Research suggests that mild to moderate pain does not interfere with the hormone tests used to diagnose PPID.
A diagnosis of PPID (pituitary pars intermedia dysfunction, also known as Cushing’s Disease) can be supported by assessing the ACTH levels at rest and by measuring the response to a TRH (thyrotropin-releasing hormone) stimulation test.
In PPID, the over-active pituitary gland secretes higher than normal amounts of ACTH and other hormones. But pain itself may also cause increased ACTH levels.
Many horses with PPID eventually develop laminitis. Indeed, many are first suspected of having PPID when they show signs of laminitis.
Does the pain associated with laminitis affect the value of ACTH as a diagnostic test for PPID? Heidrun Gehlen and colleagues at the Equine Clinic, and the Institute of Veterinary Epidemiology, Freie University Berlin, Germany conducted a study to investigate.
Fifteen horses being treated at the Equine Clinic for colic, laminitis or orthopaedic conditions with low to moderate intensity pain were included in the study. Horses were aged less than15 years, with no signs of PPID.
Samples were collected for basal ACTH concentrations, and a TRH-stimulation test was performed.
The intensity of pain was assessed using a composite, multifactorial pain scale. Each horse served as its own control as it was re-tested after the pain had subsided.
The researchers found no significant difference in the ACTH concentration in horses with pain and the controls, between different pain intensities or between disease groups.
They conclude that “measuring the basal ACTH concentration and performing the TRH stimulation test for the diagnosis of PPID seem to be possible in horses with a treated low to moderate pain condition.”
They suggest that “measurement of ACTH and the performance of the TRH stimulation test for PPID diagnostics can, therefore, be performed on horses in pain as long as they are not suffering from massive pain or showing a significantly disturbed general condition.”
For more details, see:
Can Endocrine Dysfunction Be Reliably Tested in Aged Horses That Are Experiencing Pain?
Heidrun Gehlen, Nina Jaburg, Roswitha Merle, and Judith Winter
Animals (Basel). (2020); 10(8): 1426.