Dermatitis, cellulitis, and osteomyelitis caused by Aspergillus nidulans in a horse with pituitary pars intermedia dysfunction.

Clinical and histologic examination of a 12-y-old client-owned Quarter Horse gelding with pituitary pars intermedia dysfunction revealed dermatitis, cellulitis, and osteomyelitis caused by Aspergillus nidulans, confirmed by a PCR assay. This novel presentation of a fungal disease in a horse was characterized by aggressive local invasion and failure to respond to all medical therapy attempted over a 1-y period. Treatments included systemic and topical antifungals, anti-inflammatories, and use of cellular matrices. Surgical excision was not attempted but should be strongly considered early in the disease process in similar cases if clean margins can be achieved. Postmortem findings were of locally aggressive disease with no dissemination.

Factors affecting measurement of basal adrenocorticotropic hormone in adult domestic equids: A scoping review.

Measurement of basal adrenocorticotropic hormone (ACTH) concentration is the most commonly used diagnostic test for pituitary pars intermedia dysfunction (PPID). Although several pre-analytical and analytical factors have been reported to affect basal ACTH concentrations in equids, the extent to which these have been evaluated in the context of PPID diagnosis is unclear. The objectives of this scoping review were to identify and systematically chart current evidence about pre-analytical and analytical factors affecting basal ACTH concentrations in adult domestic equids. Systematic searches of electronic databases and conference proceedings were undertaken in June 2022, repeated in October 2022 and updated in August 2023. English language publications published prior to these dates were included. Screening and data extraction were undertaken individually by the authors, using predefined criteria and a modified scoping review data extraction template. After removal of duplicates, 903 publications were identified, of which 235 abstracts were screened for eligibility and 134 publications met inclusion criteria. Time of year, exercise, breed/type and transportation were the factors most frequently associated with significant increases in ACTH concentration (n = 26, 16, 13 and 10 publications, respectively). Only 25 publications reported inclusion of PPID cases in the study population, therefore the relationship between many factors affecting basal ACTH concentration and diagnostic accuracy for PPID remains undefined. However, several factors were identified that could impact interpretation of basal ACTH results. Findings also highlight the need for detailed reporting of pre-analytical and analytical conditions in future research to facilitate translation of evidence to practice.

Influence of feeding and other factors on adrenocorticotropin concentration and thyrotropin-releasing hormone stimulation test in horses and ponies.

BACKGROUND: The basal (bACTH) and post-thyrotropin-releasing hormone stimulation concentration of adrenocorticotropin (pACTH) are recommended for diagnosis of pituitary pars intermedia dysfunction (PPID). Many factors influence bACTH (e.g., disease, age, month) and some affect the results only in autumn (e.g., breed, colour, sex). There are discrepancies about the impact of feeding on b/pACTH. OBJECTIVES: To determine whether feeding, month, age, breed, colour, sex and body condition score affect b/pACTH. STUDY DESIGN: Prospective crossover. METHODS: Sixty-one animals were divided into groups: healthy, PPID, treated-PPID. The b/pACTH was measured three times (1 mg protirelin; blood collection after 10 min; mid-November to mid-July) after different feedings: fasting, hay, hay + grain. Friedman's test was applied to evaluate the influence of feeding on b/pACTH and linear mixed model to evaluate impact of further factors. RESULTS: The b/pACTH was not significantly affected by feeding (p = 0.7/0.5). The bACTH was lowest in healthy (29.3 pg/mL, CI 9-49.5 pg/mL) and highest in PPID-group (58.9 pg/mL, CI 39.7-78.1 pg/mL). The pACTH was significantly lower in healthy (396.7 pg/mL, CI 283.2-510.1 pg/mL) compared to PPID (588.4 pg/mL, CI 480.7-696.2 pg/mL) and treated-PPID group (683.1 pg/mL, CI 585.9-780.4 pg/mL), highest in July (881.2 pg/mL, CI 626.3-1136.3 pg/mL) and higher in grey (723.5 pg/mL, CI 577.5-869.4 pg/mL) than other colours (338.7 pg/mL, CI 324.8-452.5 pg/mL). The size of effect for those variables was >0.5. MAIN LIMITATIONS: Small number of animals, subsequent bACTH measurements were significantly lower in each horse. CONCLUSIONS: There was no evidence that feeding influences the b/pACTH. There was evidence that pergolide affects the bACTH but it had little effect on pACTH. Further investigation of the impact of month and coat colour on b/pACTH is warranted to better interpret the results.

Clinical implications of imprecise sampling time for 10- and 30-min thyrotropin-releasing hormone stimulation tests in horses.

