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ATAXIA Flashcards

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USMLE® Step 1 flashcards
1
Q

What does ataxia mean?

A

Without order

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2
Q

What are the symptoms of ataxia?

A 
Incoordination
Imbalance
Wide base
Speech disturbances (dysarthria)
Eye disturbances (nystagmus)
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3
Q

What are the clinical symptoms if the vestibulocerebellum is damaged?

A
  • eye disturbances

- wide stance that indicates difficulty balancing

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4
Q

What are the clinical symptoms if the spinocerebellum is damaged?

A
  • wide based irregular steps with lateral veering

- action tremor of limbs

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5
Q

What are the clinical symptoms if the cerebrocerebellum is damaged?

A
  • delayed initiation and termination of movement
  • slow to initiate a movement on command
  • tendency to overshoot a target (dysmetria)
  • inability to perform continuous repetitive movements (dysdiadochokinesia)
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6
Q

What causes cerebellar ataxia?

A

dysfunction of cerebellum and its connecting pathways

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7
Q

Describe labyrinthine ataxia

A
  • vestibular disorders
  • signals from the inner ear do not reach the brainstem and the cerebellum
  • no speech defects
  • limb movements are coordinated
  • impaired gait and balance
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8
Q

Describe sensory ataxia

A
  • malfunction of sensory input
  • failure of transmission of proprioception to the CNS
  • no eye disturbances
  • incoordiation increases dramatically when eyes closed
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9
Q

Describe acquired ataxia

A 
Where symptoms develop suddenly as a result of:
Cerebellar haemorrhage
Toxins and nutritional deficiencies
Tumours
Endocrine disease
Infectious causes
Inflammation
Cerebral palsy
Parneoplastic syndrome
Cerebellar ischemic stroke
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10
Q

Describe hereditary ataxia

A 
It develops slowly over many years.
3 types:
X linked ataxias
Autosomal dominant
Autosomal recessive
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11
Q

Describe x-linked ataxia

A

Type of hereditary ataxia.

Fragile x-associated tremor and ataxia syndrome

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12
Q

Describe autosomal dominant ataxia

A

Type of hereditary ataxia.
Two types:
- spinocerebellar ataxia
-episodic ataxia (2 types)

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13
Q

What are the different autosomal recessive ataxias?

A
  • Freidreich’s ataxia
  • Ataxia telangiesctasia
  • Ataxia with Vitamin E deficiency (treatable)
  • Ataxia with coenzyme Q10 deficiency (treatable)
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14
Q

How is ataxia diagnosed?

A
  • History of symptoms and family history required
  • neurological exams
  • laboratory tests
  • brain imaging scans
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15
Q

What neurological exams are used to diagnose ataxia?

A

Tandem walk - test for drunk drivers, gait needs to be narrowed to achieve this

Test for dysmetria - evaluation of point to point movement

Test for dysdiadochokinesis - evaluation of rapidly alternating movement

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16
Q

What laboratory tests are used to diagnose ataxia?

A

Measure blood pressure, blood tests for drugs,
vitamin levels, thyroid function, toxins and metals,
HIV and other infections, parneoplastic antibodies

Lumbar puncture

Brain imaging scans

Genetic tests

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17
Q

Describe CT scans

A 
Computerised tomography scan
series of X-rays are taken and assembled into 3-D
image of brain
takes 5 mins
half the price of an MRI scan
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18
Q

Describe MRI scans

A

Magnetic resonance imaging scan
strong magnetic fields and radio waves to produce
detailed scans of the soft tissue of brain

19
Q

What are symptomatic treatment options for ataxia?

A
  • Physical therapy
  • Speech therapy
  • Diet modifications - it becomes more difficult to swallow so diet is often modified for maximum consumption. Often a feeding tube is required
  • Action tremor may respond with drug treatment
  • Use of walking aids/wheelchair will give individual freedom of movement
20
Q

What type of hereditary ataxias are treatable?

A
  • Ataxia with vitamin E deficiency
  • Ataxia with coenzyme Q10 deficiency
  • Episodic ataxia type 2
21
Q

How is acquired ataxia treated?

A

Depends on underlying cause and how much damage

Complication of infection - antibiotics or anti-virals

Stroke or haemorrhage - correct high blood pressure,
thinning of blood to prevent further clots

Alcohol or toxins - avoid

Tumour - surgery

22
Q

What tissues are affected in Friedreich’s ataxia?

A
  • Primary sensory neurons in dorsal root ganglion
  • Cerebellum (superior cerebellar peduncle)
  • Heart (hypertrophic cardiomyopathy)
  • Pancreas (diabetes)
23
Q

Describe Friedreich’s ataxia

A
  • First described in 1860s by Nicholaus Friedreich
  • Recessively inherited form of ataxia
  • Onset of symptoms between 5 and 15 years
  • Progressively lethal
  • Gait disturbances/difficulty walking (ataxia)
  • Curving of spine to one side (scoliosis)
  • Slowness and slurring of speech (dysarthria)
  • Hearing and vision loss
24
Q

Describe the inheritance of Friedreich’s ataxia

A

Most common inherited ataxia
Affects about 1 in 50,000
Carrier frequency between 1:60 and 1:100

25
Q

What causes Friedreich’s ataxia?

