Equine Endocrinopathies/Metabolic Disease

Question 1

how is equine polydipsia defined?

Answer 1

> 100ml/kg/day

Question 2

what does PPID stand for?

Answer 2

pituitary pars intermedia dysfunction

equine cushing’s disease

Question 3

which horses are more likely to develop PPID?

Answer 3

common in aged horses

60% of over 20s at post-mortem but not all will have clinical signs

Question 4

which horses should be tested for PPID?

Answer 4

those displaying clinical signs

all horses with laminitis unless young

Question 5

what is the pathophysiology of PPID?

Answer 5

not fully understood

decrease in production of dopamine from hypothalamus, causes decrease in inhibition of pituitary gland

leads to pituitary adenoma –> overproduction of hormones
results in a range of clinical signs

Question 6

what are the clinical signs of PPID?

Answer 6

long curly coat (unknown cause)

laminitis (due to insulin resistance)

PUPD (poss due to decreased secretion of vasopressin)

weight loss

docility

neurological impairment (adenoma)

infertility, skin diseases, periodontal disease

Question 7

why do horses with PPID lose weight?

Answer 7

could be due to:
cortisol production
associated other diseases
parasites - reduced immune function with PPID

Question 8

how is PPID diagnosed?

Answer 8

clinical signs and signalment
gold-standard is post-mortem only
ACTH test and TRH stimulation test

Question 9

why should the reference ranges for PPID testing be adjusted for autumn?

Answer 9

pars intermedia more active in autumn (august to december)

Question 10

what is the first-line test for PPID?

Answer 10

ACTH test - tests resting plasma ACTH concentration

Question 11

how is the ACTH test perfomed?

Answer 11

collect blood - cold, not frozen
plasma is sent off to lab for analysis

reference range adjusted for autumn

Question 12

when is a TRH stimulation test carried out for PPID diagnosis?

Answer 12

if basal ACTH result is borderline

Question 13

how is a TRH stimulation test performed?

Answer 13

take blood sample
inject TRH
blood sample again at 10 mins (+/- 30 mins)

Question 14

how should dose rates for PPID be checked?

Answer 14

re-test in 4-6 weeks

repeat annually as disease progresses

Question 15

what if there is a high clinical suspicion of PPID but a negative test result?

Answer 15

start treatment anyway and assess clinical response

consider routine checking of aged horses regardless

Question 16

how can PPID be managed (non-medically)?

Answer 16

farriery 
clipping 
parasite control 
dental care 
feeding

Question 17

how can PPID be medically managed/treated?

Answer 17

dopamine agonist - pergolide tablets

start with 1mg and monitor/adjust dose
reassess annually

Question 18

what is a common sign that pergolide dose is too high?

Answer 18

may go off food - resolves on lower dose

Question 19

what must you not do with an ACTH sample?

Answer 19

shake about - haemolysis

leave in a warm place

freeze before separating the plasma

send unseparated sample

Question 20

what is the pathophysiology of equine metabolic syndrome (EMS)?

Answer 20

obesity/regional adiposity due to insulin dysregulation/resistance

leads to sublinical/clinical laminitis

Question 21

what are the signs of compensated insulin dysregulation?

Answer 21

high insulin
normal glucose

may have at rest, or only as a response to feeding
could be EMS or PPID (or both)

Question 22

what are the signs of uncompensated insulin dysregulation?

Answer 22

high insulin and high glucose
glucose in urine
type 2 DM

Question 23

what is the direct cause of laminitis in EMS?

Answer 23

hyperinsulinaemia is the direct cause

Question 24

what is the role of genetics in EMS?

Answer 24

genetic predisposition for ID in hardy breeds

ID facilitates breakdown of glucose & fat stores & stimulates hepatic gluconeogenesis

ability to mobilise energy stores and prioritise vital tissues is a survival benefit if poor diet

Question 25

what is the link between IR and obesity in hardy breeds?

Answer 25

strong association IR horses get overweight during summer weight loss in winter associated with poorer diet restores insulin sensitivity by the spring

Question 26

what is the body condition score for obesity in horses?

Answer 26

7/9-9/9

Question 27

what are the body conditions signs of EMS?

Answer 27

cresty neck fat tail head preuputial swelling/mammary gland enlargement

Question 28

what are the differential diagnoses for EMS?

Answer 28

insulin dysregulation can be EMS/PPID or both - can be hard to be sure based on history and signalment test for both

Question 29

can horses be lean and insulin resistant?

Answer 29

yes

Question 30

what is the first-line diagnostic test for EMS?

Answer 30

starve overnight and take blood sample for glucose/insulin bolus glucose/corn syrup blood sample again for insulin and glucose at 2-3 hours usually IR = hyperinsulinaemia and normoglycaemia

Question 31

how can we non-medically manage EMS?

Answer 31

diet - low carb, no concentrate, no grass/grass muzzle exercise - major benefit but difficult if laminitic weight loss - feed 1/3rd less than normal diet, 1.5kg forage per 100kg, soak hay >1 hour, haynet with small holes to make last longer

Question 32

how can EMS be medically managed?

Answer 32

metformin not bioavailable in horses but blocks SI carb absorption - decreases IR only by weight loss

Question 33

what is the pathogenesis of hyperlipaemia?

Answer 33

fatty acid mobilisation triggered by negative energy balance and stress (catecholamine and glucocorticoid release) disease of acute starvation

Question 34

which horses are at an increased risk of hyperlipidaemia?

Answer 34

obesity ponies pregnancy donkeys (more likely to be IR)

Question 35

why are pregnant horses more likely to develop hyperlipaemia?

Answer 35

progesterone in pregnancy causes IR

Question 36

which concurrent conditions worsens lyperlipaemia?

Answer 36

liver failure (hepatic lipidosis)

Question 37

what other conditions can hyperlipaemia lead to?

Answer 37

kidney failure | pancreatitis

Question 38

which hormone impedes development if hyperlipaemia?

Answer 38

insulin IR horses are at risk of hyperlipaemia (EMS, glucocorticoids, catecholamines, progesterone)

Question 39

what are the signs of hyperlipaemia?

Answer 39

depression anorexia ataxia icterus

Question 40

what are the main principles for hyperlipaemia management?

Answer 40

improvement of energy intake and balance treatment of hepatic disease elimination of stress/treatment of concurrent disease inhibition of fat mobilisation from adipose tissue increased triglyceride uptake by peripheral tissues

Question 41

how can hyperlipaemia be medically treated?

Answer 41

glucose infusion (5% at 2ml/kg/hr) partial parenteral nutrition monitor blood glucose (hourly at first) - may need insulin

Question 42

what is the prognosis for hyperlipaemia?

Answer 42

60-100% mortality

Question 43

what is the best prevention for hyperlipaemia?

Answer 43

client education identification of at-risks glucose infusion and insulin if required, to avoid hyperlipaemia