Today's Veterinary Practice

NOV-DEC 2015

Today's Veterinary Practice provides comprehensive information to keep every small animal practitioner up to date on companion animal medicine and surgery as well as practice building and management.

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tvpjournal.com | November/December 2015 | ToDay's VeTeriNary PracTice caNiNe PiTuiTary DePeNDeNT HyPeraDreNocorTicism series Peer reviewed 43 excessive cortisol interfering with pituitary release of antidiuretic hormone (ADH) or binding of ADH to receptors in the renal tubules. • Abdominal distention and thinning of skin occur due to the catabolic effects of cortisol on tissues, such as muscle and connective tissue. Hepatomegaly due to steroid-induced vacuolar hepatopathy also contributes to the "pot-bellied" appearance of these patients. • Endocrine alopecia mirrors the known distribution of sex hormone receptors in the skin, with endocrine alopecias often sparing the head and extremities. • Panting occurs in both dogs and humans and is believed to result from steroid-induced stimulation of ventilator centers in the brain stem. • Pyoderma and urinary tract infections reflect the immunosuppressive effects of glucocorticoids. • The mechanism(s) behind the steroid induction of calcinosis cutis is poorly understood, though the condition does occur with both iatrogenic and spontaneous hyperadrenocorticism, and can take months to clear following resolution of hyperadrenocorticism or withdrawal of exogenous steroid. Awareness of PDH has increased over time, resulting in the presentation of patients with only mild clinical signs, clinical signs affecting only one organ system (eg, polyuria and polydipsia or alopecia), absent clinical signs, or unusual isolated manifestations of the disease (Table 5). Laboratory Analysis Specifc endocrine tests and imaging modalities are available to diagnose PDH and distinguish between the various causes of hyperadrenocorticism. No single test is perfect and, if the initial screening test is negative and high clinical suspicion of PDH exists, additional tests should be performed to rule it in or out. Endocrine evaluation of patients with PDH and nonadrenal illness can be diffcult; it is important to eliminate or manage the concurrent illness before undertaking adrenal function tests. Further information about diagnosis of canine PDH will be discussed in Part 2 of this series, to be published in the next issue of Today's Veterinary Practice. ACTH = adrenocorticotropic hormone; ACTH-PA = adrenocorticotropic hormone-secreting pituitary adenoma; ADH = antidiuretic hormone; CRH = corticotropin releasing hormone; EGFR = epidermal growth factor receptor; GIP = gastric inhibitory polypeptide; GR = glucocorticoid receptor; LIF = leukemia inhibitory factor; LIFR = leukemia inhibitory factor receptor; MCM7 = minichromosome maintenance-7; PA = pituitary adenoma; Pax7 = paired box protein 7; PDH = pituitary dependent hyperadrenocorticism; POMC = proopiomelanocortin; Sox2 = sex determining region Table 5. Atypical Presentations of PDH in Dogs • Thromboembolic disease • Myotonia • Pancreatitis • Cranial cruciate ligament injury • Facial nerve paralysis • Gall bladder mucocele • Reproductive abnormalities • Hypertension Table 3. Common Clinical Signs of PDH in Dogs • Polyuria and polydipsia • Polyphagia • Abdominal distention • Bilaterally symmetric endocrine alopecia • Panting • Hypertension • Urinary tract infections • Additional dermatologic signs: » Thin skin » Pyoderma » Calcinosis cutis Table 4. Common Laboratory Findings of PDH in Dogs HEMATOLOGIC ABNORMALITIES • "Stress" leukogram: » Neutrophilic leukocytosis » Lymphopenia » Eosinopenia • Mild thrombocytosis • Mild erythrocytosis SERUM BIOCHEMICAL ABNORMALITIES • Increased serum alkaline phosphatase • Milder increase in alanine aminotransferase • Hypercholesterolemia • Hypertriglyceridemia • Hyperglycemia URINALYSIS • Decreased urine specifc gravity < 1.018 • Proteinuria • Urinary tract infection (even in absence of pyuria and bacteriuria)

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