Q 1.7. Cordination and the Cerebellum

Anatomy and Physiology of the Cerebellum:

• The cerebellum, often referred to as the “little brain,” plays a crucial role in motor control.
• It is located at the back of the brain, inferior to the occipital and temporal lobes, within the posterior cranial fossa.
• The cerebellum consists of two hemispheres connected by the vermis (a narrow midline area).
• Its structure includes:
  • Grey matter: Forms the cerebellar cortex, tightly folded on the surface.
  • White matter: Lies beneath the cortex and contains the four cerebellar nuclei (dentate, emboliform, globose, and fastigi nuclei).
• The cerebellum coordinates voluntary movements, precision, timing, and motor learning.

Major Connections of the Cerebellum:

1. Middle Cerebellar Peduncle (MCP):
   • Connects the cerebellum to the brain stem (pons).
   • Carries axons projecting from the gray matter of the pons into the contralateral cerebellar cortex.
2. Superior Cerebellar Peduncle (SCP):
   • Connects the cerebellum to the midbrain and forebrain.
   • Involved in maintaining balance and posture.
3. Inferior Cerebellar Peduncle (ICP):
   • Connects the cerebellum to the medulla.
   • Conveys sensory input to the cerebellum, including information from the spinocerebellar tract.

Examination and symptoms of cerebellar lesions:

Finger-to-Nose Test (FNT)

The Finger-to-Nose Test is a neurological examination used to assess cerebellar function, specifically coordination and proprioception. It is a simple yet effective test that can reveal abnormalities in the central nervous system.

Procedure:

1. The patient is asked to fully extend their arm.
2. Then, they must touch their nose with the tip of their index finger.
3. The patient repeats this action several times, usually with both arms.
4. The examiner may increase the difficulty by adding resistance or moving their finger to different locations for the patient to touch before touching their nose.

Normal Response:

• The patient should be able to touch their nose smoothly and accurately without any tremors or hesitation.

Abnormalities:

• Dysmetria: This is the primary abnormality detected by the FNT. It is characterized by the inability to judge the range of movement needed to meet the target (the nose or the examiner’s finger). Patients may undershoot (hypometria) or overshoot (hypermetria) the target.
• Intention Tremor: A tremor that becomes more pronounced as the patient’s finger approaches the target. It indicates a lesion in the cerebellum.
• Past-Pointing: Consistent deviation to one side when attempting to touch the target, which may suggest a lateralized cerebellar lesion.

Clinical Significance: The FNT is particularly useful in diagnosing conditions such as cerebellar ataxia, multiple sclerosis, and other disorders that affect coordination. It is a quick test that can be performed at the bedside or in an outpatient setting and provides valuable information about the integrity of the cerebellar pathways.

 

Heel-to-Knee Test

The Heel-to-Knee Test, also known as the Heel-to-Shin Test, is a clinical examination maneuver used to assess coordination and function of the cerebellum. It is particularly useful for identifying cerebellar ataxia.

Procedure:

1. The patient is either sitting or lying down with their legs extended.
2. The patient is asked to place the heel of one foot on the knee of the opposite leg.
3. Then, they slide the heel down the shin to the ankle.
4. This action is repeated several times for each leg.

Normal Response:

• The patient should be able to perform the movement smoothly and without difficulty, maintaining contact between the heel and the shin throughout the motion.

Abnormal Findings:

• The heel may overshoot the knee or fall to either side of the shin as it descends the opposite leg.
• The heel may be held elevated above the leg (not in contact) in a patient with lost proprioception.
• These abnormalities suggest cerebellar disease and may indicate issues such as cerebellar ataxia or other cerebellar lesions.

Clinical Significance: The Heel-to-Knee Test is a simple yet effective way to evaluate the cerebellum’s ability to coordinate fine motor movements. It is often included in a comprehensive neurological examination and can provide insight into the presence of cerebellar dysfunction.

 

Diadochokinesia Test

The Diadochokinesia Test assesses an individual’s ability to perform rapid, alternating movements, which is a key aspect of cerebellar function. This test is crucial for identifying dysdiadochokinesia, a condition characterized by the inability to make rapid, alternating movements smoothly.

Procedure:

1. The patient is asked to perform rapid, alternating movements with their hands, such as pronation and supination (turning the palms down and up).
2. The patient may also be asked to tap their foot quickly or perform rapid alternating movements with their fingers.
3. The examiner observes for smoothness, rhythm, and speed of the movements.

Normal Response:

• The patient should be able to perform these movements rapidly and with a regular rhythm without difficulty.

