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CSGD Quiz 2 2005

1

Which ONE of the following statements is CORRECT about glioblastoma multiforme?


  The majority of glioblastomas multiforme respond to radiation therapy.

  Glioblastoma multiforme only occurs in men.

  Glioblastoma multiforme is the most malignant of the astrocytic brain tumours.

  Glioblastoma multiforme frequently metastatises to systemic organs.

  Glioblastoma multiforme arises from dura mater.


A is incorrect: GBM is aggressive and mortality is high. B is incorrect: GBM affects older patients and both sexes equally. C is correct: As for A. D is incorrect: Metastasis outside the CNS is often a late and/or rare complication of most CNS tumours. E is incorrect: GBM is a form of astrocytoma (glial cells).

2

A 14 year old boy presents with the clinical findings of progressive ataxia, absent reflexes and diminished joint position and vibration sesnation. Friedreich ataxia was diagnosed by DNA testing. Which ONE of the following was the most likely DNA test result?


  An expanded CAG repeat in the coding region of ataxin-2 gene.

  An expanded CAG repeat in intron 1 of ataxin-3 gene.

  A contracted GAA repeat in the coding region of frataxin gene.

  An expanded GAA repeat in intron 1 of frataxin gene.

  A point mutation in intron 1 of frataxin gene.


Ataxin-2 and 3 are genes responsible for SCA 2 and 3 respectively. FA is due to a GAA repeat in the first intron of the gene frataxin, not a polyglutamine (expanded CAG) as in the other conditions. Point mutations only account for 2% of FRDA.

3

Betty has recently suffered a stroke resulting from a thromboembolism in the territory of the left middle cerebral artery. Which ONE of the following statements about her condition is likely to be CORRECT?


  To confirm her diagnosis an MRI scan was required as a CT cannot distinguish an infarct from a haemorrhage.

  Her plantar response is flexor on the right side and extensor on the left side.

  Her capacity for repetition of a sequence of words is impaired.

  Weakness and sensory loss affect the arm and leg equally.

  She has no spontaneous speech and is unable to utter even single words.


A is incorrect: CTs will display haemorrhages brightly. B is incorrect: Would show a Babinski sign (extensor response) on the contralateral (right) side. C is correct: The lesion may affect Broca's area which would impair repetition. D is incorrect: The middle cerebral artery territory of supply usually does not include the lower limb motor areas (which are supplied by the anterior cerebral artery). E is incorrect: Broca's aphasia is non-fluent but complete inability to produce speech is not assured.

4

Which ONE of the following statements about subarachnoid haemorrhage is CORRECT?


  Rupture of a saccular aneurysm is the commonest non-traumatic cause of adult subarachnoid haemorrhage.

  Most saccular aneurysms which rupture are in the posterior fossa.

  Early clipping following aneurysm rupture is contraindicated.

  10% of babies are born with small saccular aneurysms.

  Rupture of a saccular aneurysm cannot result in cerebral infarction.


A is correct: Trauma is the most common cause of SAHs, but excluding trauma, aneurysm rupture is the most likely cause. B is incorrect: Saccular aneurysms occur at sites of weakness (e.g. arterial bifurcations) and are more common anteriorly than posteriorly. C is incorrect: Clipping may prevent repeated bleeds. D is incorrect: Babies "simply do not get" saccular aneurysms. E is incorrect: Rupture of an aneurysm can result in hypoperfusion of tissue that was previously being supplied distally to the vessel that has burst. After some time, blood products from the haemorrhage may also result in localised occlusion and infarction.

5

The whoop-whoop bird emits a 200Hz tone. A person who has difficulty in localising a whoop-whoop bird could have:


  Damage to hair cells near the apex of the right cochlear.

  Damage to hair cells near the base of the left cochlear.

  Damage to hair cells near the base of the left cochlear and to hair cells near the base of the right cochlear.

  A lesion in the central nervous system affecting cells sensitive to interaural intensity differences.

  A bilateral lesion in the frontal cortex.


200Hz is a relatively low frequency sound (< 1.5kHz). High frequency is considered to be > 5kHz, and anything between 1.5-5kHz is intermediate (and usually poorly localised). A is correct: Hair cells in the apex are responsive to low frequency noises, and therefore unilateral loss of these cells would result in difficulty localising low frequency sounds (localised based on timing). B is incorrect: Hair cells at the base are sensitive to high frequency sound. C is incorrect: As for B. D is incorrect: Intensity difference is used for localisation of high frequency sounds. E is incorrect: The frontal cortex is not involved in auditory processing.

6

Which ONE of the following statements about the cerebral hemispheres is CORRECT?


  If the motor cortex is damaged in infancy there is complete recovery of all motor function.

  During brain development, language is lateralised to a particular hemisphere earlier in females than in males.

  In about 70% of left-handed individuals speech/language is represented in the right cerebral hemisphere.

