Cerebellar Disorders

Question 1

What is the function of the cerebellum?

Answer 1

• To make movements of the extremities, trunk and eyes as smooth as possible by continually making small corrections
  
  • coordinated contraction/relaxation of agonist & antagonist muscles

Question 2

What are the inputs of the cerebellum?

Answer 2

• **Inputs: **sensory (proprioception) pathways from spinal cord, cortex, brainstem

1. Motor information from cord ⇒ ventral spinocerebellar tract ⇒ superior cerebellar peduncle ⇒ cerebellum
2. Visual, sensory, motor information from cortex ⇒ pontine nuclei ⇒ middle cerebellar peduncle ⇒ cerebellum
3. Proprioceptive information from limbs ⇒ fasciculus gracilis/ cuneatus ⇒ dorsal spinocerebellar tract & cuneocerebellar tract ⇒ inferior cerebellar peduncle ⇒ cerebellum

Question 3

What are the outputs from the cerebellum?

Answer 3

• Outputs: brainstem (that then project back to extremities/trunk & eyes), thalamus

1. Cerebellum ⇒ VL thalamus ⇒ primary motor & supplementary motor cortex ⇒ ventral & lateral corticospinal tract ⇒ movement
2. Cerebellum ⇒ vestibular nuclei ⇒ head/eye control & posture
3. Cerebellum ⇒ medullary & pontine reticular formation ⇒ medullary & pontine reticulospinal tract ⇒ unconscious motor control

Question 4

Cerebellar deficits are ___________ to the lesion

Answer 4

ipsilateral

• due to:
  
  • ‘doublecrossing’ or
  • fibers remain ipsilateral

Question 5

Acute lesions accompanied by nausea/vomiting due to _______.

Answer 5

vertigo

• vestibular dysfunction similar
  
  • pts are not necessarily ataxic on finger to nose or heel to shin

Question 6

Ataxia

Answer 6

uncoordinated muscle movement

• errors in speed, range, force, timing

Question 7

**Truncal ataxia **

Answer 7

wide-based, unsteady gait or difficulty sitting up

• localizes to lesion of vermis
  
  • “drunk-like”
• Walk patient—normal walk & tandem walk
• Romberg test
  
  1. ask patient to stand in place, feet together & close eyes
  2. if s/he needs to step to stabilize, then deficit could be due cerebellar, proprioceptive, or vestibular dysfunction
  3. not specific to cerebellar disorders

Question 8

Appendicular ataxia:

Answer 8

difficulty coordinating an extremity

• manifests as dysmetria & dysrhythmia
• lesion of ipsilateral lateral hemispheres

Question 9

Appendicular ataxia:

1. Dysmetria:
2. Dysrhythmia:
3. Finger-nose-finger test:
4. Heel-to-shin test:
5. Finger tapping:
6. Dysdiadochokinesia:

Answer 9

1. **Dysmetria **= overshoot/undershoot of a body part (limb) during movement toward a target
2. Dysrhythmia = abnormal rhythm and timing of movement
3. Finger-nose-finger test—alternating between touching nose and examiner’s finger
   
   • abnormal if patient’s finger shakes as it approaches target (either nose or finger)
4. Heel-to-shin test—guiding heel along shin when supine
   
   • abnormal if heel shakes
5. Finger tapping—watch amplitude, rhythm, speed
   
   • cerebellar disorders cause abnormal rhythm, slowed speed, and varying amplitude
6. Dysdiadochokinesia = abnormal speed/rhythm when tapping hand with palm/dorsum alternatively

Question 10

Tremor:

• Postural Tremor:
• Action/Intention tremor:
• Titubation:

Answer 10

involuntary, rhythmic oscillation of a body part

• Postural tremor = tremor that occurs when a limb is held in a particular position (eg. open hands held extended)
  
  • lesion of ipsilateral lateral hemisphere
• Action/intention tremor = tremor that occurs when limb is in motion
  
  • lesion of ipsilateral lateral hemisphere
• Titubation = tremor of trunk or head
  
  • lesion of vermis

Question 11

Ocular dysmetria:

Answer 11

**overshoot or undershoot of the eyes as patient focuses on a target **

• lesion of flocculonodular lobe

Question 12

Eye movements:

• Saccades:
• Slow eye movements:

Answer 12

Eye movements:

• **Saccades: **quick, voluntary movement of eyes onto target
  
  • mediated by cortex—frontal & parietal eye fields
• **Slow eye movements: **involuntary movement of eyes
  
  • mediated by cerebellum, vestibular nuclei & pathways, and extraocular motor nuclei

Question 13

Nystagmus:

Answer 13

rhythmic oscillations of the eyes

• mediated by cortex
• an attempt by the cortex to correct abnormal signal to brain
• deficit of slow eye movements
• fast-beating phase of eye movements:
  
  • “right beating nystagmus”—fast phase of eye movements are to the right & slow phase of eye movements to left

Question 14

1. What causes a pure vertical nystagmus?
2. What causes a direction-changing nystagmus?
3. What causes a horizontal or rotary nystagmus?

