Differentiating between causes of gait abnormalities in practice can be challenging.¹ However, by initially defining the problem and the system involved, a list of further appropriate diagnostic tests can be performed. Despite the recent advances in diagnostic imaging, the neurological and orthopaedic examinations remain the foundation of localising the lesion and help identified severity. The majority of cats and dogs that present with a thoracic or pelvic limb lameness will have an underlying orthopaedic condition, but it is important to recognise that neurological disorders can present with similar clinical signs. Neurological disorders will more commonly present as decreased voluntary movement (paresis) or lack of voluntary movement (plegia), these clinical signs are not synonymous with neurological disorders. Once the location of the lesion has been defined, a list of differential diagnoses can be formulated based on onset, clinical course and clinical features such as pain and asymmetry of clinical signs (five finger rule) plus signalment. Each individual case has its own challenges, and any purely rule-based system is likely to result in mistakes. I will discuss various cases and have a live, on-stage discussions which I hope will help you tackle these challenging cases better in the future.

The majority of patients who present with gait abnormalities will have abnormalities that primarily and structurally affect either the musculoskeletal or the nervous systems. As a result, lesion localisation will concentrate on lesions affecting the musculoskeletal and neurological systems. Unlike the cardiovascular, metabolic and respiratory body systems, there is no simple laboratory or diagnostic test that can be performed to differentiate between the nervous and musculoskeletal body systems. The differentiation between the two systems is based on the clinician’s physical examination. Most animals with neurological disorders will present with paresis, while those with orthopaedic disorders will present with lameness.

For neurological diseases it is important to differentiate between diseases which cause only pain and no neurological deficits (painful non-myelopathic spinal diseases) and diseases which cause neurological deficits (myelopathic spinal diseases).

Non-myelopathic Spinal Diseases

Animals that solely present with back pain and do not show neurological deficits need to have a thorough orthopaedic examination, as polyarthritis has to be considered. Other differentials are inflammatory, infectious, and neoplastic diseases. If the animal presents with a history of trauma, luxation and fractures need to be considered. As aforementioned, syringomyelia is an exception and can present as a painful condition without causing neurological deficits.

Myelopathic Spinal Diseases

The five-finger rule (onset, progression, pain, lateralisation and neuroanatomical localisation) can be used to effectively differentiate between myelopathies these myelopathies. A couple of examples are listed as follows:²

• Patients who present with peracute, non-progressive or improving, largely non-painful and lateralised neurological deficits have a 98% chance of having an ischaemic myelopathy such as fibrocartilaginous embolism (FCE) or acute nucleus pulposus extrusion (high velocity but low volume disc extrusion/traumatic disc).
• Hansen type-I disc disease (intervertebral disc extrusion) is best characterised as an acute onset, deteriorating, painful and occasionally lateralised myelopathy. Ninety percent of patients presenting with these clinical signs will have Hansen type-I disease.
• In contrast, Hansen type-II (intervertebral disc protrusion) has a more chronic onset, is often stable, but still painful. Meningo(encephalo)myelitis of unknown aetiology (MUA) can present with an acute onset, deteriorating painful myelopathy. MUA is four times more likely to present as a multifocal neuroanatomical localisation (multiple spinal cord segments and/or brain). Many of the animals will also have mentation changes and cranial nerve deficits.

These examples demonstrate that thinking pathophysiologically and using the five-finger rule can refine the differential list significantly. If you then also take demographics and signalment into account, you have a very high chance of identifying the most likely diagnosis before embarking on diagnostics. Many of the neurological conditions will require advanced imaging and/or CSF analysis, but funds are limited, and the aforementioned approach can provide you with the framework to narrow down diagnostics to the most essential or provide the owner with a presumptive diagnosis.

References

1.  Maddison JE, Volk HA, Church DB. Clinical Reasoning in Small Animal Practice. Wiley Blackwell; 2015.

2.  Cardy TJ, De Decker S, Kenny PJ, Volk HA. Clinical reasoning in canine spinal disease: what combination of clinical information is useful? Vet Rec. 2015;177(7):171.