Successful management of animals with suspected neurological disease can be a daunting and stressful prospect. It is however important to have a calm, structured, and logical approach when confronted with neurologically abnormal animals. A good understanding of the basic principles of the neurological examination is key to becoming more confident when evaluating neurological patients.

Before Performing a Neurological Examination

Although it is tempting to immediately perform a neurological examination, it is important to first obtain a detailed clinical history and perform a complete general physical examination. In several situations, the animal will be completely normal when presented to you. Examples of this are seizure and movement disorders. Information from the clinical history will then be the most important factor in selecting appropriate diagnostic and treatment options. Neurological abnormalities can also be caused by systemic diseases, which can only be recognized after a thorough general physical examination.

Why Performing a Neurological Examination?

After performing a complete neurological examination, you should be able to answer the following questions:

1.  Is the animal having a neurological disease?

2.  Which part of the nervous system is affected?

3.  And in selected cases, the results of the neurological examination will allow you to determine the prognosis of your patient.

Information retrieved from the neurological examination is crucial for obtaining a reliable list of differential diagnoses. After obtaining a list of the most likely differentials, appropriate diagnostic tests, treatment options, and prognosis for the individual animal can be discussed with the owner. Although several strategies can be used, a problem based approach, following the principles of clinical reasoning, is recommended. The concept of 'Clinical reasoning in veterinary clinical neurology' is discussed in "Neurology Without an MRI - What Can I Do?"

Basic Components of the Neurological Examination

The neurological examination can be divided in the hands-off and hands-on examination. The hands-off examination is unfortunately often overlooked. This part of the examination is however of great importance and often reveals key findings of your patient's neurological status. The neurological examination can be further divided into the following 7 components: (1) Mentation and behaviour, (2) Posture and gait, (3) Proprioception, (4) Cranial nerves, (5) Spinal reflexes, (6) Spinal palpation, and (7) Nociception. Parts (1) and (2) are evaluated during the hands-off examination. It is important to start with the least invasive parts of the neurological examination and progress further to the more invasive parts at the end of the neurological examination. Evaluating spinal pain and nociception/pain sensation can be considered the most invasive parts of the neurological examination.

1.  Mentation and behaviour: Abnormalities in mentation are often expressed as gradations of decreased mentation. The animal needs a stronger stimulus than normal to be aroused. Progressively decreasing levels of mentation are obtundation, stupor, and coma. Mentation can be decreased in forebrain and brainstem disorders. Examples of abnormal behaviour include circling, compulsive pacing, and head-pressing. Demonstration of abnormal behaviour is often suggestive of a forebrain disorder.

2.  Posture and gait: Abnormalities in posture include low-head carriage; kyphotic or arched back, which can be indicative of spinal pain; head tilt, which is suggestive of a vestibular disorder; and head-turn, which is suggestive of a forebrain disorder. Abnormalities in gait include paresis, ataxia, and lameness. It is important to realize that ataxia (= loss of coordination) and paresis (= weakness) are different concepts. Animals with ataxia can have cerebellar or vestibular disease, animals with paresis can have lower motor neuron disease, while animals with both ataxia and paresis can have spinal or brainstem disease.

3.  Proprioception: This is often evaluated by hopping or paw placement responses in dogs, while visual placing, tactile placing, and wheel barrowing are useful in cats. Proprioceptive deficits are a strong and reliable indicator for the presence of neurological disease. Proprioceptive deficits can occur in animals with forebrain, brainstem, and spinal disease, and are therefore not always useful for determining a more exact neuro-anatomical localization.

4.  Cranial nerves: Isolated cranial nerve deficits can be associated with specific idiopathic and often benign conditions. Certain combinations of cranial nerve deficits can be suggestive of vestibular or inner ear localisations, while multiple cranial nerve deficits can occur in brainstem disease or generalized lower motor neuron disorders.

