Large Animal Neurology. Joe Mayhew

of polysaccharide storage myopathy in horses. Vet Pathol 2006; 43(3): 257–269.

      38 38 Valberg SJ, Lewis SS, Shivers JL, et al. The equine movement disorder “shivers” is associated with selective cerebellar purkinje cell axonal degeneration. Vet Pathol 2015; 52(6): 1087–1098.

      39 39 Hibbs KC, Jarvis GE and Dyson SJ. Crooked tail carriage in horses: Increased prevalence in lame horses and those with thoracolumbar epaxial muscle tension or sacroiliac joint region pain. Equine Vet Edu 2021; 33(7): 368–375.

3 Ancillary diagnostic aids

      

      Disease

        Routine clinicopathological tests

        Genetic markers

        Cerebrospinal fluid analysis

        Electrodiagnostic testing

        Neuroimaging Plain and contrast radiography Computed tomography Magnetic resonance imaging Thermography Scintigraphy Ultrasonography

        Spinal endoscopy

        Brain biopsy

        References

Routine clinicopathological tests

A routine hemogram can assist in the diagnosis of some infectious and inflammatory diseases, lymphosarcoma and trauma with blood loss. Results of routine blood chemistry tests, many of which can be obtained at animal side by the use of convenient point‐of‐care devices, assist in defining many metabolic diseases affecting the nervous system, particularly liver failure, hyperammonemia, renal failure/uremia, hypocalcemia, hypercalcemia, hypomagnesemia, hypokalemia, hyperkalemia, and hypoglycemia. Special serum enzyme and other assays and organ biopsies may be performed to confirm liver and muscle disease, and routine urinalysis has its place in monitoring pigment excretion in systemic diseases (Figure 3.1). Detecting circulating pyrrolic metabolites of pyrrolizidine alkaloids from plants responsible for huge losses of herbivores from liver disease is possible,¹ and in future more use may well be made of detection of plant toxins in blood samples of patients suspected of suffering other plant poisonings. Assays for toxic chemicals and their effector compounds in body fluids and tissues depend on knowledge of the particular intoxicant, e.g., cholinesterase activity for organophosphate intoxication^2,3 and cantharidin for blister beetle poisoning.⁴

      Only rarely do pituitary tumors result in overt neurologic syndromes such as blindness and collapsing episodes, but those that are functionally excreting tumors can often be detected using current endocrinologic testing procedures.^5,6

      Specific serum antibody titers, particularly when assayed on acute and convalescent sera, are helpful in diagnosing infectious diseases such as equine viral encephalitis, equine infectious anemia, equine herpesvirus‐1 myeloencephalopathy, louping ill, malignant catarrhal fever, pseudorabies, and bovine leukemia virus infection. Blood and tissue toxin and nutrient concentrations can assist in diagnosing intoxications and nutritional disorders.

Genetic markers

With accurate phenotypic identification, screening with genetic markers is now available to make the precise identification of several neural and muscular diseases in large animals possible (see text box). These include hyperkalemic periodic paralysis and glycogen branching enzyme deficiency in horses, citrullinemia and complex vertebral malformation in cattle, and scrapie susceptibility in sheep and goats. New genetic markers are certainly becoming available all the time. Testing for many of the genetic markers for neuromuscular disorders in large animals is offered by Veterinary Genetics Laboratory, University of California, Davis, CA, USA ; although there are numerous commercial laboratories offering such tests. A selection is presented in the adjacent text box.

Figure 3.1 In the appropriate clinical setting, red to brown discoloration to urine normally indicates the presence of globin pigments that is positive for same on a dip stick assay and is an excellent ancillary aid to diagnosis. Myoglobinuria is seen in these urine samples from a horse recovering from acute rhabdomyolysis. The acute sample taken is on the left through to the sample taken after recovery on the right. Although myoglobin is usually brown and hemoglobinuria is usually red, as seen here there can be poor distinction based on color alone.

      Selection of neuromuscular genetic tests that are available

Alpha‐Mannosidosis	Dwarfism/Chondrodysplasia	Myotonia in New Forest Ponies
Arthrogryposis Multiplex	Friesian Dwarfism/Hydrocephalus	Neuropathic Hydrocephalus
Beta‐Mannosidosis	Glycogen Branching Enzyme Deficiency	Occipitoatlantoaxial Malformation
Bovine Pseudomyotonia	Hyperkalemia Periodic Paralysis	Progressive Ataxia of Charolais Cattle
Cerebellar Abiotrophy	Idiopathic Epilepsy of Hereford Cattle	Spider Lamb Syndrome
Ceroid Lipofuscinosis	Lavender Foal Syndrome	Stationary Night Blindness
Citrullinemia	Malignant Hyperthermia
Complex Vertebral Malformation	Myosin Heavy Chain‐1 Disorders

      Selection of Large Animal