Chapter 10 - Endocrine/Nutritional/Miscellaneous Flashcards
Equine Cushing’s disease is caused by an adenoma or hypertrophy of what?
Pars intermedia of the pituitary gland
Horses with PPID have increased levels of which cytokine?
IL-8
Which neurotransmitter is decreased in the pars intermedia in horses with PPID?
Dopamine
What common prescursor protein is cleaved to ACTH, beta-lipotropin and alpha-lipotropin in the pars distalis?
Proopiomelanocortin (POMC)
What main proteins is proopiomelanocortin (POMC) cleaved into in the pars intermedia?
alpha-melanocyte stimulating hormone (alpha-MSH)
beta-melanocyte stimulating hormone (beta-MSH)
Corticotropin-like intermediate lobe peptide (CL1P)
beta-endorphin (beta-END)
Has classical hyperadrenocorticism due to exogenous steroids (iatrogenic) been reported in horses?
No
What is the most classic and consistent clinical sign of PPID in horses?
Hypertrichosis
Hypertrichosis and/or other hair coat abnormalities, laminitis and epaxial muscle wastage or muscle atrophy are the most common signs
Which areas are not typically affected by hypertrichosis in horses with PPID?
Mane and tail
Which drugs are reportedly used for medical management of PPID in horses?
Pergolide (dopamine agonist)
Cyproheptadine (serotonin antagonist)
Trilostane (3b-hydroxysteroid dehydrogenase inhibitor)
Which treatment for PPID in horses has little effect on hypertrichosis?
Trilostane
What husbandry changes can be used to treat PPID in some horses?
Avoiding soluble carbohyrates (e.g. grains, treats) and lush pasture
Routine clipping
Hoof and dental care
Prompt and aggressive treatment of infections
Which mineral is needed for the enzymatic conversion of tyrosine to melanin?
Copper
What are the clinical signs of copper deficiency in horses?
Hair coat fading or leukotrichia around the eyes
What are the cutaneous and systemic signs of vitamin A deficiency in the horse?
Cutaneous:
Rough dull coat, alopecia, scaling, hyperkeratosis, coronitis (dry, scale, cracked hooves)
Systemic:
Night blindness, excessive lacrimation, reproductive problems, neurological disorders
Vitamin A is rapidly destroyed by exposure to which elements?
Oxygen
Light
What is unusual about the spring shed of curly coated horses?
It can be excessive leading to extensive alopecia; mane and tail hair can also be shed
Why and when does alopecia occur in anagen defluxion?
Something (e.g. infection, stress) interferes with the hair cycle resulting in abnormalities of the hair follicle and shaft. The hair shaft breaks leading to loss as the growth phase continues. Loss is acute, within days of the insult.
Why and when does alopecia occur in telogen defluxion?
Something (e.g. stress, pregnancy) causes abrupt, premature cessation of anagen and subsequent synchronisation into catagen then telogen. Hair loss occurs in 1-3 months when a new wave of anagen begins.
What histopathological changes can be seen in anagen defluxion?
Apoptosis and fragmented cell nuclei in the keratinocytes of the hair matrix of anagen hair follicles and eosinophilic dysplastic hair shafts within the pilar canal
What would you see on a trichogram with trichorrhexis nodosa?
Focal areas of swelling along the hair shaft leading to breakage. The ends of broken hairs have longitudinal splits.
What time of year does hair loss occur with seasonal hair loss in horses?
Spring/early summer
In the paper by Thane et al. (2022), did timing of post TRH blood sampling effect the result of TRH stimulation testing for PPID?
Yes, 75% of horses had a >10% difference in values at tests taken at 9 or 11 minutes compared to 10 mins. This would have altered interpretation in 21%
What are the non-cutaneous signs of PPID?
Laminitis, poor wound healing, endoparasitism, chronic infections, pendulous abdomen, PU/PD, abnormal sweating and behavioural change.
How common is PPID in horses 15 years or older?
~ 20%
Baseline ACTH concentration is considered as an excellent test to diagnose PPID with an overall test accuracy above 90%; what is the sensitivity and specificity?
75% and 75%
Which factors cause fluctuation in baseline ACTH concentrations?
Seasonal changes, stress, exercise and disease status
Which factors influence the ACTH concentration following TRH stim testing?
See higher plasma ACTH concentrations in autumn and after starch-rich diets
What is the major risk factor for developing PPID?
15 years of age or older
What causes PPID?
An age-related degenerative disease of dopaminergic neurones affecting the pars intermedia of the pituitary gland.
This leads to over-production of pro-opiomelanocortin (POMC)-derived peptides such as alpha-melanocyte stimulating hormone (a-MSH), b-endorphin, corticotrophin-like intermediate peptide (CLIP), and adrenocorticotrophic hormone(ACTH).
Which enzymes on a liver panel are elevated with hepatocellular injury?
GLDH, SDH, AST
Which enzymes on a liver panel are associated with biliary disease?
Bile acids, ALP, gammaGT
High elevations in fibrinogen are associated with what type of infection?
Bacterial
Which conditions are risk factors for laminitis with steroid use?
Equine metabolic syndrome (obesity and high insulin levels) PPID Previous history of laminitis Ponies Older age
What are differentials for pastern dermatitis affecting the coronary band?
Bacterial infection Coronary band dystrophy (dry) PF (crusting) PV (erosive) MEEDS (crusting/erosive) Hepatocutaneous syndrome (crusting/erosive) Selenosis (dry) Generalised sarcoidosis (crusting/erosive)
What are differentials for scaling and alopecia of the pastern?
Dermatophytosis
Bacterial folliculitis
Vasculitis (looks like this on pigmented skin!)
Localised sarcoidosis (better prognosis than generalised form)
Which diagnostic test should be performed in young horses or those with early signs of PPID (regional hypertrichosis, decreased performance)?
TRH Stimulation Test - if results are equivocal, retest in 3-6 months
Which diagnostic test should be performed in older horses or those with advanced signs of PPID (generalised hypertrichosis, topline muscle atrophy)?
Baseline ACTH - if results are equivocal, then TRH
Stimulation Test
When should TRH testing not be performed?
July-Dec as false positives are more common
Apart from baseline ACTH and TRH sim testing, which other tests can be supportive of a diagnosis of PPID?
- Overnight dexamethasone suppression test
- Magnetic resonance imaging (MRI) specific for pars intermedia enlargement
The chromophil cells of the adenohypophysis (anterior pituitary) produce which hormones?
Acidophils = somatotropin (GH), prolactin Basophils = FSH, LH, TSH
The chromophobes of the adenohypophysis (anterior pituitary) produce which hormones?
MSH
POMC
