TREES current herd consists of 7 horses with confirmed Cushings, or PPID, diagnoses, and at least 3 other horses than show some symptoms, but had "normal" ACTH levels when tested. Several times, we've discussed with our vet the possibility that the parameters defining "normal" may need to be re-evaluated. If we had several horses showing clinical signs of PPID even when testing as Normal, it is likely that other owners experience the same thing.
Now, from the Jan2, 2009 horse.com article, "Equine Endocrine Disorders Discussed at AAEP," we see:
"It was pointed out that PPID is difficult to detect in its earliest stages, while advanced disease is relatively easy to recognize. The two most commonly used tests for PPID--resting adrenocorticotropin hormone( ACTH) concentrations and the overnight dexamethasone suppression test--can be used to confirm the diagnosis. However, these tests are less likely to yield positive results when PPID is first developing, so clinical judgment must be relied upon in these cases."
So, it's not our imagination. Some horses exhibit clinical symptoms even though the test results do not confirm the diagnosis.
Fortunately,
"New diagnostic tests are being developed for PPID and might allow earlier detection of the disorder. These include the combined dexamethasone suppression/thyrotropin-releasing hormone (TRH) stimulation test, TRH response test (with ACTH concentrations measured 10 and 30 minutes post-injection), and oral domperidone challenge test."
It may seem odd to be so excited about these little advances but, considering that ten years ago Cushings was often viewed as a terminal illness, these "little" things can mean a lot to people caring for long-time equine family members. The sooner a PPID patient is started on treatment and modified management techniques, the better the chances of preventing serious complications, which translates into a better long-term prognosis.
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