Other Causes of Neuro Disease and Peripheral Neuropathies

Lecture 13

List clinical signs associated with polioencephalomalacia (polio).

acute onset of ataxia, tremor, blindness, opisthotonos, convulsions, recumbency

ruminations unaffected

usually no fever

cranial nerve function is normal except for blindness

neuroexam revealed central blindness and dorsomedial strabismus

Why should you do a rumen fluid evaluation in cases of polioencephalomalacia?

polio can be a sequela to grain overload

How can we diagnose polioencephalomalacia?

clinical signs, history, and response to thiamine

lab tests (few readily available)

What can be used as evidence for a polio diagnosis but is not confirmatory?

RBC transketolase activity (should be low)

tissue thiamine concentrations (may be normal)

postmortem thiamine concentrations of heart, brain, and 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

What can be found on necropsy of polio cases?

swollen, slightly yellow cerebrum

cerebellar and/or cerebral herniations may occur in the acute disease

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

List risk factors associated with polio.

plants containing thiaminase —> Bracken fern, Nardoo fern

some drugs such as Amprolium (thiamine analog)

alteration of the rumen microflorae

sulfur —> increased intake or cruciferous plants

What other differentials must be ruled out for polio diagnosis?

acute lead poisoning

water deprivation/sodium toxicosis

Histophilus meningoencephalitis

Rabies

coccidiosis with nervous involvement

vitaminA deficiency

pregnancy toxemia

type D clostridial entertoxemia

Listeriosis

Describe the pathogenesis of polio.

gray matter necrosis from lack of glycolysis (ATP production) with resulting brain edema

dysfunction of the ATP dependent Na/K pump leads to cellular swelling which leads to pressure necrosis of gray matter

ATP generation come from glycolysis —> transketolase is the rate limiting enzyme, thiamine is a co-factor for transketolase

ruminants depend on ruminal microbial thiamine production

How can we treat polio?

parenteral supplementation of thiamine (vitamin B1)

supportive care with correction of the rumen environment (transfaunation, forage feeding), fluid support, ± anti-inflammatories, soft bedding, eye lube

What species is known as the meningeal worm?

Parelaphostrongylus tenuis

List clinical signs of a meningeal worm infection.

head tilt

incoordination

difficuty rising

downers (usually still alert)

progressive weakness in the rear

List risk factors associated with meningeal worm.

proximity to water —> presence of snails/slugs

proximity to white tail deer

season —> late summer/early fall

Describe the pathophysiology of meningeal worms.

meningeal worm in white tail deer lay eggs —> eggs move from CNS to lungs where larvae hatch —> larvae are coughed up and consumed then passed in feces —> larvae are taken up from the environment by small and slugs —> snails and slugs are eaten by ruminants —> larvae hatch in the GI tract then migrate to nervous tissue —> larvae die in nervous tissue of aberrant host —> resulting inflammation leads to clinical signs

How can we diagnose a meningeal worm?

signalment and physical exam are suggestive and often show pelvic limb ataxia

currently the standard is an eosinophilic pleocytosis on CSF tap

definitive diagnosis is technically larvae in spinal cord

How can we treat cases of meningeal worm?

anti-inflammatories —> flunixin, meloxicam, sometimes steroids

anthelmentics —> fenbendazole ± ivermectin

supportive care —> separate from herd, passive range of motion, deep bedding

may need extensive management or bounce back quickly —> can get worse before they get better

How can we prevent infection with meningeal worm?

restricting access to ponds

gravel track around fencing

deer fencing

guinea fowl to eat snails/slugs

camelids can be managed with monthly ivermectin injections for prevention

List clinical signs of nervous coccidiosis.

seizures: opisthotonos, tonic clonic movement, medial strabismus, and snapping of the eyelids

muscle tremors

periods of normalcy

no characteristic lesions on necropsy

How can we treat nervous coccidiosis.

sulfonamides, amprolium, and supportive care, ± anticonvulsants

What are common sites to find lymphosarcoma in cattle?

heart (right atrium)

abomasum

spinal cord (extradural lesions)

retrobulbar area

Spinal cord tumors are generally caused by what neoplasia?

lymphosarcoma

What abnormality results from thinning brain due to fluid accumulation such as in vitamin A deficiency or as a hereditary condition in Hereford, charolais, dexter, holdtein, and jersey cattle?

hydrocephalus

What abnormality is defined as a congenital absence of brain due to failure to grow or cellular necrosis due to viral disease such as BVD or bluetongue?

hydrancephaly

What can cause peripheral neuropathy of the brachial plexus?

injury to the shoulder —> trauma, fracture, penetrating wound

What are signs indicating peripheral neuropathy of the brachial plexus?

complete flaccidity of the affected limbs due to absence of sensation ± ipsilateral horner’s syndrome

What can cause peripheral neuropathy of the radial nerve?

trauma or excessive recumbency during anesthesia or hoof trimming restraint

What are signs indicating peripheral neuropathy of the radial nerve?

limb position varies based on where 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 tricep muscle atrophy

What can cause peripheral neuropathy of the femoral nerve?

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

What are signs indicating peripheral neuropathy of the femoral nerve?

inability to fix and extend the stifle —> hoof usually stays flat on the ground, absent patellar reflex

What can cause peripheral neuropathy of the femoral nerve?

often damaged with traction from dystocia

What are signs indicating peripheral neuropathy of the femoral nerve?

limb hangs behind the animal

stifle is dropped and extended

hoof rests on dorsal surface

chronic injury will lead to profound muscle atrophy

What can cause peripheral neuropathy of the peroneal nerve?

recumbent postpartum dairy cattle

What are signs indicating peripheral neuropathy of the peroneal nerve?

hyperextension of the hock

flexion of fetlock and pastern

dorsal hoof drags on ground

may bear weight if placed in position manually

What can cause peripheral neuropathy of the tibial nerve?

dog bite injuries or injections to the caudal leg at the level of the stifle

What are signs indicating peripheral neuropathy of the tibial nerve?

“stringhalt” like movement —> exaggerated flexion of stifle and tarsus

asymmetric pelvis —> lower side is the affected side

atrophy of gastrocnemius

What can cause peripheral neuropathy of the obturator nerve?

cattle have a shallow acetabulum and small round ligament which predisposes obturator nerve to injury during dystocia

What are signs indicating peripheral neuropathy of the obturator nerve?

hoppy pelvic limb gait

severe pelvic abduction “splay leg”

What can cause peripheral neuropathy of the facial nerve?

trauma, infection, inflammation, masses

What are signs indicating peripheral neuropathy of the facial nerve?

facial muscle atrophy, prolapsed lips, exposure keratitis

How can we treat peripheral neuropathy of the facial nerve?

supportive care

assisted feedings and cleaning out of cheek pouches

electroacupuncture

What are the three key principles for therapy and management of peripheral neuropathy cases?

reduce swelling and inflammation at the site of injury

support and stabilize the denervated area

maintain the general health of the animal