Clinical insights: Diagnosis of laminitis.

The research article discusses the diagnosis of equine laminitis, a disease linked to insulin dysregulation (ID) due to underlying endocrine conditions or corticosteroid therapy. Accurate diagnosis rests on two factors: recognition of the disease by the horse’s owner and confirmation by a veterinarian. Recent studies have evaluated the reliability of various tests to detect ID in horses, and the findings have the potential to improve early detection, prevention, and management of equine laminitis.

Overview of the Research

• The paper highlights the challenge of accurately diagnosing laminitis, a disease often associated with insulin dysregulation (ID) caused by equine metabolic syndrome (EMS) and pituitary pars intermedia dysfunction (PPID), or corticosteroid therapy.
• Pollard et al.’s study found that although all laminitis cases suspected by owners were confirmed by veterinarians, 45% of veterinarian-diagnosed cases were not recognized by the owners, underscoring the need for improved owner education.
• Research also emphasizes the importance of identifying ID, which manifests in three forms: basal hyperinsulinaemia, an excessive insulin response to oral carbohydrate, and peripheral insulin resistance. This is crucial as ID is a key feature of EMS and PPID and plays a significant role in the development of laminitis.

Diagnostic Approaches to Insulin Dysregulation

• Insulin dysregulation can be detected through different tests. For example, basal hyperinsulinaemia can be spotted by measuring circulating insulin levels, but dynamic tests are preferred due to their low sensitivity.
• Dynamic tests may identify an excessive insulin response to oral carbohydrate or peripheral insulin resistance, depending on the individual test – these include the Oral Glucose Test (OGT), Oral Sugar Test (OST), euglycaemia hyperinsulinaemic clamp (EHC) among others.

Comparative Studies on Preliminary Testing Methods

• A study by de Laat and Sillence found the OGT to be a reasonably repeatable test and suggested that dietary carbohydrate can be a viable alternative to glucose for testing.
• Knowles et al. determined that for dichotomous interpretation (ID or not ID), similar results were obtained using cut-offs of serum insulin concentration at varying time points whether an animal was fasted or not, indicating that fasting is not essential.
• Jocelyn et al. determined the effect of varying the dose of corn syrup on the insulin and glucose response to the OST. It was found that using a dose of 0.45 mL/kg bwt corn syrup improves the OST’s ability to detect ID.

Comparison of OGT and OST

• Smith et al.’s study compared the OGT and OST in horses and found that while they broadly agreed, the results were not always comparable. They recommended ensuring the same test is undertaken each time and advised against using the two tests interchangeably.
• Bertin and de Laat reviewed the various tests currently available to diagnose peripheral insulin resistance, concluding that an ideal test would be able to detect early-stage ID. They noted that factors such as breed, diet, fasting state, or season could potentially confound the results of a specific test.

Consideration of Innate and Environmental Factors

• The research suggests that age, breed, dietary carbohydrate profile and other innate and environmental factors can significantly affect insulin dynamics in equids, highlighting the need to interpret the results of any ID assessment in each individual situation carefully.
• Jacob et al. evaluated the effect of age and dietary carbohydrate profile on insulin and glucose dynamics. The study showed inconsistent influences of these variables on glucose and insulin dynamics, further emphasizing that careful interpretation of the results is essential for proper diagnosis and management of the disease.