A

Location of defect mapped to chromosome 9 in 1988

Frataxin gene was identified in 1996

The defect is a mutation - an unstable expansion of GAA repeat (repeated 66-1700 times) in the first intron resulting in a shortage of frataxin produced (13-30& of normal levels)

26
Q

Where is the frataxin protein found?

A

In the mitochondria

27
Q

What happens as a result of loss of frataxin?

A

Deficiency Fe-S containing proteins/ Mitochondria overloaded with iron

Inefficient electron transfer chain
increase reactive oxygen species

Impaired energy production

Damage to cells of nervous system, heart, pancreatic β-cells

28
Q

How can protein expression be increased as a therapeutic option for FA

A

Recombinant human erythropoietin:

  • improvement of ataxia and cardioprotective effects
  • reduced DNA damage and oxidative damage
  • increase in frataxin protein is post-transcriptional

Histone deacetylase (HDAC) inhibitors:
- alter heterochromatin structure (acetylation of histones associated with
higher levels of transcription)
- Compound 106 restored frataxin levels in mouse model
- Picked up by pharmaceutical company to carry out further animal and
safety trials

29
Q

What antioxidants can be used as therapeutic treatment for FA?

A

Idebenone

Mitoquinone

Coenzyme Q10-vitamine E hybrid (EPI –A0001)

EGb 761 (Ginkgo bilboa extract)

30
Q

What iron chelators can be used as therapeutic treatment for FA?

A

Deferiprone

PCTH (2-pyridylcarboxaldehyde 2-thiophencarboxyl hydrazone)

31
Q

What is the function of frataxin?

A

It is required for efficient regulation of cellular iron homeostasis.

It is involved in assembly of iron-sulfur clusters.

32
Q

Describe Autosomal dominant spinocerebellar ataxias (SCAs)

A
  • Group of inherited neurodegenerative disorders
  • Different genetic defects and variable phenotypes
  • All characterized by postural abnormalities, progressive motor incoordination, cerebellar degeneration
  • Autosomal dominant; family history
  • Some forms of SCA are fatal but not all
33
Q

What are the 5 types of SCA by clinical phenotype?

A

Type I - Ataxia + degeneration of other neuronal systems

Type II - Ataxia + degeneration of retina

Type III - Pure cerebellar ataxia

Type IV - Ataxia + myoclonus

34
Q

What are the loci associated with SCA?

A

There are more than 40 different loci associated with SCA

35
Q

What are the genes and mutations that cause SCA?

A
  • poly glutamine (CAG) expansions
  • Non coding CAG and non CAG repeat expansions
  • Conventional mutations
36
Q

What are the symptoms of SCA1?

A

They begin in early adulthood.

  • Ataxia
  • eye disturbances
  • speech/swallowing difficulties
  • cognitive impairment
37
Q

What is the pathology of SCA1?

A
  • severe loss of Purkinje cells (greatest in vermis)
  • some loss of granule cells
  • loss of olivary neurons in brain stem
  • loss of afferent fibers in middle and inferior cerebellar peduncles
  • loss of neurons in spinal cord
38
Q

What causes SCA1?

A

Polyglutamine expansion results in increased levels of phosphorylated protein in nucleus; alters gene expression; Purkinje cell’s protein repertoire altered; cerebellar output and survival of Purkinje cells altered glutamine expansion affects folding, interaction with other transcription factors and post translational modification of ataxin-1

39
Q

How does expanded CAG (polyglutamine) repeat cause SCA1?

A

Presence of expanded polyglutamine repeat in protein alters interaction of ataxin 1 with other transcription factors

Reduced expression of proteins involved in calcium
signaling/buffering, glutamate removal (EAAT4; excitatory amino acid
transporter 4)

Loss of calcium buffering proteins and ability to remove glutamate may cause disease

40
Q

What are the symptoms of SCA6?

A

Pure cerebellar symptoms (abnormal eye movements, slurred speech, progressive imbalance and limb incoordination)

41
Q

What causes SCA6?

A

Alternative splicing results in high level of mutant protein with expanded glutamine being expressed in Purkinje cells; explains cell selectivity but not mechanism; not known if changes in calcium levels occur.

42
Q

What causes SCA13?

A

Mutations affect potassium channel properties; unable to sense change in membrane potential or result in slow closure of channels; takes longer for Purkinje cell to regain resting membrane potential after action potential; slows Purkinje cell firing frequency; cerebellar output reduced

43
Q

What are the clinical symptoms of SCA13?

A 
Dysarthria, nystagmus
and gait ataxia
Cerebellar atrophy
without brainstem
involvement
Epilepsy and mental
retardation

Medical Sciences (9 decks)

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