Patients with neurological disorders can pose a challenge for veterinary surgeons. It is indeed not uncommon to feel uncomfortable and unconfident when confronted with an animal with suspected neurological disease. Although several factors can be responsible for this 'neurophobia,' it is often wrongly assumed that all neurology patients need to be referred to a specialty centre for advanced and expensive diagnostics, such as magnetic resonance imaging (MRI). Not all neurology patients can however be referred, not all neurologically abnormal animals need to be referred, and not all referred patients will require advanced diagnostics. Whatever the underlying reason, 'neurophobia' - a fear of neurology and the neural sciences - can have clinical consequences.¹ It can hinder neurology education and hampers the clinician to develop a competent approach to patients with neurological disease.² Although patients with neurological disease can often present with spectacular clinical signs and emotionally distressed owners, the clinical approach to these patients is not necessarily different from animals affected by other disorders. The most important and cost-effective diagnostic tools in clinical neurology are the ears, hands, eyes, and brain of the clinician. The combination of a thorough clinical history, general physical examination, and neurological examination abnormalities will enable you to list the most likely differential diagnoses for the individual patient. This will serve as a starting point to discuss further diagnostics and management options with your client. A logical, problem-based approach will make confusing or intimidating presentations more manageable.

Diagnostic Approaches Not Suitable for Neurological Patients: Pattern Recognition and "Fishing"

Experienced veterinary surgeons can rely on pattern recognition to achieve most of their clinical diagnoses. This is especially true for common diseases with unique and specific clinical signs. This diagnostic approach becomes, however, problematic for less experienced clinicians, uncommon diseases or disorders characterized by unspecific clinical signs. Neurological disorders are particularly unsuitable for diagnosis by pattern recognition³; not the disease itself, but the location of the disease within the nervous system will dictate the nature of clinical signs.

This has two clinical consequences:

1.  Different diseases affecting the same location in the nervous system can cause the same clinical signs.

2.  A specific disease may affect different locations in the nervous system and can therefore present with variable clinical signs.

"Fishing" or performing a variable amount of diagnostic tests in the hope to find potential abnormalities, should also be considered less ideal in neurology patients. Routine diagnostic tests, such as haematology, biochemistry, and even analysis of cerebrospinal fluid are rarely specific for a given neurological disease. More specific neurodiagnostics are often more expensive and interpretation requires experience and training. Inappropriate selection of diagnostics can cause the owner to run out of money before a final diagnosis has been reached. "Fishing" for abnormal findings becomes also problematic when using the most sensitive neurodiagnostic procedure, MRI. Incidental and clinically irrelevant MRI abnormalities are commonly encountered in neurologically normal subjects. Differentiation between clinically relevant and irrelevant MRI abnormalities can be impossible without crucial information from a thorough neurological examination.⁴ You need to know what you're looking for before performing further diagnostics and consider which benefit you expect from specific diagnostics in an individual patient.

Problem-Based Clinical Reasoning

Problem-based clinical reasoning involves a logical progression through the following steps:

1.  Define the problem of your patient. This can include pain, a gait abnormality, seizures, or abnormal behaviour.

2.  Define which body system is affected. Neurological disorders can sometimes be difficult to differentiate from disorders affecting other body systems.

3.  Define the location of the problem. For neurological disorders this can include the forebrain, brainstem, cerebellum, spinal cord or peripheral neuromuscular disease.

4.  Define the lesion. Now a list of likely differential diagnoses should be obtained. The answers to questions (1), (2), and (3) are answered after obtaining a thorough clinical history (what is the actual complaint?) and performing a complete general physical and neurological examination. The primary aims of the neurological examination are to identify the neurological nature and the localisation within the nervous system of your patient's problem.

Define the Lesion - How to Get More From Your Neurological Examination

Traditionally, a list of differentials was obtained using the VITAMIN D or DAMNIT-V scheme. Many neurological diseases can, however, be divided in more than one of these categories and this system does not always allow you to narrow down your list of differentials to only the most likely disorders for your individual patient. More recent developments in medical education advocate a problem-based approach following the principles of clinical reasoning.⁵ More specifically, neurological disorders are associated with specific clinical characteristics and considering these specific clinical characteristics can be used to recognize the most likely differentials for an individual patient. After identifying the neuro-anatomical localisation, the most important clinical characteristics are (1) onset of clinical signs, (2) progression of clinical signs, (3) symmetry of clinical signs, (4) presence or absence of pain, and (5) patient's signalment. This diagnostic approach can also be referred to as the "5-finger-rule." Because identifying the neuro-anatomical localisation is the most important factor when considering the most likely differential diagnoses, this approach can also be expanded to the "6-finger-rule" with neuro-anatomical localisation being the sixth (or first) finger.

