Chapter 1
'Is it Neurological?'

Paul M. Freeman

The first step to any neurological evaluation of a veterinary patient, and probably the most common question we are asked by practitioners (in a variety of different ways), is whether the problem facing them is partially or completely neurological. In order to answer this question, it is important to understand the nature of the problem from the point of view of both the animal and the owner, and furthermore to understand what is meant by the question 'Is it neurological?'. For example, when presented with a dog that is showing signs of exercise intolerance, one possible reason may be a neuromuscular disorder, such as myasthenia gravis. However, this dog may present with a completely normal neurological examination, and the clue may be in the presenting clinical signs or medical work-up. Therefore, in such a case the initial answer may have to be 'It might be'. A dog whose problem is intermittent 'episodes' of abnormal behaviour may be having seizures, but might also be suffering from syncope, a compulsive behavioural disorder, or a movement disorder. All of these possibilities may in some way be classified as 'neurological' problems, but with very different aetiologies, treatment possibilities, and prognoses. The goal of this book is to allow practising vets to feel confident that they are approaching potentially neurological problems in a reasonable and evidence-supported way. The first step in this process is learning how to recognise when a particular presentation may be caused by a disease process somewhere within the central nervous system (CNS) or the peripheral nervous system (PNS).

1.1 What Is the Problem?

One of the key skills to be developed in general practice, as well as referral practice, is learning how to control the consultation in order to establish what the client's primary concern is, what they hope to achieve from their visit with you as the veterinarian, and how their expectations match up to their ability and/or willingness to afford and allow potential investigations and/or treatments to be performed. This is not an easy skill, especially for the GP vet who may have very limited time in which to carry out the initial consultation. It is, however, key to both ultimate client satisfaction and to providing the most effective service to the animal patient. Without establishing these essential facts, much time can be wasted. In the worst case the client's real concerns may not be addressed at all, meaning that they may leave the practice dissatisfied, perhaps with good reason.

Top tip: Always ask the client directly why they have come to see you today.

Don't make this mistake: Take care not to become side-tracked by a problem which may be very interesting to you, but is possibly chronic and completely unrelated to the reason for the visit!

1.2 Is this Problem Neurological?

There are many possible manifestations of neurological disease, some of which are much easier to recognise as neurological than others. There are also many non-neurological diseases which can mimic a problem involving the nervous system. In this section, we will look at the scope of neurological disease manifestations that the clinician may be presented with and we will aim to provide some clues as to the correct recognition of neurological disorders.

1.3 Neuroanatomy

When attempting to decide whether the problem is neurological, it is important to be aware of the different parts of the nervous system and how disease processes may affect them. Broadly we are concerned with the CNS (the brain and spinal cord) and the PNS (consisting of the peripheral nerves and muscles and the neuromuscular junctions between them). In the brain we can generally distinguish clinical signs referable to the forebrain, the brainstem, and the cerebellum.

The forebrain is known as the prosencephalon, and can be further divided into the telencephalon, which consists of the cerebral hemispheres, and diencephalon, containing the thalamus and the hypothalamus. The group of clinical signs which are commonly caused by lesions affecting the forebrain are sometimes referred to as a prosencephalic syndrome, and include behavioural change, central blindness, and seizure disorders in particular.

The brainstem consists of the midbrain (mesencephalon), the pons (ventral metencephalon), and the medulla (myelencephalon). Disease of the brainstem also leads to characteristic signs, which can be used to anatomically localise the problem, including proprioceptive deficits and ataxia, sometimes clusters of cranial nerve signs, vestibular syndrome, and mentation change associated with dysfunction of the ascending reticular activating system.

The third major division of the brain is the cerebellum (dorsal metencephalon), and lesions in this region can lead to some of the most recognisable abnormalities in the neurological examination, including hypermetria and intention tremor.

The medulla is contiguous with the spinal cord, which can be divided into a series of segments from which a pair of spinal nerve roots arises, one pair for each segment. For neuroanatomical localisation purposes, the spinal cord segments are grouped together according to their motor function, and whether or not they contain the cell bodies of the nerves which directly supply the skeletal muscles of the limbs (known as lower motor neurons, LMNs). In this regard, the first five cervical spinal segments (C1-C5) contain only the so-called upper motor neurons (UMNs) which run from the gait-generating centres of the cerebral cortex and brainstem to the LMNs innervating the limbs and other structures. Spinal cord lesions affecting segments in this region lead to a characteristic set of neurological examination findings involving UMN effects in all four limbs.

The sixth, seventh, and eighth cervical segments, along with the first two thoracic segments, C6-T2, contain the LMN cell bodies supplying the thoracic limbs, as well as UMNs to the pelvic limbs; lesions here cause a so-called LMN paresis or plegia (paralysis) of thoracic limbs and an UMN paresis/plegia of the pelvic limbs.

Lesions in spinal segments caudal to the second thoracic segment will generally only affect the pelvic limbs, and the division between UMN and LMN here occurs between the third and fourth lumbar segments. Hence, lesions affecting the T3-L3 spinal cord segments lead to UMN paresis of pelvic limbs, whereas lesions caudal to L3 (L4-S3) cause LMN paresis/plegia of the pelvic limbs.

As well as the descending motor tracts within the spinal cord, there are of course ascending sensory tracts including those carrying proprioceptive information from the limbs and trunk; therefore, a spinal cord disorder will usually lead to variable degrees of ataxia and proprioceptive dysfunction, as well as the paresis associated with the loss of motor function.

The final part of the nervous system within which we can make an anatomical localisation consists of the peripheral nerves, neuromuscular junctions, and muscles. Lesions affecting this neuromuscular system tend to lead to more obvious weakness and LMN paresis/plegia affecting all limbs. Therefore, syndromes such as weakness, stiffness, exercise intolerance, and collapse may all arise as a result of disease affecting this PNS.

The neurological examination and neuroanatomical localisation of specific lesions will be explored and explained in more detail in Chapters 3 and 4, but an understanding of the anatomical structures involved in neurological disorders is an essential part of the ability to recognise when one is facing a neurological problem (see Figure 1.1).

Figure 1.1 Neuroanatomical regions. The aim of the neurological examination is to localise the site of a lesion into the brain, the spinal cord, or peripheral (neuromuscular) regions. Functionally, the brain is separated into the forebrain, brainstem, and cerebellum; the spinal cord into sections containing the segments 1st cervical - 5th cervical (C1-C5), 6th cervical - 2nd thoracic (C6-T2), 3rd thoracic - 3rd lumbar (T3-L3), and 4th lumbar - sacral (L4-S3); and the peripheral nervous system consists of peripheral nerves, with the neuromuscular junctions and muscles also considered as a potential neuroanatomical localisation.

1.4 Manifestations of Diseases of the Nervous System

Disorders that affect different parts of the nervous system may manifest themselves in a wide variety of ways. In this section, we will briefly look at each of these, with the most important and more common problems being examined in greater detail in Chapter 6. The majority of nervous system disease will result in one or more of the following clinical presentations, some of which can be more easily defined and recognised than others. Where relevant, non-neurological disorders that can mimic or also result in these clinical presentations will also be mentioned:

• seizures
• collapse
• movement disorder/dyskinesia
• mentation change
• behaviour change
• blindness
• deafness
• tremor
• paresis/plegia
• ataxia
• abnormality of head position (head tilt/turn)
• abnormality of eye position or...