Newer tests shed light on causes, treatment of adrenal disorders

Q: Could you update the diagnosis and management of atypical hyperadrenocorticism?

A: Dr. Jack W. Oliver gave an excellent lecture on "Steroid Profiles in the Diagnosis of Canine Adrenal Disorders" at the 2007 American College of Veterinary Internal Medicine Forum in Seattle. Here are some relevant points:

Diagnosis of adrenal disease in dogs, cats and ferrets usually is dependent on the manipulation of the hypothalamo-pituitary-adrenal axis (HPA) and the measurement of cortisol (i.e., ACTH stimulation test; low-dose dexamethasone suppression (LDDS) test; urine cortisol-to-creatinine ratio test; or the combined dexamethasone suppression/ACTH stimulation test).

More recently, other steroid measurements have been used to evaluate the HPA, including steroid hormone profiles and 17-hydroxyprogesterone, which have revealed that suspected adrenal-disease conditions may be caused by steroids other than cortisol (or in addition to cortisol).

Determination of pituitary-dependent hyperadrenocorticism (PDH) or adrenal-dependent hyperadrenocorticism (ADH) usually is made now by evaluation of the four-hour time-point of the LDDS test, by endogenous ACTH measurement or by ultrasound visualization of the adrenal glands.

Hyperadrenocorticism (HAC) is defined as an overproduction of steroid hormones by the adrenal cortex. Cushing's syndrome refers to all causes of hyperadrenocorticism with excess production of cortisol, while atypical Cushing's disease refers to hyperadrenocorticism caused by increased levels of intermediate adrenal steroids that frequently are referred to as "sex steroids."

General steroid hormone profiles

Steroid hormone profiling in veterinary medicine started at the University of Tennessee Clinical Endocrinology Service, on the premise that multiple steroid hormone analyses would increase the diagnostic accuracy of adrenal-function tests.

Measurement of multiple steroids in Pomeranians led to the recognition of a syndrome dermatologists called "Alopecia-X."

Others have reported on adrenal syndromes in dogs called "atypical Cushing's disease" or "adrenal hyperplasia-like syndrome" that used steroid profiling. Cortisol is known to have negative control effect on the HPA axis, but it's now understood that other steroids can have this effect as well.

Steroid profiling in dogs and cats led to the realization that HAC can be due to primary adrenal tumors that secrete other steroids besides cortisol. Steroid profiling in ferrets led to the realization that HAC in this species is primarily due to increased levels of estradiol, 17-hydroxyprogesterone and/or androstenedione in blood, and measurement of these steroids has helped define medical control of ferret adrenal disease.

Steroid profiles have helped us understand the condition of SARDS in dogs, where steroids other than cortisol frequently are involved. Steroid profiling also is aiding the understanding of drug effects on adrenal secretory activity (mitotane, trilostane and melatonin).

Specific steroid hormone profiles

Steroid hormone profiles are indicated when other routine tests of adrenal function are negative (normal findings from ACTH stimulation test; LDDS test; or combined dexamethasone suppression/ACTH stimulation test) and the dog still exhibits signs of Cushing's syndrome, indicating the likely presence of atypical Cushing's disease.

The issue of non-adrenal illness has been raised as a possible consideration in atypical Cushing's disease cases. Results of studies in dogs with chronic illness, but without clinical evidence of HAC, have shown that 17-hydroxyprogesterone (17OHP) concentration may be increased. However, results of other studies of adrenal function testing in dogs with non-adrenal illness have demonstrated only minor effects on test results.

Also, in studies that have measured only 17OHP as a means of detecting HAC, the sensitivity and specificity of using post-ACTH 17OHP concentration as a diagnostic test for HAC were low, and post-ACTH 17OHP analysis was not recommended as a screening test for HAC.

These studies provide evidence that measurement of a singular adrenal intermediate steroid (such as 17OHP) may give equivocal results, but when profiles of steroid intermediates are used, the sensitivity and specificity of the test procedure is much improved. It has been emphasized that adrenal function testing should be performed in dogs with clinical and/or serum chemistry profile evidence of HAC, and not in dogs with non-adrenal-related disease.

Steroids that may be involved with atypical Cushing's disease are androstenedione, estradiol, 17-hydroxyprogesterone, progesterone and aldosterone. Other steroids that are not measured commonly may be involved as well, such as corticosterone and deoxycortisone.

Estradiol is unique because treatment of excess estradiol can be difficult. The hormone can be secreted by tissues other than the gonads or adrenal glands and secretion is independent of ACTH stimulation or dexamethasone suppression testing, as currently done.

For dogs with atypical Cushing's disease (PDH cause), expect the presence of hepatomegaly, hepatopathy and bilateral adrenomegaly, along with increased endogenous ACTH levels and the usual clinical signs, blood-work results and often hair-coat problems.

For dogs with atypical Cushing's disease (ADH cause), expect the presence of hepatomegaly, hepatopathy and unilateral adrenomegaly (and maybe atrophy of contralateral adrenal glands) along with decreased endogenous ACTH level and the usual clinical signs, blood-work results and often hair-coat problems.

For primary hyperaldosteronism conditions, due to primary adrenal tumor or bilateral adrenal hyperplasia, expect hypertension in association with hypernatremia and muscular weakness (cervical ventroflexion, hind-limb weakness) due to hypokalemia. Retinal hemorrhage and blindness and renal disease can occur in cats. For hyperadrenocorticoid cases that also have low aldosterone levels, this pattern can be indicative of a primary adrenal tumor, and ultrasound study is indicated to confirm a tumor's presence or absence.

Treatment implications for primary adrenal tumors

Adrenal steroid profiles reveal that adrenal tumors in dogs, cats and ferrets have a variety of secretory patterns, with serum cortisol levels often being normal. In ferrets, mice, rats, guinea pigs and hamsters, sex steroid-producing adrenocortical tumors occur following gonadectomy, in association with the significant increase in serum gonadotropin levels that develop.

