Animal Health - Equine Division - page 6-7

PPID DEFINED
Pituitary Pars Intermedia Dysfunction (PPID), also known as Equine Cushing’s Disease, is the most common endocrine disorder in
horses. An estimated 21% of horses and ponies over the age of 15 are affected by PPID, and the prevalence increases for each year
of age.
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Although the pathophysiology differs from humans and dogs with Cushing’s, PPID is now the preferred scientific name as it
specifies the exact area of the pituitary gland affected in the horse.
PPID is a chronic progressive disease. PPID causes multiple health problems for the horse, including laminitis and recurrent
infections. Ponies and Morgans are overrepresented, but all breeds and types of equids may be affected.
2
Horses with a history of
Equine Metabolic Syndrome (EMS) are thought to be at higher risk of developing disease at a younger age.
2
PATHOPHYSIOLOGY
The equine pituitary is divided into three regions: the pars distalis (anterior pituitary), the pars intermedia (intermediate lobe), and
the pars tuberalis (posterior pituitary). Dopaminergic neurons originating from the hypothalamus innervate and inhibit the secretory
activity of the melanotrophs of the pars intermedia. Dopaminergic inhibition to the pars intermedia normally decreases with aging.
However, degeneration of dopaminergic neurons occurs at an accelerated rate in PPID. The exact cause of degeneration is poorly
understood, but is thought to result from chronic oxidative damage.
3
As dopaminergic inhibition decreases, melanotrophs of the
pars intermedia become hyperplastic, increasing secretion of proopiomelanocortin (POMC) peptides such as α-MSH, β-endorphin,
CLIP, and
now
ACTH, which is
not
normally produced in significant amounts from this region. Elevated ACTH from the intermediate
lobe acts on the adrenal glands to stimulate cortisol which, along with multiple other hormones, results in the unique, individual
clinical presentation of PPID. With hyperplasia of the pars intermedia, functional pituitary adenomas develop over time.
CLINICAL SIGNS
Hypertrichosis (previously termed hirsutism) and muscle atrophy are commonly recognized in PPID. However, a variety of non-
specific clinical signs have been associated with early or advanced disease:
New Developments in an Old Problem:
Pituitary Pars Intermedia Dysfunction (PPID)
Early signs of PPIDmay include:
• Regional hypertrichosis; subtle haircoat abnormalities
• Metabolism shift; from an“easy keeper”to lean body condition
• Regional adiposity; cresty neck, tailhead, supraorbital region
• Poor performance; attitude/behavioral changes, dullness, docility
• Reproductive problems; subfertility, pseudolactation
• Laminitis
Advanced signs of PPIDmay include:
• Generalized hypertrichosis; long, curly, dull haircoat that fails to shed despite change in season
• Muscle atrophy with regional adiposity; loss of topline, pot-bellied appearance
• Recurrent infections; white line disease, subsolar abscesses, scratches, periodontal disease, sinusitis
• Inappropriate sweating; hyperhidrosis or anhidrosis
• Polyuria/polydipsia
• Neurologic disorders; blindness, seizure, ataxia
• Laminitis
Signs of PPID may be discounted to the normal aging process, but it is important to recognize that this disease develops very slowly
over time, making early detection difficult. Owners should record when their horse sheds its winter haircoat and compare this time
with herdmates to detect delayed shedding.
2
Regional alterations in length, subtle changes in color, texture, or thickness of hair
may indicate early PPID. Generalized hypertrichosis (persistence of hair follicles in anagen) is easily recognized and considered
pathognomonic for PPID.
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The presence of this retained haircoat is considered advanced disease and efforts at detection of PPID
should begin long before this textbook sign is observed. Chronic, recurrent infections that fail to respond appropriately to treatment
may also occur due to immunosuppression. In some cases, diagnosis of PPID may be
missed
altogether due to focus on treatment
of the obvious infection and lack of other overt signs of PPID. A common client complaint in early and advanced PPID is lameness or
“foot soreness” associated with insidious onset laminitis which progresses to debilitating laminitis over time. Laminitis may be the
only
presenting sign, and may be difficult to recognize unless the horse is examined on a hard surface. Laminitis has been associated
with the presence of hyperinsulinemia and suggests a poorer prognosis for long-term management of PPID.
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by Marian G. Little, DVM, Field Equine Professional Services, Boehringer Ingelheim
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