Lecture 13: Neurologic Disease in Ruminants and Peripheral Neuropathies

polio

• thiamine enters during the cycle and creates ATP

• ATP required for molecular pumps in the brain and nervous tissue to move water out of the cell

• no ATP = swelling of nervous tissue

polio clinical signs

• acute onset

• ataxia, tremor

• blindness

• opisthotonos

• convulsions

• recumbency

• ruminations unaffected

• usually no fever

• cranial nerve function is normal

polio neuro exam reveals

central blindness and dorsomedial strabismus

rumen fluid evaluation for polio

• can be sequela to grain overload

• rumen fluid pH can be normal but rumen protozoa were few and the large protozoa were dead

polio diagnostics

• clinical signs, history, and response to thiamine

• several lab tests

evidence of polio but not confirmatory

• RBC transketolase activity should be low

• tissue thiamine concentrations may be normal

• postmortem thiamine concentrations of heart, brain, liver

• blood pyruvate and lactate may be elevated

• CSF may reveal a slight mononuclear pleocytosis and a mild protein elevation with xanthochromia

• evidence of thiaminase

polio necropsy

• provides the most evidence → may reveal a swollen, slightly yellow cerebrum

• autofluorescence of a freshly cut surface of cerebral cortex placed under ultraviolet light is good presumptive evidence

• with acute death, autofluorescence may not always be present

polio risk factors

• plants containing thiaminase

• some drugs like amprolium

• alteration of the rumen microflora

• sulfur

other differentials for polio

• acute lead poisoning

• water deprivation/sodium toxicosis

• histophilus meningoencephalitis

• rabies

• coccidiosis with nervous involvement

• vitamin A deficiency

• pregnancy toxemia

• type D clostridial enterotoxemia

• listeriosis

pathogenesis of polio

• gray matter necrosis from lack of glycolysis with resulting brain edema

• dysfunction of the ATP-dependent Na-K pump leads to cellular swelling

• ATP generation comes from glycolysis

• ruminants depend on ruminal microbial thiamine production

what is the rate limiting enzyme in glycolysis?

transketolase

what is a co-factor for transketolase?

thiamine

polio treatment

• parenteral supplementation of thiamine (vitamin B1)

• 10-20mg/kg initially then maintained with 5-10 mg/kg

• supportive care → correction of rumen environment, fluid support

meningeal worm

• parelaphostrongylus tenius

• aberrant parasite migration through CNS

meningeal worm clinical signs

• head tilt

• incoordination

• difficulty rising

• downers

• progressive weakness in the rear

meningeal worm risk factors

• proximity to water → snails/slugs

• proximity to white tailed deer

• season → late summer, early fall

• multiple species reported → llamas, sheep, goats, cattle, horses, moose

meningeal worm pathophysiology

• MW in WTD lay eggs

• eggs move from CNS to lungs → larvae hatch

• coughed up and consumed → pass in feces

• taken up from the environment by snails and slugs

• snails/slugs eaten by non WTD ruminants, then larvae hatch in GI tract

meningeal worm diagnostics

• signalment and PE → suggestive, often pelvic limb ataxia

• currently the standard is an eosinophilic pleocytosis on CSF tap

• definitive diagnosis is technically larvae in spinal cord

meningeal worm therapy

• antiinflammatories → flunixin, meloxicam

• anthelmentics → fenbendazole

• supportive care → separate, passive range of motion, deep bedding

• may need extensive management or bounce back quickly

meningeal worm prevention

• restricting access to ponds

• a gravel track around fencing

• deer fencing

• guinea fowl → will eat snails and slugs

• camelids can be managed with monthly ivermectin injections

nervous coccidiosis

• may have concurrent enteric coccidiosis

• seizures, snapping of the eyelids

• muscular tremors

• periods of normalcy

• no lesions on necropsy

• sulfonamides, amprolium, and supportive care

• feedlot disease/cold weather

• 70-100% case fatality rate

spinal cord tumors

• uncommon, but primarily lymphosarcoma in older cattle

• common sites → heart, abomasum, spinal cord, retrobulbar area

• sometimes can be diagnosed on CSF tap

hydrocephalus

• thinning brain due to fluid accumulation → vitamin A deficiency

• inherited → hereford, charolais, dexter, holstein, and jersey

hydrancephaly

• congenital absence of brain due to failure to grow or cellular necrosis (more common)

• viral associated (BVD, bluetongue)

peripheral neuropathy of brachial plexus

• injury to the shoulder → trauma, fracture, penetrating wound

• complete flaccidity of the affected limb → absence of sensation, ± ipsilateral horner’s syndrome

peripheral neuropathy of radial nerve

• often damaged from trauma or excessive recumbency

• limb position varies based on where the nerve is injured

• close to elbow → dropped elbow, scuffed toe, distal limb flexion

• distal to elbow → knuckling of carpus, fetlock and pastern, but animal may bear weight

• chronic presentations can have muscle atrophy

peripheral neuropathy of femoral nerve

• traumatic overextension of hip and stifle, or excessive traction during dystocia

• inability to fix and extend the stifle → hoof stays flat on the ground, absent patellar reflex

peripheral neuropathy of sciatic nerve

• largest peripheral nerve

• often damaged with traction from dystocia

• limb hangs behind animal → stifle is dropped and extended, hoof rests on dorsal surface

peripheral neuropathy of peroneal nerve

• branch of the sciatic nerve

• common in recumbent postpartum dairy cattle

• presentation → hyperextension of hock, flexion of fetlock and pastern, dorsal hoof drags on ground, may bear weight if placed in position manually

peripheral neuropathy of tibial nerve

• supports extension to hock and digital flexors common sequelae to dog-bite injuries or injections to caudal leg at level of stifle

• presentation → stringhalt like movement - exaggerated flexion of stifle and carpus

• asymmetric pelvis

• atrophy of gastrocnemius

peripheral neuropathy of obturator nerve

• cattle have shallow acetabulum and small round ligament → predisposes the obturator nerve to injury during dystocia

• clinical signs → hoppy pelvic limb gait, severe pelvic abduction “splay leg”

peripheral neuropathy of facial nerve

• more common in horses

• can be due to trauma, infection, inflammation, masses

• facial muscle atrophy, prolapsed lips, exposure keratitis

• treatment → supportive care, assisted feedings, electroacupuncture

peripheral neuropathy therapy and management

• reduce swelling and inflammation at site of injury

• support and stabilize the denervated area

• maintain the general health of the animal

• NSAIDs

• bandaging, splinting, or casting

• fluid therapy

• range of motion exercises

• float therapy

peripheral neuropathy prevention

• consider the amount of traction used for dystocias → change angle, add more lube, move to C-section

• quick recognition and treatment is key