Endocrine- PPID and other Flashcards
Influence of feeding and other factors on adrenocorticotropin concentration and TRH stimulation test in horses and ponies
Feeding concentrate does not influence TRH stim results. Pergolide didn’t influence TRH stim results but did bACTH. Grey horses had higher pACTH
Evaluation of Seasonal Influences on ACTH Response to TRH Stimulation Test
-Accuracy of the TRH stimulation test was greater than that of basal ACTH, although specificity did not differ significantly, and sensitivity was not consistently greater year-round
-Use temporally specific DCOVs for basal and TRH-stimulated ACTH to improve diagnostic accuracy across seasons.
-Sensitivity of TRH-stimulated ACTH exceeded basal ACTH during specific months (January-May, September, November, December), supporting its use in these periods.
-During summer and autumn (July-December), high variability in TRH responses makes interpretation more challenging.
Comparison of Immunofluorescence and Chemiluminescence for Measuring ACTH in equine plasma
- give different results, particularly post TRH stim. Immunofluorescence > CL
-The exaggerated CL results post-TRH stimulation support the hypothesis that cross-reacting peptides, such as corticotropin-like intermediate lobe peptide (CLIP), interfere with CL assay results.
-The IF assay specifically targets the intact ACTH peptide, while the CL assay uses antibodies that can cross-react with CLIP (ACTH 18–39). -TRH stimulation promotes the release of multiple POMC derivatives.
-Findings suggest that ACTH may not be the dominant secretory product of the pars intermedia in some ponies, with cross-reacting POMC peptides contributing more significantly.
The IF assay’s higher specificity makes it potentially more reliable for interpreting TRH stimulation tests, but further validation is necessary. (i.e. investigation of cross reacting pepitdes)
-Agreement between assays for binary classification of PPID was moderate to very good for ponies pre- and post-TRH stimulation but varied for horses depending on the season.
Factors Affecting Basal ACTH Measurement in Domestic Equids: A Scoping Review
basal ACTH levels: breed, age, sex, time of year, sample handling, exercise, transportation, and health status.- unknown clinical significance
-Ponies and donkeys generally showed higher ACTH levels than horses, especially during autumn.
-Seasonal effects on ACTH concentrations were robust, with peaks in autumn and nadirs in spring.
-Older equids had slightly higher ACTH concentrations, but the clinical relevance of this finding in PPID diagnosis was not well established.
-Transportation, exercise, and environmental stressors can transiently increase ACTH concentrations, potentially leading to false positives.
-Gestational and reproductive status influenced ACTH levels, with increased concentrations in late pregnancy and during certain stages of the estrous cycle. This could affect diagnostic interpretations in broodmares.
-Studies showed faster degradation of ACTH in samples from PPID cases compared to controls
Investigation of Breed Differences in ACTH Concentrations in healthy horses and ponies
Shetland ponies had the highest ACTH concentrations, with levels approximately 2.67-fold higher than Thoroughbreds and 1.73-fold higher than non-Shetland pony breeds in autumn.
Non-Shetland pony breeds showed ACTH levels 1.55-fold higher than Thoroughbreds during autumn.
Reference intervals for ponies in autumn were markedly higher than those for Thoroughbreds, with upper limits that may lack clinical utility.
Used CL assay- cross reaction
The Effect of Pergolide on ACTH Response to TRH in PPID Horses
-A reduction in TRH-stimulated ACTH levels occurred in 88% of cases, indicating a positive treatment response. vs 668% basal
-50% improved their diagnostic category, with only 5% showing a deterioration in diagnostic status. 24% of cases with positive pre-treatment TRH stimulation tests achieved normalization
-The fold-increase in ACTH during TRH stimulation tests decreased significantly post-treatment. This suggests that pergolide suppresses the pituitary response to TRH rather than only reducing baseline ACTH concentrations.
