PPID diagostic testing

Question 1

What is PPID

Answer 1

• a disease of older/aged horses and ponies which results from a loss of ability to regulate hormonal output from the pars intermedia of the pituitary gland
• as a result hormones from the pars intermedia are secreted excessively
• currently the most appropriate tests are resting ACTH and TRH stimulation

Question 2

What is EMS

Answer 2

• a condition defined by the presence of obesity, insulin resistance and predisposition to laminitis
• when IR develops the cells are less sensitive on action of insulin and result is increased insulin secretion and hyperglycemia
• current tests look at how body can respond to glucose administration

Question 3

what are the melanotrophes in the pars intermedia producing

Answer 3

• POMC
• alpha MSH
• CLIP
• beta endorphins
• beta MSH
• beta LPH
• ACTH

Question 4

what does ACTH do

Answer 4

increase corticosteroids release via adrenal gland stimulation

Question 5

what does MSH do

Answer 5

regulation of appetite, sexual behaviour and melanin production

Question 6

what does CLIP do

Answer 6

modulation of pancreatic exocrine function

Question 7

what do beta endorphins do

Answer 7

behaviour (docility/sedative?)

Question 8

what do beta lipoproteins do

Answer 8

melanin production, steroidogenesis and lipolysis

Question 9

explain the pathology of PPID

Answer 9

• pars intermedia adenoma
• leads to excessive production of POMCs derived peptides
• leads to hyperadrenocorticism

Question 10

describe pathogenesis of PPID

Answer 10

• lack of inhibitory control on pars intermedia cell function that permits development of adenomas
• inhibition is mediated by hypothalamic dopamine
• neurodegeneration of periventricular neurons (oxidative stress) impairs negative feedback to pars intermedia

Question 11

what is the process of taking and interpreting basal plasma ACTH in suspected PPID horses

Answer 11

• single chilled EDTA blood sample is adequate
• seasonal ref ranges published to allow testing at any time of year
• horses with PPID have HIGH plasma ACTH
• 87% sensitivity, 97% specificity

Question 12

describe the process of taking and interpreting TRH stim test in PPID suspected horses

Answer 12

• measures ACTH (not cortisol as in ACTH stim)
• get baseline ACTH
• inject TRH iv
• collect 2nd ACTH 10-30 mins later
• PPID horses have a HIGH baseline ACTH and/or post stimulation plasma ACTH value >100pg/ml
• no seasonal ref ranges so cant perform august-october
• highly sensitive and specific!

Question 13

explain the pathophysiology of EMS

equine metabolic syndrome

Answer 13

• adiposity leads to insulin resistance and laminitis (unknown if obesity develops because or IR or vice versa)
• IR caused by downregulation of insulin signalling by adipokines and accumulation of intracellular lipids
• other factos include inflammation, oxidative stress, altered adipocyte function, altered endothelial function, pro-thrombotic state etc

Question 14

what are the 3 stages of insulin resistance

Answer 14

• compensated IR: normal glucose concentrations maintained by increased insulin output
• uncompensated IR: glucose concentrations increasing and increased insulin concentration
• type 2 DM: end stage, persistent hyperglycaemia because of inadequate insulin output

Question 15

how is EMS diagnosed

Answer 15

aims are to confirm insulin resistance status and rule out PPID
- resting insulin and glucose measurement
- proxies of insulin sensitivity
- dynamic testing (CGIT and in feed glucose challenge)
- blood pressure measurement
- adipokine measurement

Question 16

how does resting glucose and insulin testing help diagnose EMS

Answer 16

• simple and cheap
• high resting insulin strongly suggestive of IR
• low insulin and high glucose = T2 diabetes
• little sensitivity and specificity
• affected by stress, fasting vs fed, season

Question 17

how are PPID and EMS interlinked

Answer 17

• EMS has been shown to predispose horses to develop PPID later in life

Question 18

what are the clinical signs of PPID

Answer 18

• chronic laminities (related to increase insulin and IR)
• PU/PD
• weight loss
• increased docility
• hyperhidrosis
• neurological impariment
• bulgin supraorbital fat pads
• frequent infections
• abnormal oestrus cycle.infertility

Question 19

how can we differentiate PPID and EMS by testing

Answer 19

• signalment and other clinical signs
• ACTH does not increase with EMS

Question 20

are there scenarios where it is difficult to differentiate between EMS and PPID

Answer 20

• stress/pain

Question 21

why is it important to differentiate between EMS and PPID

Answer 21

• management is different
• treatment is different
• EMS can be resolved, PPID is for life