Answer 14

1. Pure vertical nystagmus:
   
   • ALWAYS CNS lesion
2. Direction-changing nystagmus:
   
   • CNS lesion
3. Horizontal or rotatory nystagmus:
   
   • CNS or PNS lesion

Question 15

Lesion of vermis/flocculonodular lobe can cause _______, _________, or ______ nystagmus

Answer 15

vertical, horizontal, or rotatory

Question 16

1. R beating horizontal nystagmus on R gaze, upgaze, downgaze ⇒
2. R beating horizontal nystagmus on R gaze, L beating horizontal nystagmus on left gaze, vertical nystagmus on upgaze ⇒

Answer 16

1. L VOR or L vestibular nuclear lesion
   
   • lesion could be CNS or PNS w/ horizontal nystagmus
2. lesion is likely to be cerebellum or one of its pathways

Question 17

• Slow saccades:
• Scanning (ataxic) speech:
• Hypotonia of ipsilateral limb:
• Impaired VOR Suppression:

Answer 17

• **Slow saccades: **slowness in eye movements when trying to quickly look at target
• Scanning (or ataxic) speech: slow, effortful speech with difficulty articulating
  
  • lesion of lateral hemispheres
• **Hypotonia of ipsilateral limb: **b/c cerebellum influences corticospinal tracts
  
  • pt falls to weak side (ipsilateral to lesion)
• Impaired VOR suppression:
  
  • ​L VOR activated (i.e. head moving left) ⇒ moves eyes to the right
  • if you want to move head to L and eyes to L ⇒ need to suppress VOR
    
    • done by the L cerebellum (L flocculonodular)
  • L cerebellar lesion ⇒ no L VOR suppression ⇒ **cannot track movements moving R to L **

Question 18

Lateral Hemispheres:

• Function:
• Motor pathway influenced:
• Deficit if Lesioned:

Answer 18

• **Function: **Motor planning for extremities
• Motor pathway influenced: LCST
• **Deficit if lesioned: **Appendicular ataxia

Question 19

Intermediate hemispheres:

• Function:
• Motor pathway influenced:
• Deficit if Lesioned:

Answer 19

• **Function: **Distal limb coordination
• **Motor pathway influenced: **LCST, rubrospinal tract
• **Deficit if lesioned: **Appendicular ataxia

Question 20

1. **Vermis **
   
   • Function:
   • Motor pathway influenced:
   • Deficit if Lesioned:
2. Flocculonodular lobe
   
   • Function:
   • Motor pathway influenced:
   • Deficit if Lesioned:

Answer 20

1. **Vermis **
   
   • Function: Proximal limb & trunk coordination
   • Motor pathway influenced: VCST, reticulospinal tract, vestibulospinal tract
   • Deficit if Lesioned: Truncal ataxia
2. Flocculonodular lobe
   
   • Function: Balance & vestibuloocular reflexes
   • Motor pathway influenced: Medial longitudinal fasciculus
   • Deficit if Lesioned: Nystagmus/slow saccades

Question 21

Differential diagnosis for cerebellar dysfunction:

Answer 21

• Vestibular dysfunction
  
  • also causes vertigo, difficulty walking, N/V, nystagmus
  • usually no dysmetria or ataxia on finger to nose or heel to shin
• Corticospinal tract dysfunction
  
  • ​also causes hypotonia & weakness
  • can be mistaken for ataxia
• Impaired proprioception
  
  • these pts have a sensory ataxia
  • Ex: proprioceptive loss in feet makes walking difficult

Question 22

Acute causes for cerebellar dysfunctions:

Answer 22

1. Cerebellar stroke (ischemic or hemorrhagic)
2. Alcohol intoxication
3. Drug overdose (eg. phenytoin)
4. Multiple sclerosis

Question 23

Chronic causes for cerebellar dysfunctions:

Answer 23

1. Essential tremor
2. Spinocerebellar ataxia
3. Tumor (eg. astrocytoma)
4. Chronic alcoholism

Question 24

What can cause a cerebellar stroke?