-No further significant improvements in TRH-stimulated ACTH concentrations were observed in long-term follow-ups beyond 100 days
–> recommend repeat TRH stim for monitoring testing, particularly in equivocal cases
No information on correlation with clinical outcomes
Efficacy of Pergolide for Management of Equine PPID: A Systematic Review
- > 76% showing clinical improvement (subjective). One study had scoring systema nd one reduction in anagen phase hair follicles following 6 months of treatment. Variable which responded.
-A reduction in plasma ACTH concentrations was reported in 44–74% of cases, Did not always correlate with clinical improvement
-Normalisation to within reported reference intervals occurred in 28–74% of cases
-those with higher ACTH more likely to improve.
-AE: transient inappetence 33%,
ACTH as a Biomarker for PPID: Systematic Review and Meta-Analysis
-Pooled sensitivity and specificity for ACTH as a biomarker for PPID were 0.72 (95% CI: 0.62–0.82) and 0.88 (95% CI: 0.79–0.93), respectively.
-A subset of studies using a common ACTH threshold (35 pg/mL) yielded slightly lower sensitivity (0.66, 95% CI: 0.54–0.77) but comparable specificity (0.87, 95% CI: 0.74–0.94).
-Considerable variability in diagnostic accuracy was observed, influenced by study design, reference standards, and data-driven positivity thresholds.
-Case-control studies and those with clinical reference standards demonstrated higher diagnostic accuracy compared to cross-sectional designs or histopathology/dynamic testing standards.
-When combined with clinical signs, a positive ACTH test is strongly indicative of PPID. Is a poor rule out/ screening test
- warns against the use of fixed thresholds
Repeatability of TRH Stimulation Test for PPID Diagnosis in mature horses
-The TRH stimulation test demonstrated excellent repeatability in winter. Differences in plasma ACTH concentrations between test repetitions were within assay variability limits.
-The test showed lower repeatability in autumn. Larger differences between weeks 1 and 2 were observed, resulting in more misclassifications compared to winter.
-Misclassification of PPID cases was more common in autumn than in winter due to inconsistent ACTH responses after TRH stimulation.
-High specificity of diagnostic cutoffs limited false positives but led to misclassification of some borderline cases.
-Horses with PPID showed greater variability in ACTH concentrations after TRH stimulation compared to controls, particularly in autumn. Repeat testing within a short timeframe (e.g., two weeks) may be influenced by depletion of ACTH stores in melanotropes following the initial stimulation.
- Bias in winter= 2.6pg/ml, bias in autumn= 65.8
Effect of Early/Late Sampling on TRH Stimulation Results
-Plasma ACTH concentrations were significantly influenced by sampling time, with 75% of horses showing ≥10% variation in ACTH levels when samples were taken one minute early (9 minutes) or late (11 minutes) .
- 25% of cases, both early and late samples deviated by ≥10% from the 10-minute standard value.
-Sampling time discrepancies altered test interpretation in 21% of horses,
-ACTH levels peak rapidly following TRH stimulation, with individual variation in the timing and magnitude of the response. Sampling at 9 minutes resulted in higher ACTH concentrations, while sampling at 11 minutes produced lower
-Bland-Altman analysis revealed biases of +18.9 pg/mL for early sampling and -23.8 pg/mL for late sampling relative to the 10-minute standard.
-When excluding data from horses with extremely high ACTH responses (>250 pg/mL), biases remained but were reduced to +7.72 pg/mL (early) and -10.0 pg/mL (late).
Clinically and Temporally Specific Diagnostic Thresholds for Plasma ACTH in Horses
-Temporal variation in ACTH levels was confirmed, with peaks in autumn (late September to early October) and a nadir in spring (April to May).
-The indirect method used to establish thresholds bypassed the challenges of relying on pre-defined disease status, which often includes misclassification errors.
-The approach identified two populations (high-ACTH and low-ACTH) within the dataset without the need for an external gold-standard diagnostic test.
