Lecture 7 2/14/25 Flashcards
What are the indications for cushing’s testing?
-compatible clinical signs
-physical exam findings
-supportive clin path
-insulin resistance
-pituitary tumor
-adrenal mass
-systemic hypertension
What is the first step to diagnosing cushing’s?
-rule out exogenous steroids
-discontinue all forms of exogenous steroids if patient is taking them
How long should exogenous steroids be discontinued before cushing’s testing?
-at least 24 hours for any cortisol measure
-4-6 weeks to have the most accurate HPAA function
What are the next steps to diagnosis of cushing’s once exogenous steroids are ruled out/discontinued?
-select an assay
-prep the patient; want them fasted and as low stress as possible
Which screening tests are available for cushing’s?
-UCCR
-ACTH stim
-LDDST
Which differentiating tests are available for cushing’s?
-LDDST
-HDDST
-abdominal ultrasound
-endogenous ACTH
-brain CT/MRI
Which screening test is the most sensitive for cushing’s?
LDDST
What is sensitivity, in terms of a cushing’s test?
-ability to accurately detect all dogs with cushing’s
-few false negatives
What is specificity, in terms of a cushing’s test?
-positive test is definitively diagnostic for cushing’s
-few false positives
What are the characteristics of urine cortisol to creatinine ratio (UCCR)?
-measures urine cortisol pooled
-indicates blood levels over time
-urine conc. normalized is compared to creatinine
-morning samples collected at home
-easy and low cost
-accuracy varies
-sensitive but not specific; good for ruling dz out
How does the value of the UCCR dictate diagnosis/further testing?
-low values are not consistent with cushing’s
-ratios >13 are suggestive of cushing’s but must be confirmed with another test
What is ACTH stim testing the gold standard for?
testing the adrenal reserve/how much cortisol the adrenals can make
What are the steps to a typical ACTH stim test in dogs?
-fast patient
-collect baseline serum sample
-give ACTH cortrosyn TM
-collect a post-cortrosyn serum sample 1 hour later
-do not feed during sampling
What are the characteristics of the ACTH stim test?
-measures adrenal reserve/response to ACTH
-tests positive feedback loop
-can be used to diagnose both Addison’s and Cushing’s
-gold standard for diagnosing iatrogenic cushing’s
-excessive response is diagnostic for cushing’s
-also used to monitor therapeutic response
What are the pros and cons of the ACTH stim test?
pros:
-good sensitivity for PDH
-good specificity
-least affected by illness/stress/meds
-can establish a baseline pre-treatment
cons:
-low sensitivity for ADH
-poor reliability in cats
-expensive in large dogs
What is the basis for the LDDST?
testing the adrenal/pituitary response to negative feedback
What are the steps of the LDDST?
-measure a baseline cortisol
-give dexamethasone IV
-collect serum samples to measure cortisol 4 hours and 8 hours after dex
What is the interpretation of the LDDST?
-normal dogs show suppression of cortisol at 4 and 8 hours
-cushing’s dogs will not suppress at 8 hours
-ADH dogs will have no suppression at 4 or 8 hours
-PDH dogs MAY have suppression at 4 hours, but will not have suppression at 8 hours
What are the data on the LDDST?
-high sensitivity
-moderate specificity
-high positive predictive value
-should be avoided in stressed or sick patients due to risk for false positive result
What are the characteristics of a basal serum cortisol?
-little value in PDH diagnosis
-can be done as a prelim screening
-can be used to monitor therapeutic response
How does the LDDST compare to the ACTH stim in terms of sensitivity and specificity?
-LDDST is more sensitive
-ACTH stim is more specific
What are the characteristics of atypical/occult cushing’s?
-classic clinical signs
-normal HPAA response
-normal adrenal imaging
What are the potential pathophysiologies of atypical/occult cushing’s?
-excess precursor hormones or sex steroids
-early in progression of PDH
-high sustained basal cortisol secretion
-food-dependent
Where is the HPAA feedback broken in different types of cushing’s?
PDH: autonomous release of ACTH despite negative feedback from adrenals/cortisol; ACTH levels are HIGH
ADH: autonomous release of cortisol independent of positive feedback from pituitary/ACTH; ACTH levels are LOW
What is the rationale behind differentiating the type of cushing’s a patient has?
prognosis, treatment options, and treatment response can differ between PDH and ADH
What are the characteristics of the HDDST?
-performed like LDDST
-dexamethasone dose is 10x higher
What is the interpretation of the HDDST?
-suppression occurs in nearly 3/4 of PDH patients at 4 and 8 hours
-suppression does not occur in ADH patients
What are the characteristics of endogenous ACTH?
-single sample
-requires specific handling and storage
-should be measured greater than 8-12 hours post ACTH or dexamethasone
-normal to high values indicate PDH
-values below detection limit indicate ADH
What are the abdominal ultrasound findings in PDH?
-bilateral enlargement
-adrenals of normal size
What are the abdominal ultrasound findings in ADH?
-asymmetrical enlargement
-adrenal mass
-vascular invasion
-calcification
What is a brain MRI used for?
evaluating the pituitary; determining normal pituitary vs microadenoma vs macroadenoma
What is an abdominal CT used for?
evaluating for adrenal mass, invasion, metastasis, and thrombosis
