Page 940 - Equine Clinical Medicine, Surgery and Reproduction, 2nd Edition

Endocrine system 915

VetBooks.ir Table 6.8 Protocol for the TRH stimulation test

1 Collect baseline plasma sample for ACTH concentration
2 Administer TRH (1 mg i/v)
3 Collect a plasma sample for ACTH concentration at 10 and/or 30 minutes later
Plasma ACTH concentration will be increased to >110 pg/ml (10 minutes) or >65 pg/ml (30 minutes) in horses with pituitary
pars intermedia dysfunction
4 Absence of valid reference intervals in the autumn limits the use of the test between mid-July and mid-November
(northern hemisphere)

of giving conflicting results as to whether or not improve the results of a dexamethasone suppres-
a horse truly has PPID. The presence of hyper- sion test. As improvements can take several weeks
trichosis, the long curly hair coat of horses with or months to become apparent, it is recommended to
advanced PPID, is unique to the disease, and can be wait for at least 4 weeks of treatment before increas-
considered diagnostic in a horse known not to be of ing the dose of pergolide mesylate.
a curly-coated breed. Other therapeutic options investigated include
cyproheptadine and trilostane. Cyproheptadine
Management is a serotonin antagonist that is thought to act by
Horses with PPID tend to have several associated inhibiting secretion of ACTH. There are reports
comorbidities that should be addressed when man- that cyproheptadine improves clinical signs in
aging the disease. Excess hair should be removed horses with PPID, particularly in those with lami-
as needed by body clipping. In addition to body nitis, although it has no effect on endogenous
temperature control, this helps prevent sweat build ACTH concentrations. Trilostane is a competitive
up and facilitates keeping the coat clean and free inhibitor of 3β-hydroxysteroid dehydrogenase that
of infection. Regular dental and hoof care must be has been studied in a limited number of horses.
provided, an adequate deworming and vaccination Given orally, trilostane can decrease the clini-
schedule should be in place and attention must be cal signs of polyuria and polydipsia and improve
paid to provide an adequate diet. Horses with den- laminitis in some horses. It must be emphasised
tal problems that cannot be resolved (e.g. multiple that medications are not curative, and that clinical
missing teeth, wave mouth, excessively worn teeth) improvement will only occur as long as the medi-
may require a complete pelleted feed that has been cation is given.
softened so that it does not require much chewing.
Complications such as laminitis, respiratory or skin Prognosis
infections, sinusitis or dermatitis should be specifi- The prognosis depends on the severity of clinical
cally investigated and treated. signs and occurrence of complications. Horses with
Pergolide mesylate is the recommended treat- minimal complications and treated early in the dis-
ment for PPID. It is a type-2 dopamine agonist that ease have a better prognosis as do those who have
acts by inhibiting proopiomelanocortin production normal blood insulin concentrations and no lami-
by the pituitary pars intermedia, and is the only drug nitis, provided basic husbandry practices and medi-
labelled for use in horses with PPID. Treatment is cal treatment are followed. Concurrent diseases
usually started at 2 μg/kg (1 mg/horse) once a day and infections should be treated promptly and may
orally with doses potentially increasing to up to indicate that the dose of pergolide mesylate may
14 μg/kg if required; however, at high doses anorexia need to be re-evaluated. The prognosis for horses
has been reported. After 1–3 months of treatment, caught later in the disease, with multiple sites of
pergolide mesylate has been shown to improve clini- infections as well as moderate to severe laminitis,
cal signs, lower plasma ACTH concentration and is guarded to poor.