IN-DEPTH: ENDOCRINOLOGY IN GERIATRICS


PPID is a hormonal imbalance that causes muscle wasting and loss of body condition if untreated. Horses and ponies with obesity or regional adiposity (with or without laminitis) as the only clinical signs are much more likely to have EMS than PPID. Mild muscle atrophy or exercise intolerance is an expected consequence of aging and additional evi- dence should be present to diagnose PPID. There are many causes for infertility, exercise intolerance, and soft tissue injury beyond endocrine disease.


Diagnostic Approach Early in Disease


Early in the disease in horses with less specific clin- ical signs, it may be easier to rule out PPID rather than make a definitive diagnosis due to the poor sensitivity of the diagnostic tests in early cases.10 Start by looking for other causes of the identified clinical problem(s) and correct them. For example, in an older horse with weight loss, perform a de- tailed physical examination and blood analysis to rule out other systemic problems. Correct common causes of weight loss first, such as dentistry, diet, and intestinal parasites. If body weight does not respond once these problems are resolved, then PPID is more likely and testing is indicated. This approach is not dissimilar to how one might ap- proach a high serum creatinine. Before exploring the diagnosis of kidney disease with invasive and expensive tests, the patient will receive fluid to cor- rect prerenal causes of inadequate urine production. If serum creatinine is still high after common causes have been corrected, a more extensive work up of renal health is indicated. Endocrine testing can also be affected by the current state of the horse, such as chronic disease or malnutrition. In the horse with severe weight loss, it is important to recognize that very poor condition can increase ACTH concentrations due to stress of malnutrition (see Figure 2), so diagnostic test results may be misleading if performed before the common causes of weight loss are addressed. PPID is a hormonal imbalance that causes muscle wasting and loss of body condition, not weight gain. In horses and ponies with obesity or regional adipos- ity (with or without laminitis) as the only clinical signs, think EMS. The author strongly recom- mends monitoring all horses with EMS closely as they age as there may be an association between EMS and later development of PPID and animals with both diseases fare worse than those with either disease alone. When testing an obese horse for PPID, it is important to recognize that thrifty ani- mals are more likely to have an increased ACTH concentration before and after TRH administration, especially in the fall, thus limiting the usefulness of the diagnostic tests. PPID is a chronic condition that may underlie development of secondary diseases. Older horses with recurrent bacterial infections should be tested for pituitary dysfunction, as age alone does not cause sufficient changes to the immune system to


Fig. 2. This mare presented with poor body condition, incomplete shedding and a high plasma ACTH concentration (top photo). Af- ter dentistry, anthlemintic treatment and 7 months of improved diet, her body condition improved, plasma ACTH concentration was normal, and she shed completely (bottom photo). At time of death more than a year later, her pituitary gland was found to be normal.


render the horses more susceptible to bacterial in- fections.11 Although there are many causes for re- productive problems in the older horse, if common causes of infertility are ruled out, consider testing for PPID. If an aged horse has no history of inap- propriate sweating in a similar environment, devel- opment of a late-age onset of hyperhidrosis or anhidrosis should cause one to consider PPID. In all of these cases, the indication for endocrine testing is based on a combination of history, sig- nalment, and clinical signs for which other causes have been ruled out. One approach to diagnose early cases is to use the diagnostic tests strategically to maximize their abil-


AAEP PROCEEDINGS  Vol. 64  2018 181


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