Endocrine and Neurologic disorders

What are some risk factors for hyperinsulinemia-associated laminitis?

• Insulin dysregulation

• Obesity

• Risk factors:

  • age

  • PPID

Hyperinsulinemia-Associated Laminitis

• Lengthening and weakening of the primary and secondary epidermal lamellae

• Primarily mediated by insulin-like growth factor-1 receptor activation

• Insulin dysregulation

• Companion horses and ponies

What are the three types of laminitis?

• Hyperinsulinemia-Associated Laminitis

• Sepsis- associated laminitis

• Supporting limb laminitis

What are some external changes with laminitis?

• Founder rings

• Concave dorsal hoof wall

With laminitis a horse will have bounding pulses on how many limbs?

all 4 limbs

What are some tests or things to look for with laminitis?

• External changes of the hoof

• Radiographs

• Bounding pulses

What are the meds given for hyperinsulinemia?

Sodium-glucose co-transporter 2 inhibitors (SGLT2i)

Pituitary Pars Intermedia Dysfunction

• Equine “cushings” disease - not exactly the same

• Loss of nerves delivering inhibitory dopamine to the pituitary pars intermedia

• Hyperplasia, adenoma formation in PI

• Marked alterations in concentrations of hormones produced by PI

  • ACTH

  • Others

Severe Clinical signs of PPID

• Pathogenic hypertrichosis, failure to shed, change in coat texture/color

• Muscle atrophy

• Hyperinsulinemia - associated laminitis

• Recurrent infections

• Abnormal sweating

• Polyuria/polydipsia

• Exercise intolerance

• Desmitis/tendonitis

PPID treatment options

• Dopamine receptor agonists - replace function of damaged neurons

• Long-term treatment

• Pergolide - Oral, daily

• Cabergoline - Intramuscular, weekly

What are some signs of chronic myopathies?

• Exercise intolerance - stiff stride, reluctance to collect, difficulty in canter

• Muscle fasciculations, stiffness/cramping, pain on palpation

• Muscle atrophy

• Rule out other causes of poor performance

What are some signs of acute myopathy?

• Tachycardia, tachypnea, sweating

• Weakness, recumbency

• Rule out colic, catastrophic injury, neurologic disease, toxicity, acute laminitis

What are some biomarkers with myopathies?

• Creatinine kinase (CK) - serum

  • Muscle enzyme released during myofiber breakdown

  • Peaks 4 hrs post-exercise

  • Normalizes within 48 hrs

  • Exercise test - CK at baseline and 4 hrs after light exercise

• Aspartate aminotransferase (AST) - serum

  • Muscle isoform released during myofiber breakdown

  • Peaks 24 hrs post exercise

  • Normalizes within a week if no ongoing insult

What are some physical things to observe in a neurologic exam?

• Normal cervical range of motion

• Asymmetric muscle atrophy

• Left ear droop, muzzle deviation to right, drooling

• Dull mentation and head pressing at rest

• Abnormal limb placement at rest

Dynamic exam

• Similar to lameness evaluation

• Trying to reveal deficits the horse is hiding - prey animal

• Evaluation from behind and from the side

What are some things you can do on a dynamic exam?

• Walked and trotted in a straight line

• Serpentines

• Backed

• Waked with head elevation

• Circled in large and tight circles

• Walked up and down hills

• Walked over curb

Forebrain disease

altered mentation/behavior/sleep, seizures

Cerebellar disease

intention tremors and generalized loss of coordination/hypermetria, menace deficits, mentation variably affected

Brainstem disease

depend on severity and location, multiple cranial nerves affected, central vestibular disease, mentation variably affected

Peripheral neurologic disease

decreased proprioception

Upper motor neuron →

connection from brain through spinal cord, exaggerated gait/ reflexes muscle tone

Lower motor neuron →

connection from spinal cord to muscles, weakness, decreased gait/reflexes/muscle tone

Eastern/Western/Venezuelan Equine Encephalitis

• EEE is the deadliest to humans and horses

• Transmitted through mosquitos that have fed on infected birds

• Acute onset fever, depression, ataxia, progressing to seizures and death

• Effective vaccine - annual or every 6 months for high risk areas

• Infected horses cannot transmit to humans or other mammals

West Nile Virus

• Depression, fever, coarse muscles tremors, ataxia, death

• Transmitted from infected corvids to mammals

• Effect vaccine - annual

Equine Herpes Virus -1

• Ataxia worse in the hind end, urinary incontinence/urine dribbling, weak tail/anal tone, possible fever

• Not all forms of EHV-1 cause neurologic disease

• Once infected, remain infected for life - stress can cause clinical signs or transmission

• Vaccine does NOT prevent neurologic form of EHV-1 but may reduce frequency of respiratory disease, abortion, or latent infection

Rabies

• Lethargy/stupor/behavior changes, dysphagia, fever, ataxia, urinary incontinence, colic, hypersensitivity, pruritus, convulsion - ALWAYS fatal

• transmissible to humans through saliva, tears, CSF tissues - WEAR GLOVES WITH ALL ACUTELY NEURO ANIMALS ALWAYS

• Effective vaccine - vaccinate annually

• Postmortem immunoassays of the cerebellum and brainstem

Botulism

• Ingestion of pre-formed toxin or clostridial growth in GI tract or wound

• Flaccid paralysis - can be rapidly fatal if diaphragm involved

• Effective but risk-based vaccine

Tetanus

• Clostridial growth in anaerobic wound environments (puncture wound)

• Spastic paralysis, muscles can not relax

• Horses are extremely sensitive to tetanus toxin

• Very effective but relatively short duration vaccine - vaccinate every 6 months and at the time of laceration repair or surgery