The elevated luteinizing-hormone (LH) level that occurs following gonadectomy leads to neoplastic transformation and expression of LH hormone receptors on sex steroid-producing adrenocortical cells in ferrets and rodents. In spayed female dogs, plasma gonadotropin levels post-gonadectomy rise to levels 10 times what they were pre-gonadectomy, providing evidence of the strong and continuous LH stimulus that possibly plays a role in adrenocortical tumor development.

Surgical removal of adrenal tumors usually is indicated, but age and health considerations impact this decision. If surgery is not an option, then mitotane is usually the next consideration. Adrenal profiles are indicated to determine the functionality of adrenal tumors in light of the multiple hormone secretion patterns that are seen.

• Mitotane. Adrenal hormone profiles reveal that most intermediate hormones are decreased by mitotane the same as for cortisol, but that estradiol may remain unaffected. In cases that continue to have elevated estradiol levels, varying clinical signs of Cushing's disease will be present.

• Trilostane. Enzyme inhibition by trilostane occurs for 3-beta hydroxysteroid dehydrogenase, but also for 11-beta hydroxylase. Thus, 11-deoxycortisol levels build up in dogs treated with trilostane. It is apparent that other intermediate steroid levels increase (androstenedione, 17-hydroxyprogesterone, estradiol and progesterone) in dogs treated with trilostane, which could be due to the 11-beta hydroxylase inhibition, and possibly 21-hydroxylase enzyme inhibition.

The reason only 11-deoxycortisol levels are increased may be due to the length of trilostane exposure (three to seven weeks) as compared to dogs that are exposed to trilostane for extended periods. Trilostane reportedly offers effective control of Cushing's syndrome, but the long-term effects of the elevated intermediate steroids remain ill-defined. Some dogs do have return of clinical signs of Cushing's syndrome while on trilostane. Because trilostane seems to predispose dogs to increased adrenal toxicity with mitotane, an acute switch from trilostane to mitotane treatment should not be done.

• Aromatase enzyme inhibitors (anastrozole, exemestane, melatonin). The aromatase enzyme occurs in gonadal and adrenal tissues (and other tissues such as fat and skin cells), and converts androstenedione to testosterone or estrone, both of which are then converted to estradiol. Neither estrone nor testosterone have been observed to be increased in dogs with adrenal disease, but estradiol frequently is increased and causes many of the clinical signs associated with Cushing's disease. Aromatase enzyme-inhibiting drugs will decrease estradiol levels, but currently are infrequently used in animals due to cost considerations.

• Anti-gonadotropin drugs (melatonin, leuprolide acetate, deslorelin acetate, androgens). Adrenal tissues in different species (e.g., ferrets and rodents) are known to have luteinizing-hormone (LH) receptors present. In ferret studies, anti-gonadotropin drugs are effective in lowering sex-steroid levels. Sex-steroid levels also are decreased in dogs with adrenal disease that are treated with melatonin, but it is not known whether LH receptors are present in canine adrenal tissues. Androgenic drugs have anti-gonadotropin effects via negative feedback effects on the hypothalamo-pituitary tissues.

Results of in vitro cell culture (human H295R adrenocortical carcinoma cells) studies reveal that both 21-hydroxylase and aromatase enzymes were inhibited by melatonin. Also, in dogs with adrenal disease that are treated with melatonin, and repeat adrenal steroid panels are done, cortisol levels are consistently reduced and estradiol levels are variably reduced.

Inhibition of the 21-hydroxylase enzyme would lower cortisol levels, and inhibition of the aromatase enzyme would lower estradiol levels. Estradiol levels are decreased in dogs treated with melatonin. Melatonin treatment for cases of mild adrenal disease in dogs may be effective, and particularly in cases where sex steroids are increased.

Melatonin and phytoestrogens (isoflavones, lignins, genistein) are known to inhibit 3-beta hydroxysteroid dehydrogenase. Lignins and genistein also are known to decrease the activity of aromatase enzyme in MCF-7 cells in vitro. So, combinations of melatonin and phytoestrogens may have efficacy in treating hyperestrinism conditions.

Hyperestrinism in dogs

Hyperestrinism in dogs may be a new and emerging disease entity. In sample submissions to the Clinical Endocrinology Service in 2005 at the University of Tennessee, 40 percent of adrenal panels had elevated estradiol levels (>70 pg/ml). In hyperestrinism cases, estradiol is the estrogen that is increased, ACTH stimulation and LDDS tests are usually normal for cortisol, thyroid function is normal or controlled, liver problems are frequent and typical (very elevated serum alkaline phosphatase, hepatomegaly, steroid hepatopathy, hyperechoic liver by ultrasound study), PU/PD is frequent, panting may be present, hair-coat problems often are present, skin biopsy results suggest an endocrinopathy, there is no change in estradiol level in response to ACTH stimulation or LDDS tests as currently conducted, resistance to mitotane may occur and increase often occurs in response to trilostane.

Effective treatment options for hyperestrinism in dogs is limited, and drugs that could be expected to be efficacious (aromatase inhibitors) often are limiting due to cost. Melatonin and phytoestrogen treatment may be effective for these reasons. Mitotane likely will be effective if the source of estradiol is the adrenal tissues. Trilostane treatment frequently results in increased estradiol levels and this may be a reason why less than effective treatment with the drug sometimes occurs.

Dr. Hoskins is owner of Docu-Tech Services. He is a diplomate of the American College of Veterinary Internal Medicine with specialities in small animal pediatrics. He can be reached at (225) 955-3252, fax: (214) 242-2200 or e-mail: jdhoskins@mindspring.com