mental functions in an otherwise fully alert person
30
What are the causes of primary dementia?
- Alzheimer's disease - Lewy body dementia - Pick's disease (fronto-temporal dementia) - Huntington's disease
31
What are the causes of secondary dementia?
- multi-infarct (vascular) dementia - infection (HIV, syphillis) - Trauma - Metabolic - paraneoplastic syndromes - intracranial SOL - chronic hydrocephalus - Drugs and toxins (alcohol) - Vitamin deficiencies (vitamin B1 )
32
Who is affected by alzheimer's disease?
F:M 2:1 40% prevalence in over 85s
33
How is dementia inherited?
Usually sporadic May be familial (1%) *Implicated genes: amyloid precursor protein (APP), presenilin 1 &2)* Increased incidence in trisomy 21
34
What does alzheimers disease cause?
Initially- impairment of higher intellectual function, with alterations in mood and behaviour Later- Progressive disortientation, memory loss and aphasia indicate severe cortical dysfunctino Can result in profound disability, muteness and immobility
35
Describe the macroscopic pathology of dementia
* Decreased size and weight of brain (cortical atrophy) * Location: frontal, temporal and parietal lobe atrophy * widening of sulci * Narrowing of gyri * Compensatory dilatation ventricles, secondary hydrocephalus ex vacuo * occipital lobe spared, brainstem and cerebellum normal
36
What are the microscopic features of alzheimers disease?
* extensive neuronal loss with associated astrocyte proliferation * neurofibrillary tangles * neuritic plaques * amyloid angiopathy
37
Where are neurofibrillary tangles found?
In hippocampus and temporal lobe Intracytoplasmic Tau protein, associated with microtobules
38
What are neuritic plaques also called?
Aß amyloid plaques Surrounding astrocytes and migroglia
39
How is Aß produced?
By cleavage of amyloid precursor protein (APP)
40
Where is APP found?
Chromosome 21
41
Where are presenilin 1 and presenilin 2 found? Where is apolipoprotein E found?
Presenilin 1= chromosome 14 Presenilin 2= chromosome 1 Allele e4
42
What is amyloid angiopathy?
Extracellular eosinophillic accumulation
43
What is the structure of amyloid angiopathy
Polymerised beta pleated sheets formed by Aß
44
Amyloid angiopathy stains with what?
Congo red
45
What does amyloid angiopathy cause?
Disruption of BBB - serum leaking - oedema - local hypoxia
46
Lewy body dementia makes up \_\_-\_\_% of dementias
Lewy body dementia makes up 10-15% of dementias
47
Lewy body demendia presents how?
Progressive dementia, along with hallucinations and fluctuating levels of attention/cognition Fluctuation in severity on a day to day basis Features of parkinsonism present at onset, or emerge shortly after
48
What is the clinical presentation of parkinsonism?
Loss of facial expression Stooping Shuffling gait Slow initiation of movements Stiffness Pill rolling tremor
49
What conditions affect the nigro-striatal dopaminergic pathway and cause parkinsonism?
Idiopathic parkinsons diseae Lewy body dementia Drugs (phenothiazines) Trauma (dementia puglistica) Multi-system atrophy Progressive supranuclear palsy Cortico-basal degeneration
50
What are the pathological features of lewy body dementia?
Degeneration of the substantia nigra
51
What is seen macrospically in lewy body dementia?
Pallor in the substantia nigra, where pigmented dopaminergic neurones run
52
What is seen microscopically in lewy body dementia?
Loss of pigmented neurons Reactive gliosis, microglial accumulation Remaining neurons may show lewy bodies Fewer cortical lewy bodies
53
What are lewy bodies?
- single/multuple intracytoplasmic, eosinophilic, round to elongated bodies that have a dense core and a surrounding pale halo - Aggregates of a-synuclein and ubiquitin
54
Huntingtons disease is a relentlessly ______ neuropsychiatric disorder, onset most comminly between the ages of \_\_-\_\_ but can occur at any time
Huntingtons disease is a relentlessly progressive neuropsychiatric disorder, onset most comminly between the ages of 35-50 but can occur at any time
55
What are the clinical features of huntingtons disease?
Triad of emotional, cognitive and motor disturbance Develop dementia later
56
What ar the symptoms of huntingtons disease?
* chorea * myoclonus * clumsiness * slurred speech * depression * irritability * apathy
57
Where is the hintintin gene?
On chromosone 4p
58
When is the huntingtin gene normal?
If \< 28 repeats, disease penetrant if more than 34
59
What is the macroscopic pathology of huntingtons?
Atrophy of basal ganglia: caudate nucleus; putamen Cortical atrophy occurs later
60
What is the microscopic pathology of huntingtons disease?
Simple neuronal atrophy of striatal neurones in the basal ganglia Pronounced astrocytic gliosis
61
Pick's disease is a ________ dementia commencing in ___ \_\_\_\_ (usually between __ and __ years) characterised by progressive changes in _______ and _____ deterioration leading on to impairment of \_\_\_\_\_\_\_, ______ and \_\_\_\_\_\_\_\_
Pick's disease is a progressive dementia commencing in middle life (usually between 50 and 60 years) characterised by progressive changes in character and social deterioration leading on to impairment of intellect, memory and language
62
What are the symptoms of pick's disease?
Personality and behavioural changes speech and communication problems changes in eating habits reduced attention span
63
Picks disease may last between _ to __ years, the mean length of illness is around _ years.
Picks disease may last between 2 to 10 years, the mean length of illness is around 7 years.
64
What is the macroscopic pathology of pick's disease?
Extreme atrophy of cerebral cortex and later in temporal lobes Brain weight \<1kg Neuronal loss and gliosis
65
What are the histological hallmarks of FTD?
Pick's cells (swollen neurons) Intracytoplasmic filamentous inclusions known as pick's bodies
66
Define multi-infarct 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
67
Multi-infarct dementia is more common in ______ then in \_\_\_\_\_. It commonly occurs after the age of \_\_, but also seen in middle aged \_\_\_\_\_\_\_\_\_\_\_ Sufferers are aware of their mental deficits and are prone to ________ and \_\_\_\_\_\_
Multi-infarct dementia is more common in men then in women. It commonly occurs after the age of 60, but also seen in middle aged hypertensives Sufferers are aware of their mental deficits and are prone to depression and anxiety
68
What clues help to differentiate MID from alzheimer's disease?
- abrupt onset - stepwise progression - history of hypertension or stroke - evidence of stroke will be seen on CT or MRI
69
What is the commonest morphological appearance of MID?
* Large vessel infarcts * Scattered throughout hemispheres * Atheroma of large cerebral arteries provoke thromboembolism
70
What is a rarer morphological appearance of MID?
Small vessel (lacunar) infarcts Central, subcortical distribition
71
What are small vessel (lacunar) infarcts associated with?
Longstanding hypertension and arteriosclerosis of small vessels

Neurology (41 decks)

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