This article is sponsored content brought to you by Boehringer Ingelheim.
Pituitary pars intermedia dysfunction (PPID) and insulin dysregulation (ID) are common and clinically important endocrine disorders of horses, with laminitis representing the most serious shared consequence.5,9 Accurate diagnosis of both conditions is critical, as although the link between PPID and laminitis is not completely understood, available evidence suggests it is associated with ID. 5,9
Diagnosis of PPID should be based on a combination of signalment, clinical findings and endocrine testing.5 PPID is a neurodegenerative disorder predominantly affecting older horses, with disease considered uncommon in equids younger than 12 years of age.3,6 Clinical signs are often insidious and may be mistaken for normal ageing, contributing to underdiagnosis.2 Hypertrichosis remains the only pathognomonic sign, while other common findings include delayed shedding, epaxial muscle atrophy, abnormal sweating, polyuria/polydipsia, recurrent infections and laminitis.5,20
The basal plasma adrenocorticotropic hormone (ACTH) concentration is the most practical and widely used diagnostic test for PPID in practice.5 Blood should be collected into an EDTA tube, chilled within three hours and separated at the laboratory within 12 hours, as ACTH is unstable and prone to degradation with heat exposure.5 Season, geographic location, breed, stress and pain can influence ACTH concentrations and must be considered when interpreting results.21–24 ACTH concentrations increase physiologically during the autumn, necessitating the use of seasonally adjusted diagnostic thresholds.24 The thyrotropin-releasing hormone (TRH) stimulation test can improve diagnostic sensitivity in early or equivocal cases and is best performed in consultation with referral centres or internal medicine specialists.5
ID is defined as hyperinsulinaemia and/or an exaggerated insulin response to feeding and is the hallmark of equine metabolic syndrome (EMS).4,8 ID may occur independently, particularly in younger horses, or concurrently with PPID.5 Importantly, horses with PPID may have ID even in the absence of obesity, and testing for ID is recommended in all PPID cases, especially where there is a history of laminitis.5
Dynamic testing is preferred for the diagnosis of ID, as resting insulin concentrations may miss up to two-thirds of affected animals.15 The recommended dynamic tests are the oral sugar test (OST) and in-feed oral glucose test (OGT).5 These assess postprandial insulin responses using defined glucose challenges and specific sampling times.16–19 Both tests are practical in ambulatory practice, with selection guided by patient temperament, product availability and owner compliance. Results should account for assay-specific cut-offs, feeding status and stress, which can alter insulin responses.5
An evidence-based approach to diagnosing PPID and ID enables early detection of horses at increased risk of laminitis and supports informed management decisions. Careful sample handling, appropriate test selection and interpretation of results in light of clinical findings are essential to achieving an accurate diagnosis in horses with endocrine disease.5
For further details and references download the Recommendations for the Diagnosis and Management of PPID, ID and EMS on Boehringer Ingelheim’s Animal Health Academy. Access code for new users: myAcademy
