Differential Diagnosis

The simplest approach to a case with neurologic signs, once the lesion is localized, is to consider differential diagnoses using the acronym lists based on pathophysiologic mechanisms. These acronyms are called either VITAMIN-D or DAMNIT-V and are very useful and practical ways to approach neurologic diseases. A list of common diseases according to the VITAMIN-D acronym is presented in Table 4.1 and Table 4.2, and Fig. 4.1 and Fig. 4.2. When using this acronym, it is useful to consider the signalment and history to develop appropriate differential diagnoses for the patient. For example, even though intervertebral disc disease is the most common spinal disease of dogs, it is not a reasonable differential diagnosis for a 6-mo-old dog with chronic paraparesis. Some generalities should be considered when using the VITAMIN-D acronym. Young dogs are more likely to have congenital or inflammatory conditions. Acute presentations are usually caused by vascular or traumatic conditions. Chronic presentations are usually seen with degenerative or neoplastic processes. Another way to approach patients with neurologic problems is to develop a list of diseases that are known to affect specific regions of the brain and spine. This is useful mainly for spinal disorders, because although many diseases affect several spinal regions (e.g. intervertebral disc disease, discospondylitis, fibrocartilaginous embolic myelopathy), many are region-specific (e.g. atlantoaxial instability, cervical spondylomyelopathy, degenerative myelopathy). The primary differential diagnoses for the most common diseases affecting each region of the brain and spine are presented in Tables 4.3–4.9. Some of the diseases listed are presented in only one table but can affect any region. For example, discospondylitis is more commonly seen in the lumbosacral area, but can affect any vertebral region.

Table 4.1 Common brain diseases based on the VITAMIN-D acronym for dogs and cats.

Disease mechanism	Specific diseases
Vascular	Canine or feline cerebrovascular disease (ischemic or hemorrhagic)*
Inflammatory/Infectious	Meningoencephalitis of unknown etiology Necrotizing meningoencephalitis Granulomatous meningoencephalitis Infectious meningoencephalitides (bacterial, fungal, rickettsial, viral [distemper])
Trauma	Craniocerebral trauma (head trauma, injury) Traumatic vestibular disease (peripheral)
Toxic	Lead poisoning Metronidazole toxicity Multiple toxicities cause brain signs (see Chapter 23)
Anomalous	Hydrocephalus Chiari-like malformation and syringomyelia Quadrigeminal (arachnoid) cysts Cerebellar hypoplasia Cerebellar abiotrophy Polymicrogyria
Metabolic	Hepatic encephalopathy Hypoglycemic encephalopathy Uremic encephalopathy Electrolyte-associated encephalopathies
Idiopathic	Idiopathic epilepsy Idiopathic vestibular disease
Neoplastic	Primary brain tumors Secondary (metastatic) brain tumors
Nutritional	Thiamine deficiency
Degenerative	Cognitive dysfunction Lysosomal storage diseases Mitochondrial encephalopathies Organic acidurias

*Bold used to indicate common diseases.

Table 4.2 Common spinal diseases based on the VITAMIN-D acronym for dogs and cats.

Disease mechanism	Specific diseases
Vascular	Fibrocartilaginous embolic myelopathy* Epidural hemorrhage Spinal cord hemorrhage
Inflammatory/Infectious	Discospondylitis (bacterial or fungal) Meningitis (steroid-responsive meningitis-arteritis or bacterial meningitis) Meningomyelitis infectious (bacterial, fungal, rickettsial, viral) or noninfectious (unknown etiology, granulomatous meningoencephalomyelitis) Spinal empyema Vertebral osteomyelitis
Trauma	Spinal trauma (fracture/luxations) Traumatic disc extrusion Traumatic atlantoaxial subluxation
Toxic	None
Anomalous	Atlantoaxial instability Chiari-like malformation and syringomyelia Hemivertebra Arachnoid cysts Multiple cartilaginous exostoses Spinal bifida Spinal dysraphism
Metabolic	None
Idiopathic	Disseminated idiopathic skeletal hyperostosis (DISH)
Neoplastic	Primary or secondary spinal tumors
Nutritional	Pathologic fractures due to metabolic bone disease Hypervitaminosis A (cats)
Degenerative	Intervertebral disc degeneration Degenerative myelopathy Degenerative lumbosacral stenosis Degenerative osteoarthritis of articular facets Extradural synovial cysts
Developmental	Cervical spondylomyelopathy

*Bold used to indicate common diseases.

Once the list of differential diagnoses is prepared for the patient, the most probable causes should be ruled in or ruled out, based on appropriate diagnostic tests. The diagnostic approach exemplifying the diagnostic tests used to confirm common brain and spinal diseases is presented in Fig. 4.1 and 4.2.