L10b: Pathogenesis and Lab Evaluation of the Adrenal Gland (Glucocorticoids)

Flashcards cover pathogenesis, lab evaluation, and common clinical features of HAC (glucocorticoids) across dogs, cats, and horses, derived from lecture notes.

What is the most common form of HAC in dogs and its usual cause?

Pituitary-dependent HAC (PDH), caused by excess ACTH from a pituitary tumor, accounting for about 80-85% of cases.

what hormone is produced by the hypothalamus in the HPA axis?

Corticotropin-releasing hormone (CRH)

what hormone is produced by the anterior pituitary in the HPA axis?

ACTH

what hormone is produced by the adrenal gland in the HPA axis?

cortisol

MCQ: what describes the change in muscling on this dogs head?

A decrease in size or amount of a cell, tissue, or organ after normal growth has been reached

what are the causes of Cushing’s disease?

1. pituitary tumor

2. adrenal tumor

3. steroid use

what happens to ACTH and cortisol production from a pituitary tumor?

excess ACTH leading to excess cortisol

what happens to ACTH and cortisol in an adrenal tumor?

excess cortisol without ACTH stimulation

what is the most common form of Cushing’s disease in dogs?

pituitary hyperplasia/tumor

pituitary hyperplasia

enlargement of pituitary gland

What is the less common form of HAC in dogs and its typical mechanism?

• Adrenal-dependent HAC (ADH)

• due to adrenal cortisol production from an adrenal tumor or bilateral adrenal hyperplasia

what percentage of dogs with Cushing’s will have pituitary hyperplasia/tumor as the cause?

80%

what percentage of dogs with Cushing’s will have adrenal hyperplasia/tumor as the cause?

15-20%

What is iatrogenic HAC?

HAC caused by long-term high-dose exogenous glucocorticoids leading to Cushing’s symptoms and adrenal atrophy.

how does iatrogenic stress influence hormones of the adrenal gland?

causes negative feedback release of CRH and ACTH

how will adrenal nodular hyperplasia appear?

bilateral enlargement of the adrenal glands

what type of tumors are cortical adenomas and how will they appear?

• benign

• unilateral

contralateral atrophy

atrophy in opposite gland

what organ is often involved in adrenal carcinomas?

kidneys

Name the sequence of hormones in the HPA axis from hypothalamus to adrenal cortex.

CRH → ACTH → cortisol.

What is the role of cortisol in the negative feedback loop?

Cortisol feedback inhibits CRH and ACTH production to regulate the axis.

what pathogenesis should you associate with dogs with HAC?

• primary (adrenal-dependent)

• pituitary dependent

while HAC is less common in cats than dogs, what is it often related to?

insulin resistance from prolonged hyperglycemia

what HAC should be thought of with horses?

PPID caused by pituitary tumor

PPID

pituitary pars intermedia dysfunction

what tests should be done prior to specialized endocrine testing?

baseline chem/ heme/ urinalysis

How does HAC typically affect thyroid hormone levels?

It can cause low T4 and T3 (euthyroid sick syndrome).

What metabolic condition may result from HAC due to insulin antagonism?

Diabetes mellitus

what else can hyperadrenocorticism cause in DM?

insulin resistance and hyperglycemia

Name several co-morbidities commonly seen with HAC in dogs and/or cats.

1. Recurrent UTIs (pyelonephritis)

2. proteinuria (about 50%)

3. hypertension (often >75% in untreated dogs).

what CBC do you expect to see with hyperadrenocorticism?

STRESS LEUKOGRAM

Describe a typical CBC pattern seen in HAC

1. mature neutrophilia

2. LYMPHOPENIA

3. eosinopenia

4. monocytosis

why do you see polycythemia in hyperadrenocorticism?

steroids stimulate bone marrow production of RBC

polycythemia

increased erythropoiesis

why do we see mature neutrophilia in hyperadrenocorticism?

cells cannot get to marginating pool meaning they cannot get to the site of infection

Which liver enzyme is most consistently elevated in dogs with HAC?

Alkaline phosphatase (ALP), elevated in about 95% of cases.

Is hyperglycemia common in HAC, and how often does it occur?

Yes, hyperglycemia occurs in about 51% of HAC cases.

What chemistry findings are associated with HAC?

1. Hyperlipidemia

2. elevated cholesterol and triglycerides

3. lipemia

4. lowered UN

What urinary finding is common in HAC due to PU/PD?

1. Dilute urine with low USG

2. UTIs (49%)

What is the UTIs frequency and presentation in HAC?

UTIs are common (about 49%), often without pyuria due to immunosuppression.

relying on diagnostic tests can lead to…

false positive

many assay testings are affected by…

stress and steroid administration

what does HAC diagnosis require?

1. demonstration of increased cortisol production OR

2. decreased HPAA sensitivity to glucocorticoid feedback

what are the indicators for performing diagnostic tests for HAC?

1. pituitary or adrenal tumor

2. diabetic dog that persistantly has poor response to high doses of insulin

3. persistent hypertension

Why is basal cortisol not reliable for HAC diagnosis?

Cortisol varies with stress and pulsatile ACTH; basal levels can be misleading.

What can basal cortisol help to rule out clinically?

Addison’s disease (adrenal insufficiency) when cortisol is very low.

What are the two main criteria for diagnosing HAC?

1. increased cortisol production

2. decreased HPAA sensitivity to glucocorticoid feedback

How do steroids interfere with cortisol assays?

• cortisol is 100% affected by endogenous cortisol

• prednisolone ~69%

• dexamethasone ~0.1% cross-reactivity.

basal cortisol refers to

 the level of cortisol in the blood under resting or non-stimulated conditions, without any external influences

what does basal cortisol represent?

 the normal baseline production of cortisol by the adrenal gland.

Which synthetic glucocorticoid interferes least with cortisol assays?

Dexamethasone.