tive control of pars intermedia endocrine function and the overproduction of proopiomelanocortin- derived peptides produced by the pars intermedia melonotropic cells, including adrenocorticotropin (ACTH), alpha-melanocyte-stimulating hormone, beta endorphin, and corticotrophin-like intermedi- ate peptide. This overactive pars intermedia be- comes hyperplastic on histological examination initially and in more advanced disease can become adenomatous12 but is not a primary tumor like own- ers may assume.


Treatment


Medical treatment of PPID involves daily oral ad- ministration of pergolide, a dopamine agonist, which is licensed (FDA approved) for use at a dose from 0.002–0.01 mg/kg PO q 24 h.a Treatment should be initiated at the low end of the dose range (to the nearest 0.5 mg) and gradually increased, if required, based on clinical and endocrinological response.13


Body Weight 200–350 kg


350–600 kg 601–850 kg


Side Effects


Although pergolide has few specific side effects, up to one-third of treated horses will demonstrate tran- sient inappetence on pergolide and around 10% may appear dull or lethargic.8 These side effects, espe- cially inappetence, were more common when per- golide was first used at much higher initial doses.14 Therefore, careful attention to gradual increases of the dose can reduce the occurrence of these side effects. If signs of inappetence or depression are observed, the dose can be reduced by increments of 0.001 mg/kg BW13 or stopped for a short period (2–3 days or until appetite returns) and the dose re- started at half of the original dose.15,16 Interestingly, when pergolide was administered


in target animal safety studies, depression and/or anorexia were not observed in normal horses, even at doses as high as 0.008 mg/kg for 6 months.8 There were decreases in heart rate variably between geldings and mares but only to the normal range.8 Further research using normal horses in a blinded controlled crossover design trial with more detailed heart rate observations using Holter monitor record- ing at rest, during stimulation, and exercise did not demonstrate a difference in heart rate between groups.17 Despite the frequency of side effects, it is impor-


tant to recognize that signs of inappetence and leth- argy are nonspecific and may accompany many diseases. Aged horses, even without PPID, have an increased risk of concurrent disease,4 so on identifi- cation of these clinical signs, especially if they don’t rapidly resolve with a reduction of dose, it may also be pertinent to investigate for concurrent disease.


Starting Daily Dose 0.5 mg


1.0 mg 1.5 mg


IN-DEPTH: ENDOCRINOLOGY IN GERIATRICS Monitoring


Notwithstanding the improvements that most horses can expect from medical treatment, owners need to be aware that treatment is not curative, and medical treatment is a commitment that should be continued indefinitely, with monitoring, dose adjust- ments, and ongoing care as important parts of therapy.13


General Health Monitoring


Most horses with PPID will be in their “teens” or older, with an increasing likelihood of diagnosis ev- ery year after 15 years of age.7 Aged and geriatric horses have an increased susceptibility to a range of conditions and diseases, particularly dental disease (including periodontal disease), lameness, eye con- ditions, heart or lung conditions, and skin conditions (including tumors such as sarcoids and melano- mas).4 PPID may increase the risk of intestinal parasitism18 but does not alter a routine hematolog- ical or biochemical profile.7 Despite an association between alterations in blood tests and PPID being reported,16 it is important to note these have only been found in case series and not field-based epide- miological research.19 Case series rely on horses presented for veterinary care and, hence, suffer from owner bias. As noted in the companion paper on this in-depth session, epidemiological research has shown that many of the clinical signs of PPID are considered normal signs of aging by horse owners, including hypertrichosis and muscle atrophy,20 so owners may inadvertently delay presentation for veterinary care until concurrent disease occurs.19 Therefore, alterations in blood tests and concurrent illnesses should be investigated as concurrent dis- ease, not ignored or presumed only associated with PPID. In the aged population of horses presenting with


PPID, there is a greater possibility of serious dental problems as well as periodontitis and diastema than in younger horses,21 so dental work should be car- ried out with veterinary care, including sedation, pain relief, and anti-inflammatory or other medica- tion as necessary. If owners are fully informed of the high prevalence of these conditions in their horses’ age bracket and engage in regular health checks with appropriate blood testing, then the best outcomes can be achieved.


Monitoring Clinical Signs of PPID


Improvements in clinical signs are important moni- toring tools and attention should be paid to trying to collect these as objectively as possible rather than just relying on endocrine “numbers.” Body condi- tion score (and muscle score), hair coat, demeanor, appetite, Obel grade of lameness if lame (or evidence of subclinical laminitis like laminitic rings, widened white line, or dropped soles if not), and water intake can all be monitored. Baseline values should be obtained in consultation with the owner, then sub-


AAEP PROCEEDINGS  Vol. 64  2018 189


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