Answer 24

Pathogenesis:

• main arteries supplying blood: SCA, PICA, AICA
  
  • diseased due to atherosclerosis
• penetrating arteries from the main arteries undergo arteriolosclerosis ⇒ blood flow compromised ⇒ ischemic stroke
  
  • ​from chronic HTN & other vascular risk factors (diabetes, smoking, high cholesterol)
• severe spike in blood pressure causes brittle vessel to rupture ⇒ hemorrhagic stroke

Question 25

What are some **clinical signs & symptoms** you expect to see from a cerebellar stroke? How would you **localize** them?

Answer 25

* **Sudden/acute onset** * within seconds to minutes * improves over weeks * **Symptoms** * inability to walk and frequent falls, nausea, vomiting, vertigo * **Signs** * **dysmetria of ipsilateral** arm/leg on finger-to-nose & heel-to-shin * mild **ipsilateral dysdiadochokinesia** * mild **dysarthria** * **horizontal & vertical nystagmus** * **Localization** * ipsilateral cerebellar hemisphere (lateral & flocculonodular lobes) & vermis * **Other clues for diagnosis:** vascular risk factors * HTN, smoking, diabetes, high cholesterol

Question 26

How can you differentiate between **chronic and acute alcohol intoxication affecting the cerebellum?**

Answer 26

**One of the most common causes of ataxia** * **Acute symptoms:** * inability to walk with frequent falls * no ‘checking’ of loss of balance * slurred speech * caused by **cerebellar neuronal dysfunction** * **Chronic symptoms:** * ataxia with walking/maintaining balance * difficulty with finger dexterity * caused by **Purkinje cell destruction** & **subsequent atrophy of vermis** * **Signs:** * difficulty walking/tandem gait, dysarthria, dysmetria of limbs, nystagmus * **Localization:** * cerebellar vermis

Question 27

What would you expect to see with an essential tremor? How is it localized?

Answer 27

**Most common movement disorder** * **Usually symmetric, bilateral, postural or action tremor** that is persistent & visible: * no other cause found * usually **autosomal dominant ** * involves arms/hands, voice, head * **chronic neurodegenerative disorder** * **gradual loss of Purkinje cells** * **Signs:** * dysmetria, ataxic gait, head titubation * **Localization:** * cerebellar hemispheres & vermis

Question 28

**Cerebellar ataxia:**

Answer 28

* Group of **autosomal dominant ataxic disorders** * degeneration of afferent & efferent cerebellar pathways * destruction of Purkinje cells * **CAG triplet repeat expansion** at different genetic loci * **Slowly progressive ataxia** of limbs/trunk, scanning speech, slowed saccades * **Profound cerebellar atrophy** * Higher morbidity & mortality than essential tremor * **Localization:** * entire cerebellum

Question 29

**Astrocytoma:**

Answer 29

**Most common childhood primary brain tumor** * low grade tumor composed of astrocytes * **Localization:** * tumor usually grows in cerebellar hemisphere * **Slowly progressive ipsilateral:** * limb/truncal ataxia, scanning speech, nystagmus due to tumor compressing on adjacent cerebellar parenchyma * **Signs of increased intracranial pressure** * **​morning headaches**, blurred vision, may culminate in nausea/vomiting, **difficulty concentrating in school** * **↑ICP occurs because of any lesion that takes up space in a closed calvarium**

Question 30

**What is multiple sclerosis?**

Answer 30

* **autoimmune/inflammatory disorder affecting CNS white matter** * Predilection for young (25-40’s), white females * Each lesion is referred to as a ‘plaque’

Question 31

**Which regions of white matter are attacked in a multiple sclerosis patient?**

Answer 31

**Regions of CNS that are attacked:** * **Optic nerves **⇒ causes sudden (over 1 day or so) vision loss * usually cloudy, hazy, blurry that improves over weeks * no double vision * **Cerebral white matter regions** * all tracts descending/ascending to cortex * **Cerebellar white matter** * especially the middle cerebellar peduncle * **Medial longitudinal fasciculus** * mediates eye movements * lesion causes internuclear ophthalmoplegia * **Spinal cord **⇒ complete or incomplete spinal cord lesion in transverse section affecting ascending/descending tracts * called a transverse myelitis