Equine pituitary pars intermedia dysfunction: current perspectives on diagnosis and management

Figures & data

Table 1 ACTH upper reference ranges, sensitivity, and specificity data from different locations and seasons

Location/latitude	Subtropics Southern hemisphere (−27° 24′ to −24 ° 54′)^Citation15			Temperate Northern hemispherea,^Citation44,Citation46
	Sn (%)	Sp (%)	Cutoff	Cutoff
ACTH
Autumn	100	95	77.4 pg/mL
Winter–summer	80	82	29.7 pg/mL
Late summer to mid-autumn				47 pg/mL
Late autumn to mid-summer				29 pg/mL
α-MSH
Autumn	100	97	165.4 pmol/L
Winter–summer	59	93	52 pmol/L
Late summer to mid-autumn				No precise value documented
Late autumn to mid-summer				35 pmol/L

Note:

a Northern hemisphere reference ranges have been calculated on normal distributions and 95% confidence intervals, with no sensitivity or specificity data to date.

Abbreviations: ACTH, adrenocorticotropin hormone; cutoff, upper limit of normal reference range; α-MSH, α-melanocyte-stimulating hormone; Sn, sensitivity; Sp, specificity.

Table 2 PPID test protocols

Test	Protocol	Sample type required
ACTH	• Blood collected in plastic EDTA vacutainer	Plasma (EDTA)
	If ≤48 hours to laboratory processing
	• No further processing required
	If ≥48 hours until laboratory processing
	• Centrifuge sample
	• Separate plasma and place in a plain (red top) plastic vacutainer, marked EDTA Plasma
	• Freeze plasma and send on ice to laboratory
TRH stimulation test measuring ACTH	• Collect blood in plastic EDTA (purple top) tube	Plasma (EDTA)
	• Administer 1.0 mg (total dose) TRH intravenously
	• Collect blood in plasma EDTA (purple top) tube 30 minutes later
	• Submit samples for ACTH levels (Sample handling for ACTH is outlined above)
ODST	5 pm	Serum ×2
	• Collect blood in a plain (red top) vacutainer for basal cortisol level
	• Administer 40 μg/kg of dexamethasone intramuscularly
	8 am–12 pm hours the next day (7 pm–12 am later)
	• Collect second blood sample in a plain (red top) vacutainer for second cortisol level
α-MSH	• Blood collected in EDTA vacutainer	Plasma (EDTA)
Insulin	• Collect blood in a plain (red top) vacutainer, preferably after a short overnight fast	Serum
Oral glucose challenge	• Give 0.15 mL/kg of Karo Lyte corn syrup orally	Serum
	• Collect blood in a plain (red top) vacutainer for an insulin level 60–90 minutes later

Abbreviations: ACTH, adrenocorticotropin hormone; EDTA, ethylenediaminetetraacetic acid; α-MSH, α-melanocyte-stimulating hormone; ODST, overnight dexamethasone suppression test; PPID, pituitary pars intermedia dysfunction; TRH, thyrotropin-releasing hormone.

Mc GowanTWPinchbeckGPMcGowanCMEvaluation of basal plasma α-melanocyte-stimulating hormone and adrenocorticotrophic hormone concentrations for the diagnosis of pituitary pars intermedia dysfunction from a population of aged horsesEquine Vet J2013451667322563728

 PubMed Web of Science ®Google Scholar

McFarlaneDParadisMZimmelDThe effect of geographic location, breed, and pituitary dysfunction on seasonal adrenocorticotropin and α-melanocyte-stimulating hormone plasma concentrations in horsesJ Vet Intern Med20112587288121745243

 PubMed Web of Science ®Google Scholar

CopasVENDurhamAECircannual variation in plasma adrenocorticotropic hormone concentrations in the UK in normal horses and ponies, and those with pituitary pars intermedia dysfunctionEquine Vet J201244444044321848531

 PubMed Web of Science ®Google Scholar