Equine Nervous System Examination (Neuro 1)

Equine Nervous System Examination (Neuro 1)

• Objectives:
  • Students will demonstrate competence in performing neurological examinations on horses.
  • Focus on localization, personnel safety, and biosecurity.
  • Include spinal ataxia and grading schemes.
  • Include cranial nerves.
  • Knowledge of Horner's syndrome pathophysiology and diagnosis.

When to Perform a Neurological Examination

• Necessity: Is neurological disease present? If so, where is the process localized in the nervous system?
• Evaluation: Use "snapshots" of the disease and repeated examinations to determine progression and prognosis.
• Limitations: Subjective assessments, subtle personality/mentation changes might be undetectable. Consider owner input, normal ranges for age and breed, sedative effects, and alpha 2 agonists.

Information to Gather

• Chief Complaint: Seizures, weakness, won't hold up leg, cross-canters behind, unexplained wounds, or clumsiness.
• Signalment: Species, breed, and age.
• History: Define the clinical course and treatments/diagnostics performed up to this point.
• Physical Examination: Incorporate systemic disease evaluations that may induce neurologic symptoms.

Assessment of Mentation and Behavior

• Observation: Observe animal during history taking or video review. Note fear, anxiety, aggression, dullness, obtundation, stupor, and unconsciousness.
• Clinical Neuroanatomy:
  • Mental awareness is a function of higher brain centers (dullness < lethargy < obtundation < stupor < coma).
  • Sensory information reaches consciousness in the cerebral cortex leading to initiated voluntary movements.
  • Ascending reticular activating system (ARAS) plays a key role; sensory information travels to the cortex through the ARAS pathways.

Assessment of Posture

• Observation: Examine head/limb positioning in space. Observe for strabismus, nystagmus, and blindness (commonly linked to vestibular diseases).
• Head Tilt: This is a crucial indicator for many types of diseases.
• Head Turn: Cerebral and thalamic lesions typically manifest as head turns towards the affected side.

Assessment of Posture (cont'd)

• Schiff-Sherrington Syndrome: Forelimb extensor rigidity without opisthotonus.
• Opisthotonus: Head and neck in extreme extension.
• Midbrain Disease: Decerebrate rigidity impacting all limbs.
• Cerebellar Disease: Decerebellate rigidity, typically affecting just the forelimbs, often accompanied by intention tremors.
• Spinal Ataxia: Evidence of base wide stance, knuckling, sway, and dog-tracking.

Localizing the Lesion

• Mental Change: Implicates cerebral involvement.
• Intention Tremors: Suggest cerebellar issues.
• Ataxia without Mental Change: Likely spinal involvement.
  • Hind limbs alone indicate thoracolumbar or sacral spinal problems.
  • Front and hind limbs (or hind limbs worse than front) indicate cervical or thoracic intumescence.
  • No limb reflexes are possible.
  • Difficult to differentiate upper and lower motor neuron diseases.

Cranial Nerves

• Number: 12 pairs.
• Innervation: Innervates head structures; ipsilaterally (same side).
• Origination: Many originate in the brainstem, except for CN I and CN II.
• Evaluation: Check your 1604 lecture notes or the Hahn paper.
• Organization: Numerical and functional groupings are helpful.

Localizing Lesions in the Visual Pathway

• Optic Nerve/Primary Eye Issues: Both vision and pupils-light reflexes (PLR) are abnormal.
• Cortical Lesions: Vision is affected, but PLR is normal.
• Efferent Arms Lesions: Vision is normal, but PLR is abnormal.
• Important takeaway: One can be blind but have normal PLR.

Sympathetic Innervation to the Eye

• Function: Responsible for pupil dilation, eyelid retraction, and globe protrusion.
• Horner's Syndrome: Results from disrupted sympathetic innervation to the globe/periorbital area.
• Clinical Signs: Common signs include ptosis, miosis, enophthalmos, and potential third eyelid protrusion, and ipsilateral facial and neck sweating.

Horner's Syndrome (cont'd)

• Guttural Pouch/Cranial Cervical Ganglion Lesions: Cause face and cranial neck sweating.
• Sympathetic Trunk Lesions (Neck): Cause face and neck sweating (C3-C4).
• Thoracic Inlet Lesions: Potential for sweating in areas down to the shoulder.

Anisocoria (Unequal Pupils)

• Evaluation: Darkened room, observe pupil dilation in dim light.
• Normal Response: Equal dilation.
• Abnormal Response: Indicates possible CN III or Horner's syndrome.
• Diagnosis: The pupil that's smaller is abnormal.

Reflexes

• General: Many are limited to recumbent animals, as opposed to standing ones (e.g. patellar reflex).
• Hyperreflexia: Usually suggests an upper motor neuron issue.
• Hyporeflexia: Typically points to a lower motor neuron problem.
• Panniculus/Cutaneous Trunci Reflex: "Fly twitch." Absent with lesions anywhere above the test point in the spinal pathway.
• Other Reflexes: Cervico-facial, lordosis/kyphosis, perianal and anal tone, and lateral thoracic.

Neck Stretching

• Evaluation: Subjective assessment of neck flexibility, stiffness, and potential pain.

Abnormalities of Gait

• Spinal Ataxia: The faster the horse travels, the more normal its gait appears.
• Hypermetria: Excessive limb lifting (upper motor neuron).
• Hypometria: Weakness and dragging of limbs (lower motor neuron).
• Intention Tremors: Easily observed during feeding or other situations. Linked to cerebellar disease.

Spinal Ataxia (Grading)

• Grade 0: Normal.
• Grade 1: Extremely mildly affected; performance limiting needing multiple tests.
• Grade 2: Mildly affected; performance limit; observable to a professional.
• Grade 3: Obvious abnormality to a layman, even at rest.
• Grade 4: Significantly ataxic; may fall during exams. Dangerous.
• Grade 5: Recumbent; unable to stand; extremely dangerous.

Walking/Gait Assessments

• Straight Line: Observe cadence/consistency, foot placement, and limb flight consistency.
• Circles: Observe pivoting, circumduction, limb flight height, toe dragging and other deviations.
• Trotting: Assess cadence/consistency, foot placement, and limb flight consistency.
• Cantering: Observe if the 3-beat gait pattern is maintained (common for faster horses to deviate slightly).
• Racetrack is a helpful comparison for gait norms

Tail Pull Reflex

• Initiation: Stand horse; pull tail to elicit extensor reflex.
• Significance: A poorly executed reflex suggests a lower motor neuron lesion at L3-L5.
• Subjective Assessment: Assess strength and learning during the exercise.

Walking with Head Elevated

• Normal Response: Normal horses continue walking without any alterations.
• Abnormal Response: Abnormal horses may demonstrate cat-walking or try to look. Removes visual compensation affecting the gait.

Placements (Proprioception Assessment)

• Theoretical Test: Places, hops. Use is not prevalent anymore, theoretical tests of proprioception.
• Alternative Tests: These types of tests are not conducted regularly anymore.

Obstacles (Hills/Curbs)

• Proprioception Test: Evaluate how horses navigate hills/curbs; not frequently used in current practice.
• Clumsiness Variation: Some horses are naturally clumsy, making some tests less useful.

Autonomous Zone

• Importance in Uneven Limb Conditions: Importance when only one limb is affected.
• Radial Nerve Specificity: Radial nerve doesn't have a consistently defined zone in all horses.