Equine PPID and EMS Flashcards
What does Equine PPID stand for?
Equine Pituitary Pars Intermedia Dysfunction
What causes Equine PPID?
Hyperplasia of the pituitary pars intermedia
What is Equine PPID often confused with?
Cushing’s
note: it is not the same thing
Cushing’s is caused by a tumor of the adrenal gland or an adenoma of the pituitary corticotrophs
What is the physiology of the normal Pituitary pars distalis?
- Hypothalamus releases CRH
- Corticotroph cells produce Pro-opiomelanocortin (POMC)
- POMC is then cleaved to ACTH and Beta-lipotropin
- ACTH stimulates the adrenals to produce Glucocorticoids (from the adrenal cortex zona fasiculata)
- Glucocorticoids then have a NFB on the corticotrophs in the pars distalis to decrease ACTH levels
note: there is a normal circadian rhythm with this- concs highest in the morning, plateau in the day and low at midnight
What are the 3 zones of the Adrenal cortex and what do they do?
- Zona glomerulosa: mineralcorticoids
- Zona fasiculata: glucocorticoids
- Zona reticularis: androgens
What is the physiology of the normal Pituitary pars intermedia?
- In response to CRH, Melanotropes produce POMC, which is cleaved into ACTH and Beta-lipotropin
ACTH –> MSH and CLIP (Melanocyte stimulating hormone and Corticotropin like intermediate lobe peptide)
Beta-lipoprotein –> Beta-endorphin (BEND)
Which neurotransmitter inhibits Melanotropes?
- Dopamine, released from the hypothalamus
What is the pathophysiology of PPID?
- There is a Dopamine deficiency released from the Hypothalamus, causing a lack of inhibition on the Melanotropes
- Without inhibition, the Melanotropes respond by proliferating and releasing excess hormones (ACTH and Beta-lipotropin)
- Which causes an increase in the hormones: MSH, CLIP and BEND
- Also causes the loss of the circadian rhythm
What is the signalment of PPID, what animals is it seen most often in?
- All breeds and types: particularly ponies and Morgan horses
- Mean age of 18 - 23 years
- No gender predilection
What are some of the clinical signs associated with Equine PPID?
- Hirsutism (A long and curly hair coat that fails to shed): up to 80% of cases
- Poor hair coat
- Laminitis: 50% of cases
- PU/PD: up to 76% of cases
- Muscle Wasting + Weight Loss: up to 88%
- but Increased appetite
- Docility + Decreased response to pain: due to increased levels of Beta-endorphins
- Lethargy
- Hyper-hidrosis: excessive sweating
- Narcolepsy
- Blindness
- Recurrent Infections
70% of horses with Equine PPID have what else?
Insulin resistance
Equine PPID predisposes the horse to what problems?
increased glucocorticoids cause the following:
- Delayed wound healing
- Recurring infections
- Suppression of Immune Function
What findings may be seen on blood analysis? (CBC and Biochem)
- Anemia
- Stress leukogram: neutrophilia + lymphopenia
- Hyperglycemia
- Elevated liver enzyme activity
- Elevated cholesterol
- Elevated triglycerides
How can Equine PPID be diagnosed?
- Resting ACTH concentration: gold standard
- Thyrotropin Stimulation test: useful in horses with laminitis, but hard to get hold of TRH, but is safer than Dex supp test
- Dex suppression test: has side effects though (laminitis)
What treatments are available for Equine PPID?
- Medication: Pergolide, Cyproheptadine, Trilostane (questionable use of Trilostane)
- Management: good hoof care, dentistry, deworming, and a diet that is easily digestible and low in soluble CHO’s
What is the gold standard medication for treatment of Equine PPID?
- Pergolide
It is a Dopamine agonist, thus giving the horse the hormone it is deficient in
Start 1mg/day, reassess in 4-6 weeks, if no improvement in signs then increase 0.5mg q 3-4 weeks
What is Cyproheptadine, and its dosing?
- Cyproheptadine
It is a Serotonin antagonist
Only 1/3 of horses improve
Start 0.25mg/kg orally, SID, for 4-8 weeks
- If no improvement, increase to BID for 4 weeks
- Still no improvement, switch to Pergolide
What does EMS stand for?
Equine Metabolic Syndrome
aka Insulin Dysregulation Syndrome
What is EMS caused by?
Equine metabolic syndrome (EMS) is a characteristic collection of clinical signs due to the dysregulation of insulin
What is the difference between Compensated insulin resistance and non-compensated insulin resistance?
Compensated insulin resistance: reduced insulin sensitivity, high insulin produced but normal glucose levels are maintained
(Most commonly seen)
Non-compensated insulin resistance: reduced insulin sensitivity, high or normal insulin produced but glucose is high
(Less commonly seen but more severe)
What is the signalment of horses with EMS?
- Young to middle aged (8 - 18 years old)
- Regional to general fat stores
- Insulin resistance
- Sub-clinical to clinical laminitis
- Ponies > Horses
- More common in Warmbloods, Morgans, Arabians, Saddlebreds and American Quarter Horse
- Lack of exercise
- Diet: abundant lush pasture + high levels of grain
What are the clinical signs associated with EMS?
- Obesity
- Laminities
- Colic: due to deposition of fat in and around of the intestines
- Hyper-lipemia
note: a significant overlap with PPID, therefore it should be tested for
How can EMS be diagnosed?
- Insulin levels: horse is fasted for 6 hours and then sample is taken. Normal = <20uIU/mL
- Oral glucose/ sugar test: fast overnight, then give 0.5/1g/kg powder in morning feed, then take blood 2 hours later. Abnormal = >80 - 90 iU/mL
- Combined Glucose Insulin Test: insert catheter previous day, withhold feed for 6 hours, collect baseline sample, then administer 150mg/kg of 50% dextrose IV with 0.1U/kg Insulin IV
Serum glucose and insulin is measured at 45 and 75 mins
Normal: Glucose should be less than the baseline at 45 mins
Insulin should be <30uU/mL at start and at 100uU/mL at 45 mins
What is the treatment for EMS?
Diet: lose weight via diet restriction, soaking of hay, no concentrates and limit pasture (grazing muzzle)
Exercise: start exercise program if possible, or manage laminitis with a farrier
Medications:
- Levothyroxine sodium: increases metabolism
- Metformin: increases glucose uptake into tissues and inhibits gluconeogenesis
Encourage the Owner: repeat tests and measurements of the horse
