PPID Clinical Syndrome and Diagnosis

Pituitary pars intermedia dysfunction (PPID), also known as equine Cushing’s disease, is the most common endocrinopathy of equids. PPID increases in prevalence with age and may affect 15-20% of equids over 15 years of age and hair coat changes, consistent with PPID, were recently reported in nearly 40% of equids (mostly ponies) over 30 years of age. There is no apparent sex or breed predilection; however, PPID is more common in ponies than horses. Cushing’s disease in horses develops consequent to hyperplasia or adenoma formation in the pars intermedia that appears to be due to loss of dopaminergic hypothalamic innervation. Hyperplastic melanotropes in the pars intermedia produce excessive amounts of pro-opiome-lanocortin (POMC) and a number of POMC-derived peptides including immunoreactive adreno-coticotropin (ACTH) peptides, although the ACTH peptides may not all be bioactive. Clinical syndromes: A variety of clinical signs can be observed in PPID affected equids: lethargy, muscle wasting, localized fat deposition, polyuria and polydipsia,chronic laminitis, recurrent infections, and neurological deficits. However, a pathognomonic sign of PPID is a long and often curly hair coat that fails to shed, reported in more than 80% of cases. Hair coat changes with PPID appear to progress over several years from delayed shedding and persistence of long hairs under the jaw, ventral neck, and palmar and plantar aspects of the distal limbs to a generalized long, shaggy hair coat that fails to shed. Although the term hirsutism has become firmly ingrained in the equine veterinary literature to describe this characteristic hair coat, a more appropriate descriptor is hypertrichosis as the hairs of PPID-affected equids are characterized by persistence in the anagen (growth) phase. Chronic, insidious-onset laminitis is perhaps the major clinical complication of PPID with nearly 50% of horses affected. Although the condition is more amenable to management in ponies due to their lower body weight, chronic or recurrent pain with exacerbation of laminitis or associated foot abscesses is often the reason for euthanasia. More recently, additional musculoskeletal complications of PPID, including tendonitis and suspensory desmitis, have also been suggested to be associated with PPID in mature performance horses. Finally, type 2 diabetes and infertility maybe other clinical syndromes of PPID, affecting equids before hypertrichosis may be recognized. […]