Veterinary Medicine - February 2009 - (Page 68) ClinQuiz CAS E 3 12 CAS E 4 LDDS Test Results 12 LDDS Test Results Cortisol Concentration (µ/dl) 10 8 6 4 2 0 0 4 Cortisol Concentration (µ/dl) 10 8 6 4 2 0 0 4 Hours 8 Hours 8 Which statement applies to these LDDS test results (more than one answer may apply)? Which statement applies to these LDDS test results (more than one answer may apply)? The dog has hyperadrenocorticism. The dog has hyperadrenocorticism secondary to an adrenal tumor (ADH). The dog has PDH. PDH and ADH cannot be differentiated based on these results. None of the above The dog has hyperadrenocorticism. The dog has hyperadrenocorticism secondary to an adrenal tumor (ADH). The dog has PDH. PDH and ADH cannot be differentiated based on these results. None of the above A NS W ERS Case 1 A–Correct. The cortisol concentration is > 2 µg/dl eight hours after dexamethasone administration, which is diagnostic for hyperadrenocorticism. B–Incorrect. Although this dog has abnormally high cortisol concentrations at all time points, ADH cannot be definitively diagnosed based on these results. Dogs with adrenal tumors never exhibit cortisol concentration suppression. Because these dogs’ endogenous ACTH concentrations are already suppressed, administering dexamethasone will not cause additional ACTH suppression and, subsequently, cortisol concentration suppression. Furthermore, up to 30% of dogs with PDH also fail to show suppression during an LDDS test. Dogs with PDH that fail to suppress may have disease in the pars intermedia, which is not responsive to dexa- methasone, or they may have large pituitary tumors (macroadenomas). Thus, these results do not help you distinguish between ADH and PDH, and an endogenous plasma ACTH concentration should be measured. C—Incorrect. The results do not show cortisol concentration suppression of at least 50% at the fouror eight-hour time points. D—Correct. Although the cortisol concentrations are high and hyperadrenocorticism can be diagnosed, these results do not help determine whether ADH or PDH is present. Cortisol concentration suppression did not occur during the test, and dogs with ADH never exhibit cortisol suppression. Furthermore, up to 30% of dogs with PDH do not exhibit cortisol suppression. An endogenous plasma ACTH concentration should be measured next. E—Incorrect. These results indicate that the dog has hyperadrenocorticism, but the type of disease (ADH or PDH) cannot be distinguished, so further testing is needed. Case 2 A—Correct. The cortisol concentration is > 2 µg/dl eight hours after dexamethasone administration, which is diagnostic for hyperadrenocorticism. B—Incorrect. As noted earlier, dogs with adrenal tumors will never exhibit cortisol concentration suppression with an LDDS test. C—Correct. The cortisol concentration is 10 µg/dl at baseline and 4 µg/dl eight hours after dexamethasone administration, thus the dog exhibits at least 50% cortisol suppression at some point during the test, which is diagnostic for PDH. D—Incorrect. The cortisol concen- 68 February 2009 VETERINARY MEDICINE
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