The role of nutritional therapy in the treatment of Equine Cushing's syndrome and laminitis - Equine Cushing's/Laminitis

Alternative Medicine Review, Sept, 2001 by Joyce Harman, Madalyn Ward

Colic, (9) typically low grade and/or recurrent, as well as poor teeth with multiple dental abnormalities, have been reported as clinical signs associated with Cushing's syndrome. (5) The connection between Cushing's and colic and poor teeth is unclear; however, they may be representative of the general breakdown of the system.

The literature also indicates these horses have lowered immunity to intestinal parasites. (5,7) It is the hypothesis of the authors that Cushing's-based laminitis may be associated with poor integrity of the gut wall, since there is evidence of colic and poor immune system function in Cushing's horses.

Chinese Clinical Signs

When studying this disease from the Chinese medical perspective, there are several diagnoses for Cushing's syndrome (Table 2), including kidney (KI) yang deficiency, vacuum heat due to yin deficiency, and qi-yin deficiency. Many of the symptoms fit the classic signs of kidney yang deficiency, such as sore back muscles, weakness, lassitude, increased clear urine, stocking up in the legs, and infertility. (16,17) Chronic illness from other sources can lead to KI yang deficiency. Retention of dampness from spleen deficiency can affect the kidneys by obstructing the movement of fluids. Old age can contribute to KI yang deficiency, which can in turn affect the digestive tract and produce diarrhea. (18)

Infertility occurs frequently in Cushing's, possibly due to a disturbance of gonadotropin secretion in conjunction with the disturbance of the pars intermedia function. (7) Examining the problem from a Chinese perspective, kidney yang deficiency can give rise to infertility problems.

When there is recurrent laminitis concurrent with polyuria and polydipsia the pattern fits a vacuum heat due to yin deficiency. In addition to the laminitis, some of these horses may have respiratory symptoms with either a dry cough or difficult breathing, gastric ulcerations with abdominal discomfort, and a weak, sore lumbar area. (18)

A qi-yin deficiency may manifest with some of the symptoms of yin deficiency listed above, but it may also have digestive symptoms with a loose stool, more fatigue, recurrent upper respiratory infections, and infertility. (18)

Laboratory Diagnosis

Supporting laboratory evaluations can be helpful but also inconclusive in the Cushing's patient. (2,5,8) In equine practice single blood samples are taken whenever the practitioner is at the farm, so there is little standardization of the timing of the samples. Many parameters examined have diurnal variations and may change due to stress or other factors, including the amount of exercise a horse has had before the blood is drawn. Elevated blood cortisol can indicate high stress levels; but is the high cortisol attributable to the Cushing's or has the Cushing's come from chronic stress affecting the feedback system in the pituitary gland? Therefore, cortisol as a single sample is apparently an inaccurate test for Cushing's syndrome. (10,15)

While resting insulin level, (19) ACTH, (10,19,20) and glucose are sometimes utilized, a more useful diagnostic test is the ACTH-stimulation test. (21) A low-dose dexamethasone suppression test (LDDS) is perhaps the most often used; (4,10) however, the authors avoid using LDDS as it further stresses the adrenals. Some horses with Cushing's have insulin-resistant hyperglycemia, which can be identified with a single insulin and glucose sample or an insulin/glucose tolerance test. (6,19,22,23)