Pituitary Pars Intermedia Dysfunction and Thyroid disease Flashcards
Describe the pathogenesis of PPID
- Loss of dopaminergic inhibition causes excess pars intermedia hormones b-endorphin, CLIP, a-MSH, and ACTH
- Hyperplasia or adenomatous change to pars intermedia
- Rare extension of the tumour to the brainstem - blindness has been reported, seizures have only anecdotally been reported
Which horses are most commonly affected by PPID?
- Usually 15 years or older, rarely less than 10 years of age = Age related neurodegenerative disorder
- No sex predilection
- Ponies are more likely to be diagnosed (vs affected) than horses: hypertrichosis more apparent, laminitis risk greater
Describe the clinical signs of PPID
- Hypertrichosis (Hirsutism) varies from delayed/abnormal shedding to thick curly coat
- Laminitis
- Weight loss and weight redistribution
- Wasted epaxial muscles and pot belly
- Bulging supraorbital fat pads
- Lethargy/reduced exercise tolerance
- Sweating
- PU/PD
- Susceptibility to infections
Why do we need to use specific tests to confirm a diagnosis of Equine PPID?
- Treatment cost: lifelong treatment is expensive so need to be sure
- Prognosis
- Monitor response to therapy
- Determine insulin dysregulation = laminitis risk!!!
What % of laminitis cases have an underlying endocrinopathy?
90
Describe the tier 1 diagnostic test for PPID
Basal ACTH
- Collect when horse is unstressed (NOT following transport), EDTA tube
- Separate and chill plasma within 3 hours in plastic tube
- Sensitivity and specificity > 80% most of the year, > 99% in Autumn
Describe the tier 2 diagnostic test for PPID
- ACTH response to TRH stimulation
- TRH is rarely, if ever, necessary
- Marginal increased sensitivity and specificity but TRH is unable to be used first line due to the cascade in the UK
How are the results of testing for PPID interpreted?
Results cannot be interpreted without clinical signs and the age of the animal being taken into consideration
i.e. if clear clinical signs and 15 years or older – use more sensitive values to confirm disease – ie rule in unless below lowest values.
PPID diagnosis is not an emergency – if you are unsure test again in a few months
How are positive, negative and inconclusive basal ACTH results interpreted for PPID?
- Positive test (seasonal ref ranges) – begin treatment
- Negative test – no treatment
- If inconclusive (e.g. Clinical signs present)
repeat Tier 1 test (e.g. ACTH in Autumn)
or perform a Tier 2 test (TRH stimulation test measuring ACTH)
How is PPID treated?
- All owners should be informed and given the option of treatment
- Medical therapy does improve quality of life
- Many veterinarians and owners will wait till clinical laminitis develops: Risk of euthanasia when the first episode occurs
Which drug is used to treat PPID?
Pergolide
How is PPID treatment monitored?
Obtain baseline endocrine values e.g. basal ACTH, basal insulin and glucose
Document clinical examination findings
- Appetite, hair coat, water intake / bed wetting
- Body condition score/muscle loss
- Laminitis / lameness
- General demeanour
Why is basal insulin monitored in PPID patients?
Laminitis is usually reason for euthanasia
Insulin is good prognostic indicator - PPID affected horses with high insulin (> 188 µIU/ml) were more likely to develop laminitis and not survive 2 years (vs. < 62 µIU/ml)
High doses of PPID drugs can cause which problem?
Inappetence
How is continued laminitis/high insulin managed in horses with PPID?
- Consider careful dietary control by restricting non- structural carbohydrate access (e.g. cereals, grass)
- Do not severely restrict PPID horses due to risk of exacerbating catabolism
- Increased exercise if possible (depending on laminitis)
- Metformin therapy (if concurrent EMS)