Abnormal Findings:

• Dysdiadochokinesia: Difficulty in performing these movements, which may appear slow, irregular, or clumsy. This is often due to cerebellar dysfunction.
• Delayed Initiation: A delay in starting the movement, which may indicate a lesion in the cerebellum or associated pathways.
• Incoordination: Lack of coordination between agonist and antagonist muscles, leading to jerky or uncontrolled movements.

Clinical Significance: The Diadochokinesia Test is a simple yet effective way to evaluate the cerebellum’s ability to coordinate rapid, alternating movements. It can help identify cerebellar lesions and is often used in the diagnosis of conditions like multiple sclerosis, cerebellar ataxia, and other disorders affecting motor control.

 

Stewart-Holmes Test

The Stewart-Holmes test evaluates the integrity of the cerebellum, which is responsible for fine-tuning motor activity and coordinating movement.

Procedure:

1. The patient is asked to flex their arm and clench their wrist.
2. The examiner grips the patient’s wrist and applies resistance, asking the patient to resist the pull.
3. Suddenly, the examiner releases the grip on the patient’s wrist.
4. The patient’s ability to control the rebound movement of the arm is observed.

Normal Response:

• The patient’s antagonist muscles should contract to stop the arm from moving further, demonstrating good rebound control.

Abnormal Findings:

• If the patient fails to control the rebound and the arm continues moving in the direction it was pulled, it could indicate damage to the cerebellum.
• The examiner must be cautious to protect the patient from potential injury during the test.

Clinical Significance: The Stewart-Holmes test is particularly useful for identifying cerebellar disease. It helps to differentiate between cerebellar and other neurological disorders by assessing the cerebellum’s ability to modulate and correct motor action.

 

The Romberg Test is a neurological test that assesses the integration of sensory input from proprioception (the sense of body position) and vestibular function (balance) for maintaining an upright stance. While it is not a direct test of cerebellar function, it can provide indirect information about cerebellar lesions.

Procedure:

1. The patient stands with their feet together and arms by their sides.
2. They are asked to maintain this position first with their eyes open, and then with their eyes closed.
3. The examiner observes for any swaying or loss of balance.

Normal Response:

• The patient should be able to stand steadily with minimal sway, both with eyes open and closed.

Abnormal Findings:

• A positive Romberg sign is when a patient sways or falls upon closing their eyes, which indicates a sensory ataxia due to a proprioceptive deficit.
• While the Romberg Test is not a sign of cerebellar disease, patients with cerebellar lesions may exhibit increased sway with eyes closed. However, this is due to the cerebellum’s role in integrating sensory information and coordinating movement, rather than a direct indication of cerebellar dysfunction.

Importance in Cerebellar Lesion:

• The importance of the Romberg Test in the context of cerebellar lesions lies in its ability to differentiate between sensory ataxia and cerebellar ataxia. Patients with cerebellar ataxia may show a wide-based gait and may sway more with eyes closed, but they do not typically fall, as they can still rely on their vestibular input and visual cues when their eyes are open.

Clinical Significance:

• The Romberg Test is an essential part of the neurological examination as it helps in identifying the underlying cause of balance disorders. It is particularly significant in distinguishing between different types of ataxia and understanding their relation to cerebellar lesions.

 

Speech Impairment in Cerebellar Lesions

The cerebellum plays a crucial role in the coordination and timing of motor activities, including speech. Lesions in the cerebellum can lead to a variety of speech impairments, collectively known as ataxic dysarthria.

Characteristics of Ataxic Dysarthria:

• Irregular Articulation: Speech may be slurred or scanning, with irregular emphasis on syllables.
• Prosody Changes: The rhythm and melody of speech may be disrupted, leading to monotonous tone or inappropriate stresses.
• Vocal Quality: The voice may sound harsh or strained, and there may be fluctuations in volume.
• Rate of Speech: Speech may be slow with prolonged phonemes and pauses between words or syllables.

 

Writing Changes in Cerebellar Lesions vs. Parkinson’s Disease

Cerebellar Lesions:

• Writing may become large and erratic.
• Patients may exhibit decreased control over the size and shape of letters.
• Writing can be irregular with varying letter sizes and inconsistent spacing between words.
• The hand may overshoot or undershoot when writing, a manifestation of dysmetria.
• There may be tremulousness in the strokes due to intention tremor.

Parkinson’s Disease:

• Writing often becomes smaller, a condition known as micrographia.
• Patients may start writing at a normal size, but the size decreases progressively, a phenomenon called progressive micrographia.
• The writing speed may slow down, and the pressure applied by the pen may become lighter.
• Letters and words may be crowded together, and there can be a tremor in the writing, especially at the beginning of writing tasks.

