VN June 2023

Vetnews | Junie 2023 15 One of the main hormones that increases is adrenocorticotropic hormone (ACTH). It can cause many problems, including delayed shedding (ranging from a few long hairs to a distinctly long and wavy coat), muscle wasting (especially over the topline), weight loss, increased thirst and urination, either sweating or an abnormally dry coat, behaviour changes, reproductive abnormalities, and frequent infections due to immune system suppression. While symptomatic treatment can address some signs (for example, a long hair coat can be managed by body clipping), the combined problems often lead to debilitation and reduce an older horse’s quality of life. Affected animals struggle with dental disease, chronic sinus and skin infections, intestinal parasites, and general ill thrift. More severe metabolic problems may occur if they develop other disorders (such as colic, diarrhoea, or pneumonia), complicating their treatment. Many horses with PPID also have abnormal glucose (sugar) and fat metabolism, referred to as “insulin dysregulation.” Even though some horses with PPID may appear thin, they often develop abnormal fat deposits over the neck crest, tail head, shoulders, and around the mammary glands or prepuce. Insulin dysregulation places horses with PPID at a higher risk of developing laminitis, which can be the most devastating complication of PPID. Laminitis (founder) is a crippling disease caused by weakening the tissues (laminae) anchoring the hoof wall to the underlying bone. The bone may rotate inside the hoof capsule, leading to chronic lameness, sometimes severe enough to warrant euthanasia. Horses with endocrine diseases can experience mild laminitis episodes that are not easily recognized, especially if the horses are not exercised regularly. Repeated mild laminitis episodes cause cumulative damage over time, leading to more severe lameness. Many horses with PPID already have signs of chronic laminitis at the initial diagnosis. It makes early diagnosis and screening for PPID important to health care for horses in their teens and beyond. HOW IS PPID DIAGNOSED? Horses with advanced PPID can have a classic appearance of a teddy bear with a long and curly hair coat, while animals with mild disease may look normal. However, laminitis may be slowly developing in animals with mild PPID. Screening tests help identify horses with early PPID before their health declines or laminitis develops. Screening is often done by measuring ACTH, frequently elevated in animals with more advanced PPID. For horses with more subtle clinical signs, sometimes called“early”PPID, ACTH can remain normal and dynamic tests may be needed to uncover abnormal hormonal responses caused by PPID. These tests include the overnight dexamethasone suppression test and the thyrotropin-releasing hormone stimulation test, which evaluate the pituitary gland’s ability to respond to the administration of these agents. Unfortunately, diagnostic tests have limitations and may yield normal results in the early stages of PPID. Until more sensitive tests are developed, the decision to begin treatment is sometimes based on the presence of clinical signs alone. Article >>> 16