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

Abstract

Equine Cushing's syndrome, a relatively common and complex condition, is difficult to treat with conventional medicine. Cushing's syndrome involves a hyperplasia or adenoma of the anterior pituitary gland. Biochemical alterations include increased endogenous cortisol, insulin resistance, elevated adrenocorticotrophic hormone, and decreased thyroid hormone levels. Symptoms include hirsutism with no loss of the winter coat in summer, refractory laminitis, weight problems (over- or underweight), polyuria/polydipsia (Pu/Pd), frequent infections, lowered immunity to intestinal parasites, decreased intestinal wall integrity, and infertility.

Laminitis (an inflammation of the laminae of the foot) is a common and often fatal complication of Cushing's syndrome that tends to be refractory to conventional treatment. One of the most common therapies is phenylbutazone, a non-steroidal anti-inflammatory drug (NSAID) known to cause significant changes in the permeability of the intestinal wall. Recent research has shown an intestinal bacterial exotoxin to be one of the triggering factors in laminitis. By removing phenylbutazone and healing the intestinal wall, laminitis becomes more responsive to treatment.

Good hoof-care combined with nutritional management and the application of other modalities, including acupuncture and Chinese and Western herbs, can complete the healing process. The successful treatment of equine Cushing's syndrome is one of the best examples of treating a disease using the holistic approach. While each case requires different combinations of modalities, the outcome is usually positive with individually selected treatments.

(Altern Med Rev 2001;6 (Suppl):S4-S16)

Introduction

Cushing's syndrome is a frequent diagnosis in horses. It has been prevalent in the horse population for many years, but has generally gone unrecognized, partly due to unreliable diagnostic tests. Symptoms of Cushing's -- including unexplained cases of laminitis occurring in the winter or early spring, or hirsutism in older horses -- will often have been present for many years. It is the belief of the authors, however, as well as others, that incidence of the syndrome is increasing and the condition is being seen in younger horses.

Laminitis is one of the more frustrating complications of Cushing's syndrome to treat in equine practice. Chronic cases can take a significant amount of time and energy, yet nonetheless yield unsatisfactory results. Natural medicine provides another avenue of treatment to assist practitioners in dealing with both acute and chronic cases. One of the major factors in healing the laminitic horse is to support intestinal health and repair the basement membrane of the intestinal tract. Pollitt's landmark work has shown that a bacterial exotoxin -- Streptococcus bovis -- has the capability to cause lamellar separation at the basement membrane of laminae of the foot. This bacteria is present in the horse's hindgut and could be released through the basement membrane. Assuming the basement membrane of the intestinal tract can be strengthened through the use of natural medicine, then less exotoxin should be absorbed from the intestinal tract.

The goal in natural treatment of Cushing's and Cushing's-based laminitis is to provide nutritional support to prevent and reverse damage from circulating free radicals, prevent further damage, encourage healthy laminar attachments, and return the horse's metabolism to its proper balance. When managed correctly, with patience and attention to detail, most chronic cases can return to reasonable work. The authors believe that even the most unresponsive cases can often be managed and kept relatively comfortable without the use of drugs.

When treating laminitis with natural medicine, it is essential that each case be approached individually. Furthermore, using multiple supplements or treatment modalities without careful evaluation can be detrimental. Refractory cases may require multiple therapies; however, these therapies should not be used contemporaneously.

Pathophysiology of Cushing's Syndrome

It has been thought that the aging horse normally gets pituitary adenomas of the pars intermedia. (2,3) However, there are conflicting reports in the literature as to the prevalence of the true adenoma. Some sources believe hyperplasia of the pars intermedia occurs more frequently than an actual adenoma. (4,5) Although adenomas and hyperplasia result in similar sets of symptoms, the hyperplasia, being a functional disturbance rather than a tumor, may be easier to treat.

The pars intermedia contains melanotropes, cells that normally use dopamine to process beta-endorphin hormones. (3) In the horse with Cushing's, dopamine is not present, so the melanotropes also produce a small amount of corticotrophin which stimulates glucocorticoid production by the adrenal cortex. The normal negative feedback to decrease corticotropin production does not work since melanotropes in the pars intermedia do not have glucocorticoid receptors. (6) Therefore, corticotropin release continues endlessly. The pars distalis, which does have glucocorticoid receptors, decreases its production of corticotropin. Normally the hypothalamus coordinates the activity of the pituitary gland through the secretion of peptides and amines. (7,8)