Texas Equine Veterinary Association

www.texasequineva.com • Page 12 ABSTRACT Endocrinopathic laminitis is a common condition diagnosed in adult horses. The scientific understanding of pituitary pars intermedia dysfunction(PPID) and equine metabolic syndrome (EMS) is increasing quickly due to the large amount of horses presenting with these conditions and the large amount of research being performed to better treat these affected horses. This review focuses the current understanding of the clinical presentation, diagnosis and treatment of PPID and EMS. REVIEW OF CURRENT UNDERSTANDING OF ENDOCRINOPATHIC LAMINITIS 1. INTRODUCTION Endocrinopathic laminitis is defined as laminitis developing from hormonal influences rather than in association with pro-inflammatory and intestinal conditions. 1 Conditions associated with endocrinopathic laminitis fall into two basic categories that can sometimes overlap including pituitary pars intermedia dysfunction (PPID) and insulin dysregulation, including hyperinsulinemia and insulin resistance (IR) which are components of equine metabolic syndrome (EMS). Insulin dysregulation can occur in conjunction with PPID. PPID is also called Equine Cushing's Disease and usually occurs in horses more than 15 years of age and has a prevalence rate of 21% in this age of horses. 2 The disease in horses is caused by hyperplasia or neoplasia of the pars intermedia whereas pituitary dependant hyperadrenocorticism in the dog usually develops in the pars distalis. Corticotrophs of the pars distalis and melanotrophs of the pars intermedia secrete hormones derived from the hormone pro-opiomelanocortin (POMC). While adrenocorticotropin hormone (ACTH), beta endorphin, and beta lipotropin are the primary products of POMC processing in the pars distalis, melanotrophs of the pars intermedia further process ACTH and REVIEW OF C U R R E N T U N D E R S T A N D I N G O F ENDOCRINOPATHIC LAMINITIS release alpha melanocyte stimulating hormone (α MSH) and corticotrophin-like intermediate peptide (CLIP). Mammalian pars intermedia melanotrophs are under toxic inhibition of dopaminergic periventricular neurons and loss of dopaminergic inhibition results in pars intermedia hyperplasia. 3 Abnormal pars intermedia tissue in horses contains markedly reduced amount of dopamine, about 10% that of normal pars intermedia tissue, consistent with a specific loss of hypothalamic dopinergic innervations. Recent evidence suggests that this loss of dopinergic innervation is due to oxidant induced injury to hypothalamic tissue. 4 Typical clinical signs of PPID may include delayed shedding of the winter haircoat, hypertrichosis (commonly referred to as hirsutism), skeletal muscle atrophy, poyluria and polydipsia, immunosuppression, regional fat distribution, abnormal sweating, recurrent infections, abnormal reproductive cycles and infertility, neurological deficits and night blindness, rounded abdomen, as well as laminitis. 5 EMS is both an endocrine and metabolic disorder that can lead to laminitis. Although the reports describing a phenotype that we now recognize as EMS were published as far back as the 1970s, the term EMS was not introduced to the equine medicine vernacular until the early part of the last decade. 6 A number of different names have been use to describe this condition, including obesity-associated laminitis, peripheral Cushing's syndrome, pre- laminitis metabolic syndrome, endocrinopathic laminitis, and pasture-associated laminitis. The American College of Veterinary Internal Medicine (ACVIM) has defined the phenotype of EMS by the following criteria: 1. Generalized obesity and/or increased adiposity in specific locations (regional adiposity): An increase in the amount of fat surrounding the nuchal ligament ("cresty neck") is a common example of regional adiposity in affected animals but abnormal ROBERT JUDD, DVM, DABVP Judd Veterinary Clinic

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