  A patient who has difficulties with motor planning and cognition is most likely to have damage in the posterior association cortex.

  Exposure to testosterone during development produces sexual dimorphism in specific hypothalamic nuclei in the brain.


A is incorrect: While the increased plasticity of young patients generally results in a better outcome, complete recovery is never assured. B is incorrect. C is incorrect: 70% of left-handed individuals still have language lateralised to the LEFT side of the brain. D is incorrect: The posterior association cortex is most involved in language and higher sensory functions. E is correct: The hypothalamus shows extensive sexual dimorphism which is responsive to sex hormone exposure during development.

7

Bill is a 34 year old who is interested in joining the air force. He has his eyes examined and is told that he has deuteranopia. Bill asks the doctor to explain what he means by deuteranopia. Which ONE of the following statements about deuteranopia is corrrect?


  Bill's retina contains all three types of cones, but the green cone functions abnormally.

  Bill's retina contains only two types of cones: red and green cones.

  Bill has an abnormal ability to perceive green hues because his retina has no green cones.

  Bill's retina contains all three types of cones, but the function of the red cone is abnormal.

  Bill's retina contains only one type of cone, the green cone.

8

Joan is a 45 year old woman who has been experiencing headaches. Her visual acuity is normal as is her colour vision. Her visual fields are shown below. The most likely cause of her problem is:




  Vascular disease in the right thalamus.

  A disease of the retina.

  A tumour that has affected the optic chiasm.

  Vascular disease affecting the optic radiations on the left side.

  A tumour within the left parietal lobe.


A is incorrect: A lesion to the right thalamus (i.e. lateral geniculate nucleus) would result in bilateral left field deficit. B is incorrect: A retinal disease could cause this, but the pattern of the deficit, combined with normal visual acuity, makes C more likely. C is correct: The deficit indicates that the nasal superior fibres of both eyes are involved, with the inclusion of the nasal inferior fibres of the right eye. A (slightly asymmetric) tumour could cause this. D is incorrect: If the left optic radiations were affected, one would expect a bilateral right field deficit. E is incorrect: A tumour of the left parietal lobe would cause right inferior quadrantanopia.

9

The following scenario applies to Q9 and Q10.

Parkinson's disease is characterised by akinesia, shuffling gate, rigidity, rest tremor and loss of postural reflexes. The origin of these symptoms is the progressive loss of dopaminergic neurons in the midbrain. L-dopa, a drug that is converted to dopamine upon entry into the CNS, can significantly ameliorate these symptoms.

The most likely bases of L-dopa's efficacy is:


  Dopamine is a centrally acting muscle relaxant which attenuates the tremors and thereby permits the normal execution of voluntary and complex (postural) reflex movement.

  The vast majority of neurons in the striatum (caudate and putamen) that degenerate in Parkinson's disease are dopaminergic and the provision of exogenous dopamine counteracts this loss.

  Dopamine excites glutamatergic neurons (which are excitatory and inhibits GABAeric neurons (which are inhibitory), the net result is an increase in the activity of the motor thalamus.

  Dopamine excites the remaining dopaminergic neurons in the substantia nigra which then increases dopamine release in the striatum which in turn increases activity of the motor thalamus.

  Dopamine excites neurons in the striatum that project in the direct pathway to the motor thalamus, and inhibits striatal neurons that project in the indirect pathway to the motor thalamus.


A is incorrect: Dopamine is not a muscle relaxant (its central action is to promote movement) B is incorrect: the degenerating dopaminergic neurons are in the SNpc, not the striatum C is incorrect: dopamine's action in the striatum is on GABAergic neurons (not glutamatergic) where it excites some and inhibits others D is incorrect: dopamine's action is on the striatum, not on the SN E is correct: Dopamine excites neurons in the striatum that project in the direct pathway to the motor thalamus, and inhibits striatal neurons that project in the indirect pathway to the motor thalamus.

10

Which ONE of the following statements is true of the symptoms of Parkinson's disease:


  The symptoms are likely to be the result of a combination of the basal ganglia's connections with the cerebral cortex and the basal ganglia's projections to the spinal cord.

  The basal ganglia make extensive connections to limbic, oculomotor and prefrontal cortex, but the most obvious deficits are in the basal ganglia-motor circuits.

  The inability to initiate movement is primarily a motivational problem, because normal movements can be elicited by external stimuli such as stripes on the floor.

  The loss of postural reflexes indicates that there is, at some level, a degree of dysfunction in the vestibular system (vestibulospinal tracts and their cerebellar modulation).

  The rest tremor could (in the absence of other symptoms) be mistaken for the rest tremor associated with cerebellar lesions.


A is incorrect: The basal ganglia do not project to the spinal cord. B is correct. C is incorrect: The inability to initiate movement is physiological due to the loss of dopaminergic neurons in the substantia nigra. D is incorrect: The vestibular system is not a affected in Parkinson's disease. E is incorrect: Cerebellar lesions are association with intention tremor