Endocrine Diseases Flashcards
What horses are most affected by pituitary pars intermedia dysfunction (PPID)? What 2 complications are associated?
1/5 of horses >15 y/o, with prevalence increasing with each year of age
- laminitis (Founder) - 3rd phalanx, lameness, increased heat and pulsations
- recurrent infections - abscesses
What is the normal anatomy of the equine pituitary gland?
one, layered gland (as apposed to anterior and posterior)
- pars distalis
- pars intermedia
- pars nervosa
What cells are present in the pars distalis and what do they secrete?
- somatotropes: GH
- gonadotropes: LH, FSH
- lactotropes: prolactin
- thyrotropes: TSH
- corticotropes - POMC
What type of cell is present in the pars nervosa and what do they secrete?
magnocellular neurons - oxytocin and ADH
What type of cell is present int he pars intermedia and what do they secrete?
melanotropes - POMC
How does the pituitary produce hormones in healthy patients? How does this change in PPID horses?
periventricular neurons produce dopamine, which inhibits POMC release from melanotropes = minor ACTH, variable endproducts
periventricular cell bodies and nerve endings degenerate, causing a decrease in dopamine and increase in POMC secretion from melanotropes and the pars intermedia becomes enlarged = increased ACTH and byproducts
What is the normal seasonal cycle of ACTH concentration in horses?
tends to remain steady in the beginning of the year, and reaches a peak between mid-July to mid-November
- horses with PPID will have an exacerbated increase in ACTH during this time of the year
What unique clinical sign is seen in horses with PPID?
changes in hair coat = wooly, curly winter coat remains
- generalized/localized hypertrichosis
- abnormal shedding
- hair color changes
What general signs are associated with PPID?
- decreased performance with exercise intolerance
- changed attitude, docile and lethargic
- loss of top line and muscle
- pendulous abdomen, regional fat
- weight loss
- abnormal sweating (increased, inadequate)
What 5 complications are associated with PPID in horses?
- laminitis - increased digital pulses, heat, hoof rings
- desmitis/tendinitis
- suspensory ligament breakdown
- infections - chronic abscesses
- parasitism - increased burden and shedding
What are 4 additional clinical signs associated with PPID in horses?
- loss of reproductive cycle
- blindness
- seizures
- PU/PD
What is the most common way of diagnosing horses with PIPD? What can make this difficult?
history and clinical signs - shedding, coat appearance, attitude, infections, parasites, BCS
- debilitated and aging horses may look like PPID
- concurrent disease affects clinical signs
What 3 laboratory tests are used to diagnose PPID?
- resting ACTH levels*
- TRH stimulation test
- insulin status
(old gold standard = dex suppression test)
What 5 laboratory findings are seen in horses with PPID?
- hyperglycemia
- hyperinsulinemia
- hypertriglyceridemia
- high fecal egg counts (increased shedding)
- relative neutrophilia and lymphopenia
How is it decided which laboratory tests are done to diagnosed PPID? What should be done if tests come back normal?
OBVIOUS SIGNS = resting ACTH level; if normal, perform a TRH stimulation test (11/15-7/15); if that is also norma, retest in 3-6 months
SUBTLE SIGNS = TRH stimulation test (11/15-7/15); if normal, retest in 3-6 months
How is TRH stimulation test performed in horses to diagnosed PPID? What is important to note about this test?
- baseline sample is taken in horses that have not been fed grain for 12 hours
- a follow-up sample is taken 10 minutes after the horse was given 1 mg of TRH IV
- in 4 hours, the samples are centrifuged
- plasma is separated and put in another tube
- plasma sits overnight and the ACTH levels are observed
NOT PERFORMED mid-July to December —> ACTH will naturally be higher and labs do not have a reference interval for this
When is repeat testing recommended when first starting pergolide treatment?
in 30-60 days