1. Neuroanatomical Localisation

Obtaining a neuroanatomical localisation is the starting point of obtaining a reliable list of differentials. Most neurological conditions will affect a specific or preferential part of the nervous system. How to obtain a neuroanatomical localisation is discussed in "Guide to the Neurological Examination.

2. Onset

The onset of clinical signs is typically divided into peracute, acute, and chronic. It is important to consider the difference between peracute (seconds to minutes) and acute (hours to days) onset of clinical signs. Although several neurological conditions are characterized by an acute onset of clinical signs, only a few are characterized by a peracute onset. Examples of disorders with a peracute onset are vascular (for example, a fibrocartilaginous embolism of the spinal cord) and idiopathic disorders (for example, idiopathic vestibular disease). Classical chronic conditions, such as neoplasia, can however also deteriorate acutely. This is referred to as "acute on chronic onset" of disease.

3. Progression

Progression of clinical signs can be divided into improving, static, deterioration, waxing and waning, and episodic. The presentation of 'spontaneously improving neurological signs' is more common than expected and can be seen in vascular disorders (for example, a cerebellar infarct), idiopathic disorders (for example, idiopathic Horner's syndrome), and pure contusive injuries (for example, acute non-compressive nucleus pulposus extrusion).

4. Symmetry

Clinical signs can be symmetrical or strongly lateralised (asymmetrical). Examples of strongly lateralized brain conditions are neoplasia and vascular disorders. Examples of strongly lateralized spinal cord conditions are fibrocartilaginous embolism and acute non-compressive nucleus pulposus extrusion (also referred to as high-velocity, low-volume disk extrusion or traumatic disk extrusion).

5. Pain

Neurological disorders, especially spinal disorders, can be painful. Presence of pain excludes several other conditions, such as degenerative myelopathy and fibrocartilaginous embolism. Animals with classical painful conditions, such as compressive intervertebral disk disease, are however not always overtly painful. These conditions should therefore not be excluded if no obvious pain can be elicited on spinal palpation.

6. Signalment

Neurological conditions commonly occurring in one species are very rare or not existent in other species. Different neurological conditions should therefore be considered in dogs and cats. Congenital and infectious disorders are more common in young animals, while neoplastic and degenerative conditions are more common in older animals. Neurological conditions can also be associated with gender and breed. Caution should however be exercised because not every neurologically abnormal Dachshund will have intervertebral disk disease. Problem-based clinical reasoning has recently been demonstrated to be valuable in the diagnostic approach of dogs with spinal disease and epilepsy.^6,7 It allows even inexperienced clinicians to obtain a reliable list of differentials in animals with neurological disease. It allows you to discuss specific diagnostic tests, treatment options and a realistic prognosis for the individual patient.

References

1.  Jozefowicz RF. Neurophobia: the fear of neurology among medical students. Arch Neurol. 1994;51:328–329.

2.  Schon F, Hart P, Fernandez C. Is clinical neurology really so difficult? J Neurol Neurosurg Psychiatry. 2002;72:557–559.

3.  Vickrey BG, Samuels MA, Ropper AH. How neurologists think. A cognitive psychology perspective on missed diagnoses. Ann Neurol .2010;67:425–433.

4.  De Decker S, Gielen IM, Duchateau L, et al. Intraobserver and interobserver agreement for results of low-field magnetic resonance imaging in dogs with and without clinical signs of disk-associated wobbler syndrome. J Am Vet Med Assoc. 2011;238:74–80.

5.  McColgan P, McKeown PP, Selai C, et al. Educational interventions in neurology: a comprehensive systematic review. Eur J Neurol. 2013;20:1006–1016.

6.  Armasu M, Packer RMA, Cook S, et al. An exploratory study using a statistical approach as a platform for clinical reasoning in canine epilepsy. Vet J.2014;202:292–296.

7.  Cardy TJA, De Decker S, Kenny PJ. Clinical reasoning in canine spinal disease: what combination of clinical signs is useful? Vet Rec. 2015;177:171.