Effect of Month and Breed on Plasma ACTH Concentrations in Equids
-A circannual pattern of ACTH concentration was documented, with a nadir in April and a peak in September.
- Inter-breed differences in plasma ACTH were substantial: Arabian horses and donkeys higher ACTH May to November, Shetland ponies and Welsh breeds higher ACTH July to November.
-The annual increase in plasma ACTH appeared to commence in late April/ early May in response to increasing daylight and decreased again promptly after the late September equinox as daylength fell below 12 h per day
The observed circannual pattern aligns with photoperiodic changes: ACTH concentrations increase as daylength exceeds 14.5 hours (mid to late April) and decline after the autumn equinox (late September).
-The link between photoperiod and pituitary pars intermedia (PI) activity may reflect evolutionary adaptations to seasonal variations in environmental conditions and metabolic demands.
Higher ACTH levels in donkeys, Arabians, Shetlands, and Welsh breeds might reflect genetic or evolutionary adaptations to harsh environments:
-Insulin resistance, associated with PI activity, provides a survival advantage during periods of food scarcity.
Diagnostic thresholds for PPID must account for both seasonal and breed variations to avoid misclassification. Uniform ACTH cut-offs may lead to false positives in high-ACTH breeds (e.g., donkeys and Shetlands) and false negatives in low-ACTH breeds during non-peak months. Diagnostic interpretation should incorporate temporal and breed-specific adjustments to improve accuracy.
Clinical implications of imprecise sampling time for 10- and 30-min thyrotropin-releasing hormone stimulation tests in horses
-No significant effect of imprecise sampling (±1 minute) was observed on absolute ACTH concentrations for either, but SD in ACTH concentrations were noted between samples taken at 9 and 11 minutes for the 10-minute protocol, but not for 29 and 31 minutes in the 30-minute protocol.
-50% of horses classified as positive by the 30-minute protocol would not have been classified as positive using the 10-minute protocol. Horses with equivocal 10-minute results were generally classified as positive with the 30-minute protocol when clinical signs were considered.
-ACTH concentrations around the 30-minute mark were more stable, making this protocol less affected by sampling imprecision- narrower limits of agreement and smaller bias
-The 10-minute protocol remains useful for faster diagnostics but is more sensitive to sampling precision, necessitating strict timing adherence.
Sensitivity and Specificity of Basal Plasma ACTH for PPID Diagnosis: Systematic Review
–ACTH was reported to have good sensitivity (overall median 75.5%) and excellent specificity (overall median, 95.2%).
-Basal ACTH was found to be more effective at ruling out PPID (high specificity) than detecting it (moderate sensitivity), highlighting a risk of false negatives in some PPID cases.
-Sensitivity was lowest in studies using ungraded histopathology as the reference standard.
-Differences in study design, assay types, and diagnostic cutoffs contributed to wide inter-study variability.
-Results from studies using radioimmunoassay (RIA) assays showed significantly higher sensitivity compared to those using chemiluminescent immunoassay (CIA).
Clinical Implications of Using ACTH Cutoffs or Reference Intervals for PPID
-Clinicians should select DCOVs or RIs based on the clinical context and diagnostic goals. Use DCOVs for early detection in at-risk populations and RIs to confirm diagnoses in low-suspicion cases or for treatment decisions in competitive horses.
-TRH stimulation should be considered routine for improving diagnostic accuracy, particularly in ambiguous cases.
-Seasonal thresholds are critical for accurate interpretation, especially during periods of increased circannual variability in ACTH levels.
-DCOVs enhance sensitivity, increasing the detection of early PPID cases, but may produce false positives. Recommended for cases where missing a PPID diagnosis could have serious welfare implications, such as older horses with insulin dysregulation.
-RIs provide higher specificity, reducing false positives and unnecessary treatment, but lower sensitivity limits their ability to detect early PPID cases. Suitable for situations with lower clinical suspicion or where treatment has potential side effects, such as in athletic horses.