5.  Spinal reflexes: Evaluation of spinal reflexes, such as the withdrawal reflex and patella reflex, is indicated to recognize focal or generalized lower motor neuron disease, and to evaluate which spinal cord segment is affected in animals with spinal cord disease.

6.  Spinal palpation: If the clinical presentation of the animal is suggestive for the presence of spinal pain, it is important to start with gentle palpation before applying deep palpation.

7.  Nociception: Because this part of the examination is unpleasant for the animal, evaluation of nociception or 'pain sensation' should only be performed in selected cases. It should only be performed in paraplegic (= all motor function is lost) and comatose animals. It is important to realize that the response of the withdrawal reflex and nociception have a different nature and should not be confused.

Determining the Neuro-Anatomical Localisation

The combination of clinical signs and findings of the neurological examination is used to determine the neuro-anatomical localisation. This will consist of one of the following: (1) forebrain, (2) cerebellum, (3) brainstem, (4) spinal cord, and (5) neuromuscular. The spinal cord is further divided into 4 functional spinal cord segments: C1-C5, C6-T2, T3-L3, and L4-S3 segments. Recognizing the correct neuro-anatomical localisation is important to obtain a list of the most likely differential diagnoses.

1.  Forebrain: Clinical signs include seizures, decreased mentation, abnormal behaviour, and central blindness. Additional abnormalities of the neurological examination include decreased menace response, decreased response after stimulation of the nasal mucosa, and proprioceptive deficits. In contrast to the situation in humans, forebrain disorders in small animals will generally not result in gait abnormalities. Obvious proprioceptive deficits in an animal with a normal gait can therefore be considered suggestive of a forebrain localisation.

2.  Cerebellum: Clinical signs include ataxia without paresis, hypermetria with overflexion of joints, central vestibular disease, and intention tremors. Cerebellar disorders are not associated with changes in mentation. Additional abnormalities of the neurological examination include decreased menace responses. Proprioception is typically not affected in pure cerebellar disease.

3.  Brainstem: Clinical signs include facial abnormalities, decreased mentation, generalised ataxia, hemiparesis, tetraparesis, and vestibular disease. Additional abnormalities of the neurological examination include proprioceptive deficits and cranial nerve deficits.

4.  Spinal cord: Clinical signs can include a combination of ataxia and paresis, spinal hyperesthesia, and bladder dysfunction. Additional abnormalities of the neurological examination include proprioceptive deficits and alterations in spinal reflexes. Further classification into any of the 4 functional spinal cord segments is based on the number of affected limbs (tetra- or para-) and the presence of intact, increased, or decreased spinal reflexes. Decreased or absent spinal reflexes indicate a lesion in the intumescence (C6-T2 or L4-S3 spinal cord segments).

5.  Neuromuscular: The hallmark of neuromuscular disease is paresis without ataxia. Paresis in animals with neuromuscular disease can vary from exercise intolerance to flaccid tetraplegia. Other clinical signs include changes in voice and regurgitation. Additional abnormalities of the neurological examination can include decreased spinal reflexes and cranial nerve deficits. Although neuromuscular disorders will typically not result in neurological deficits, affected animals can be too weak to correct abnormal paw placement.

Determining Prognosis

Although prognosis for an individual animal is largely dependent on the specific diagnosis, the neurological examination can provide prognostic information in selected cases. Loss of nociception or pain sensation is the most important clinical prognostic factor in animals with spinal disease. Although loss of nociception is considered an indicator of poor prognosis, it is still dependent on the specific diagnosis. Prognosis in animals with loss of deep pain sensation is better for animals with acute intervertebral disk disease compared to animals with a spinal fracture or luxation. Negative prognostic factors for animals with traumatic brain injury are bilateral mydriatic pupils with negative pupillary light reflexes, decerebrate rigidity, and a prolonged comatose mental status. A comatose mental status is defined as decreased mentation in which the animal is no longer responsive to painful stimuli.