BACKGROUND: The thyrotropin-releasing hormone (TRH) stimulation test is used to diagnose pituitary pars intermedia dysfunction (PPID) using 10- or 30-min protocols. Imprecise sampling time for the 10-min protocol can lead to misdiagnoses. OBJECTIVES: To determine the effect of imprecise sampling time for the 30-min protocol of the TRH stimulation test. STUDY DESIGN: In vivo experiment. METHODS: Plasma immunoreactive adrenocorticotropin (ACTH) concentrations were measured 9, 10, 11, 29, 30 and 31 min after intravenous administration of 1 mg of TRH in 15 control and 12 PPID horses. Differences in ACTH concentrations between sampling times, variability in ACTH concentrations between protocols, and diagnostic classification of PPID were assessed using Friedman's test, Bland-Altman plots, and Fisher's exact test, respectively, with 95% confidence intervals reported and significance set at p < 0.05. RESULTS: Imprecise sampling time resulted in variable ACTH concentrations, but significant differences in absolute ACTH concentrations were not detected for imprecise sampling within each protocol or between protocols. Imprecise sampling changed PPID diagnostic classification for 3/27 (11 [4-28] %) horses for both protocols. Using the 30-min protocol as a reference, 1/12 (8 [1-35] %) horses returned a negative test result and 5/12 (42 [19-68] %) horses returned equivocal test results that would be considered positive in practice due to the presence of supportive clinical signs. MAIN LIMITATIONS: Limited sample size and inter-horse variability reduced the ability to detect small but potentially relevant differences. CONCLUSIONS: Overall, the impact of imprecise sampling was not significantly different between the 10- and 30-min TRH stimulation test protocols. However, diagnostic classification for PPID would have varied between the 10- and 30-min protocols in this population, if clinical signs had been ignored. Precise timing during TRH stimulation tests and contextual interpretation of ACTH concentrations remain fundamental for the diagnosis of PPID.

BEVA primary care clinical guidelines: Diagnosis and management of equine pituitary pars intermedia dysfunction.

