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 the resting ACTH level performed in horses to diagnose PPID?
- baseline sample is taken and placed in a EDTA tube
- in 4 hours, the sample is centrifuged
- plasma is separated and put in another EDTA tube
- plasma sits overnight and the ACTH levels are observed
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
What are 2 other potentially supportive tests used for PPID diagnosis?
- overnight dexamethasone suppression
- MRI specific for PPI enlargement
In what ways can horses with PPID be managed to alleviate clinical signs?
- quality nutrition
- keep optimal BCS
- dentistry: float older horses 2x a year
- parasite control
- water supply
- hoof care
What medical treatment is recommended for horses with PPID?
life-long, oral pergolide (Prascend) every day
- dopamine agonist that replaces the deficit of dopamine to decrease melanotrope formation of POMC
What side effects are associated for pergolide (Prascend) treatment of PPID? How is treatment altered when this occurs?
- inappetence
- weight loss
- lethargy
stop treatment until appetite returns and re-introduce pergolide at 1/2 dose BID for 4 days
What are the initial and long-term responses expected with pergolide treatment in horses with PPID?
INITIAL = better attitude, increased activity, resolved PU/PD and hypoerglycemia
LONG-TERM = improved hair coat, muscle mass, and shape, and less likely to develop infections and laminitis
When is repeat testing recommended when first starting pergolide treatment?
in 30-60 days
What is the role of insulin?
produced by the pancreas following increased blood glucose resulting in mediated glucose absorption in the liver, adipose tissue, and muscle
How is insulin production affected by PPID?
INSULIN RESISTANCE!
- decreased tissue response or uptake of insulin
- pancreas secretes more insulin to compensate
- this results in high insulin levels, which deprives tissues of glucose (hoof = laminitis)