Relationship Between ACTH and Reproductive Performance in TB Broodmares
-conception/delivery % significantly lower in the high ACTH group than the low/intermediate (P = .02, P = .008, respectively)
-None had clinical signs of PPID or identified reproductive abnormalities.
-The number of injured vaginal and external uterine ostia was significantly higher in the high ACTH group than in the low ‘-ACTH group (P = .03) but NSD in the age
- BAD STUDY- CONCURRENT DISEASE??
Management of Pituitary Pars Intermedia Dysfunction in Practice: A Clinical Audit
- 48% laminitics positive for PPID
- Despite 78.7% of PPID-positive cases receiving pergolide treatment, over 20% were left untreated.
- 76% of positive cases treated with pergolide were monitored, 48.1% of pergolide-treated cases underwent ACTH testing within the first 1–3 months post-diagnosis,
-12% on incorrect dose, primarily under dosing
Lumbar Vertebral Bone Density is Decreased in Horses with Pituitary Pars Intermedia Dysfunction
-PPID+ horses exhibited significantly lower BMD in the lumbar vertebrae compared to both aged and young control horses.
-No significant differences were observed in BMD for weight-bearing bones (e.g., metacarpus [MC3] and metatarsus [MT3]) across groups.
-Biomechanical testing of the fourth lumbar vertebrae (L4) revealed no significant differences between PPID+ and aged control horses in force at fracture, Young’s modulus, strain, or displacement at fracture. However, variations in biomechanical measures and the small sample size may have reduced the power to detect meaningful differences.
-A significant negative correlation between PTH and trabecular BMD in the lumbar spine was noted, suggesting PTH involvement in bone loss, but further validation is required.
Translating Research into Practice: Adoption of Endocrine Diagnostic Testing in Equine Laminitis Cases
Survey of vets- Endocrine testin has changed in recent years.
99% do some endocrine testing but ACTH > Insulin/EMS
Major benefits seen in prevention and client communication. Some feeling that it reduced length of laminitis episode
Effect of Digital Hypothermia on Lamellar Inflammatory Signaling in Hyperinsulinemic Laminitis Model
- Decreased: CXCL6, CXCL8, IL-6 , IL-1β, IL-11, COX-2, total STAT3
- Increased : COX1
Small sample size and were all administered PBZ.
CDH was 30min before EHC onset
The effect of continuous digital hypothermia on lamellar energy metabolism and perfusion during laminitis development in two experimental models
CDH 30 mins before stimulating laminitis significantly decreased:
-lamellar glucose metabolism in all groups = lower lactate and pyruvate concentrations in CDHs.
- lamellar perfusion (measured by urea clearance) in control and EHC groups, but not in the OF group. (? OF inflammatory effects in the OF model counteracting the vasoconstrictive effects of CDH)
-Despite reduced perfusion, lamellar glucose concentrations were maintained in CDH limbs -> does not cause energy failure in the lamellae.
Lactate-to-Pyruvate (LP) Ratio: increased in AMB limbs of the EHC and OF models, reflecting oxidative energy dysfunction. This increase was not observed in CDH limbs, suggesting that CDH helps preserve mitochondrial function and prevents metabolic failure.
Lamellar Perfusion and Energy Metabolism in Preferential Weight-Bearing Model
-Increased load on a preferential weight-bearing (PWB) limb caused ischemia localized to the lamellar dermis, evidenced by elevated lactate-to-pyruvate (L ) ratios and decreased urea clearance.
-Adjacent sublamellar dermis was not affected, indicating the specificity of ischemic changes to lamellar tissues.
-Lamellar ischemia developed over time (28–72 hours post-increased load) and was not associated with large-vessel occlusion, suggesting a microvascular mechanism.
-The load applied in the PWB model (38.7% of body weight) reflects moderate increases seen in severely lame horses but is less than complete unilateral weight-bearing
