Page 942 - Equine Clinical Medicine, Surgery and Reproduction, 2nd Edition

Endocrine system 917

VetBooks.ir from unexplained, chronic, low-grade, recurrent applicable to practitioners have been validated. Two
kinds of tests have been developed, those that inves-
laminitis. Radiographs of the digit during the first
clinically-apparent bout of laminitis often reveals
insulin resistance.
pedal osteitis and other signs of chronic disease. In tigate hyperinsulinaemia and those that investigate
some cases, lean horses can suffer from profound Hyperinsulinaemia: sustained and severe basal
insulin resistance, and therefore obesity should not hyperinsulinaemia is a poorly sensitive indicator of
be considered as a required clinical sign to suspect insulin dysregulation and therefore a dynamic test,
the disease. such as the oral glucose test (Table 6.9) or the oral
sugar test (Table 6.10), is recommended to evaluate
Differential diagnosis the insulin response to an oral carbohydrate chal-
The primary differential diagnosis is PPID. It is lenge. An inappropriate insulin response demon-
important to remember that PPID and EMS can strates post-prandial hyperinsulinaemia and suggests
coexist in the same animal. Although rare in horses, that the horse would be at risk of developing laminitis.
type-2 diabetes mellitus may be suspected in horses Insulin resistance: hyperglycaemia is an indirect
with prolonged unexplained hyperglycaemia, as measure of insulin resistance and is a poorly specific
hyperglycaemia is not a typical trait of EMS. Older and sensitive test. Direct insulin sensitivity testing
reports have associated EMS with hypothyroidism, can be performed with the 2-step insulin response
but horses with EMS usually have normal resting test (Table 6.11).
serum thyroid hormone concentrations and invari- Considering the variability of some of the tests
ably have normal thyroid stimulation tests. Non- and the fact that they do not investigate the same
thyroidal illness syndrome should be suspected in a aspects of insulin dysregulation, combining the oral
horse that presents with the typical clinical appear- glucose/sugar test with the 2-step insulin response
ance of EMS and thyroid hormone concentrations test may improve the detection of horses susceptible
below the reference intervals. to developing laminitis. Other diagnostic tools have
been developed such as morphometric markers with
Diagnosis cresty neck and body condition scores; however, they
Many tests have been described to diagnose insulin can only be considered as indicators warranting fur-
dysregulation in horses but only a few that are readily ther investigation.

Table 6.9 Protocol for the oral glucose test

1 Collect baseline serum sample for insulin concentration after at least 3 hours of fast
2 Administer glucose or dextrose powder (0.75 g/kg p/o) in chaff or by nasogastric tube
3 Collect a serum sample for insulin concentration 120 minutes later
Serum insulin concentration will be increased to <45 mIU/l in normal horses and >85 mIU/ in horses with equine metabolic
syndrome

Table 6.10 Protocol for the oral sugar test

1 Collect baseline serum sample for insulin concentration after at least 3 hours of fast
2 Administer corn syrup (0.15 ml/kg p/o)
3 Collect a serum sample for insulin concentration 60–90 minutes later
Serum insulin concentration will be increased to <45 mIU/l in normal horses and >60 mIU/l in horses with equine metabolic
syndrome