How hormones play a part in laminitis

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Our understanding of endocrinopathic laminitis has grown substantially in recent years. We know that the majority of laminitis cases are caused by either Pituitary Pars Intermedia Dysfunction (PPID) or equine metabolic syndrome (EMS).

Vet Claire Dixon MRCVS explains how this knowledge can aid the diagnosis and treatment of laminitis.

PPID occurs due to enlargement of the pars intermedia portion of the pituitary gland, and results in increased levels of the hormone ACTH. Clinical signs include weight loss, a longer coat, increased drinking and urination, sweating, lethargy and laminitis.

Diagnosis involves:

  • Blood testing for ACTH levels, either at baseline, or following the administration of a hormone to stimulate the pituitary gland (TRH stimulation test).

  • Treatment with pergolide results in decreased ACTH levels and improvement, or resolution of clinical signs. Each horse will require a different dose, so usual practice is to start treatment at a low dose and gradually increase if blood tests show ACTH levels remain high.

  • EMS involves the presence of obesity (or regional adiposity), peripheral insulin resistance or dysregulation, and an increased risk (or presence) or laminitis.

Diagnosis is based on identifying these three factors and so requires blood testing to demonstrate increased insulin levels, or increased insulin in response to feed/sugar challenge.

Treatment

This centres on achieving weight loss and increasing exercise, as this is the best way to improve insulin sensitivity.

However, in horses and ponies with active laminitis, the requirement for rest rules out exercise. This is when we may reach for medical therapy to assist us, until exercise can resume.

Medications used include metformin (which improves peripheral insulin sensitivity in humans and decreases intestinal absorption of glucose in horses), or levothyrozine (which acts as thyroid hormones do to increase metabolic rate).

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