Clinical Significance:

• These changes in writing are important diagnostic clues.
• In cerebellar lesions, the lack of coordination leads to erratic and inconsistent writing patterns.
• In Parkinson’s disease, the bradykinesia and rigidity contribute to the characteristic small and cramped handwriting.

 

Muscle Tone Changes in Cerebellar Lesions

Muscle tone refers to the resistance of muscles to passive movement. It is an important indicator of the integrity of the motor system, including the cerebellum.

Cerebellar Lesions:

• The cerebellum contributes to the regulation of muscle tone through its connections with motor pathways.
• Lesions in the cerebellum can lead to hypotonia, which is a decrease in muscle tone.
• Hypotonia may be observed as a reduced resistance to passive movement of joints during a physical examination.
• However, the ability to detect reduced muscle tone is highly subjective and can feel ‘normal’ in cerebellar disease.
• In severe cerebellar damage, hypotonia is usually more pronounced and can be accompanied by other cerebellar signs.

 

Nystagmus is an involuntary, rhythmic oscillation of the eyes that can be a sign of various neurological conditions, including cerebellar and peripheral vestibular lesions. Understanding the characteristics and types of nystagmus is crucial for medical students when diagnosing and differentiating between these conditions.

Types of Nystagmus in Cerebellar Lesions:

• Gaze-Evoked Nystagmus (GEN): Occurs when the patient’s gaze is directed to the side and is unable to maintain a stable position, resulting in rhythmic jerking back to the central position.
• Downbeat Nystagmus: Characterized by a downward fast phase, often associated with lesions in the flocculus or nodulus of the cerebellum.
• Upbeat Nystagmus: Involves an upward fast phase and may be caused by lesions affecting the medulla or midbrain.
• Rebound Nystagmus: After maintaining an eccentric gaze, the eyes drift back towards the eccentric position before correcting themselves when the patient looks back to the center.

Distinguishing Cerebellar from Peripheral Vestibular Nystagmus:

• Peripheral Vestibular Nystagmus:

  • Often presents with a horizontal or horizontal-torsional pattern.
  • The fast phase of the nystagmus beats away from the side of the lesion.
  • It is typically inhibited by visual fixation.
  • The intensity of the nystagmus can change with the direction of gaze, increasing when looking away from the affected side.

• Cerebellar Nystagmus:

  • Can present with horizontal, vertical, or torsional nystagmus.
  • Does not typically change with gaze direction or visual fixation.
  • Often accompanied by other cerebellar signs such as dysmetria, ataxia, or dysarthria.
  • Gaze-evoked nystagmus in all directions is indicative of cerebellar dysfunction.

 

Coordination Impairments and Ataxia:

• Ataxia refers to poor muscle control resulting in clumsy movements.
• Causes of ataxia include:
  • Damage to the cerebellum (e.g., stroke, multiple sclerosis).
  • Underlying conditions (e.g., hypothyroidism, vitamin E deficiency, brain tumors).
  • Hereditary disorders (e.g., Friedreich ataxia).
  • Autoimmune reactions (subacute cerebellar degeneration).
• Common types of gait abnormalities:
  • Propulsive gait (Parkinsonian gait): Stooping posture, short steps.
  • Scissors gait: Knees and thighs cross during walking.
  • Spastic gait (hemiplegic gait, Wernicke-Mann): Stiff leg, dragging or circumduction.
  • Steppage gait (neuropathic gait): High step, floppy foot.
  • Ataxic Gait (Cerebellar Gait): Most commonly seen in cerebellar disease, this gait is described as clumsy, staggering movements with a wide-based stance.

 

DANISH Mnemonic for Cerebellar Lesions

When assessing for cerebellar lesions, the mnemonic DANISH can be extremely useful for recalling the common symptoms associated with cerebellar dysfunction:

• D – Dysdiadochokinesia: Difficulty in performing rapid alternating movements.
• A – Ataxia: Lack of voluntary coordination of muscle movements, evident in gait and posture.
• N – Nystagmus: Involuntary eye movement, which may be horizontal, vertical, or rotary.
• I – Intention Tremor: A tremor that occurs during voluntary movements towards a target.
• S – Slurred Speech: Changes in speech articulation, often described as staccato or scanning speech.
• H – Hypotonia: Decreased muscle tone, which can be assessed through the heel-shin test.

 

References:

1 oxfordmedicaleducation.com 

2 stanfordmedicine25.stanford.edu

3 WebMD.com

4 link.springer.com