BACKGROUND: Pituitary pars intermedia dysfunction (PPID) is a prevalent, age-related chronic disorder in equids. Diagnosis of PPID can be challenging because of its broad spectrum of clinical presentations and disparate published diagnostic criteria, and there are limited available treatment options. OBJECTIVES: To develop evidence-based primary care guidelines for the diagnosis and treatment of equine PPID based on the available literature. STUDY DESIGN: Evidence-based clinical guideline using the Grading of Recommendations, Assessment, Development and Evaluation (GRADE) framework. METHODS: Research questions were proposed by a panel of veterinarians and developed into PICO or another structured format. VetSRev and Veterinary Evidence were searched for evidence summaries, and systematic searches of the NCBI PubMed and CAB Direct databases were conducted using keyword searches in July 2022 and updated in January 2023. The evidence was evaluated using the GRADE framework. RESULTS AND RECOMMENDATIONS: The research questions were categorised into four areas: (A) Case selection for diagnostic testing, pre-test probability and diagnostic test accuracy, (B) interpretation of test results, (C) pharmacological treatments and other treatment/management options and (D) monitoring treated cases. Relevant veterinary publications were identified and assessed using the GRADE criteria. The results were developed into recommendations: (A) Case selection for diagnostic testing and diagnostic test accuracy: (i) The prevalence of PPID in equids aged ≥15 years is between 21% and 27%; (ii) hypertrichosis or delayed/incomplete hair coat shedding provides a high index of clinical suspicion for PPID; (iii) the combination of clinical signs and age informs the index of clinical suspicion prior to diagnostic testing; (iv) estimated pre-test probability of PPID should be considered in interpretation of diagnostic test results; (v) pre-test probability of PPID is low in equids aged <10 years; (vi) both pre-test probability of disease and season of testing have strong influence on the ability to diagnose PPID using basal adrenocorticotropic hormone (ACTH) or ACTH after thyrotropin-releasing hormone (TRH) stimulation. The overall diagnostic accuracy of basal ACTH concentrations for diagnosing PPID ranged between 88% and 92% in the autumn and 70% and 86% in the non-autumn, depending on the pre-test probability. Based on a single study, the overall diagnostic accuracy of ACTH concentrations in response to TRH after 30 minutes for diagnosing PPID ranged between 92% and 98% in the autumn and 90% and 94% in the non-autumn, depending on the pre-test probability. Thus, it should be remembered that the risk of a false positive result increases in situations where there is a low pre-test probability, which could mean that treatment is initiated for PPID without checking for a more likely alternative diagnosis. This could compromise horse welfare due to the commencement of lifelong therapy and/or failing to identify and treat an alternative potentially life-threatening condition. (B) Interpretation of diagnostic tests: (i) There is a significant effect of breed on plasma ACTH concentration, particularly in the autumn with markedly higher ACTH concentrations in some but not all 'thrifty' breeds; (ii) basal and/or post-TRH ACTH concentrations may also be affected by latitude/location, diet/feeding, coat colour, critical illness and trailer transport; (iii) mild pain is unlikely to have a large effect on basal ACTH, but caution may be required for more severe pain; (iv) determining diagnostic thresholds that allow for all possible contributory factors is not practical; therefore, the use of equivocal ranges is supported; (v) dynamic insulin testing and TRH stimulation testing may be combined, but TRH stimulation testing should not immediately follow an oral sugar test; (vi) equids with PPID and hyperinsulinaemia appear to be at higher risk of laminitis, but ACTH is not an independent predictor of laminitis risk. (C) Pharmacologic treatments and other treatment/management options: (i) Pergolide improves most clinical signs associated with PPID in the majority of affected animals; (ii) Pergolide treatment lowers basal ACTH concentrations and improves the ACTH response to TRH in many animals, but measures of insulin dysregulation (ID) are not altered in most cases; (iii) chasteberry has no effect on ACTH concentrations and there is no benefit to adding chasteberry to pergolide therapy; (iv) combination of cyproheptadine with pergolide is not superior to pergolide alone; (v) there is no evidence that pergolide has adverse cardiac effects in horses; (vi) Pergolide does not affect insulin sensitivity. (D) Monitoring pergolide-treated cases: (i) Hormone assays provide a crude indication of pituitary control in response to pergolide therapy, however it is unknown whether monitoring of ACTH concentrations and titrating of pergolide doses accordingly is associated with improved endocrinological or clinical outcome; (ii) it is unknown whether monitoring the ACTH response to TRH or clinical signs is associated with an improved outcome; (iii) there is very weak evidence to suggest that increasing pergolide dose in autumn months may be beneficial; (iv) there is little advantage in waiting for more than a month to perform follow-up endocrine testing following initiation of pergolide therapy; there may be merit in performing repeat tests sooner; (v) timing of sampling in relation to pergolide dosing does not confound measurement of ACTH concentration; (vi) there is no evidence that making changes after interpretation of ACTH concentrations measured at certain times of the year is associated with improved outcomes; (vii) evidence is very limited, however, compliance with PPID treatment appears to be poor and it is unclear whether this influences clinical outcome; (viii) evidence is very limited, but horses with clinical signs of PPID are likely to shed more nematode eggs than horses without clinical signs of PPID; it is unclear whether this results in an increased risk of parasitic disease or whether there is a need for more frequent assessment of faecal worm egg counts. MAIN LIMITATIONS: Limited relevant publications in the veterinary scientific literature. CONCLUSIONS: These findings should be used to inform decision-making in equine primary care practice.

Lumbar vertebral bone density is decreased in horses with pituitary pars intermedia dysfunction.

BACKGROUND: Pathological fractures have been reported in equids with pituitary pars intermedia dysfunction (PPID) but their prevalence and pathogenesis is unknown. OBJECTIVES: To compare: (1) bone mineral density (BMD) in weight bearing and nonweight bearing bones in PPID+ equids and aged and young PPID- controls; and (2) biomechanical properties of the fourth lumbar vertebral body in PPID+ equids and aged PPID- equids. STUDY DESIGN: Case-control study: five PPID+ equids and six aged and four young PPID- control horses. METHODS: PPID status was based on clinical signs and necropsy examination of the pituitary gland (PG). The lumbar vertebral column, right front third metacarpus (MC3), left hind third metatarsus (MT3), and PG were removed after euthanasia. BMD was determined by quantitative computed tomography of regions of interest (ROI) in each bone and biomechanical testing was performed on the fourth lumbar vertebral body. Serum concentrations of parathormone (PTH), ionised Ca++ , 25-hydroxyvitamin D, and osteocalcin (OC) were also measured. Data were analysed using one-way ANOVA and correlation analyses. RESULTS: BMD of trabecular and cortical regions of interest (ROI) of the third, fourth (L4), and fifth lumbar vertebrae were significantly lower in PPID+ equids as compared with aged (p < 0. 001) and young (p < 0.01) PPID- controls. In contrast, no differences were found in BMD of trabecular or cortical ROIs of MC3 and MT3 between groups. No differences were detected in force at fracture, displacement at fracture, Young's modulus or strain of L4 between PPID+ and aged PPID- horses. No differences were found in serum PTH, ionised Ca++ , 25-hydroxyvitamin D, or OC concentrations between groups. MAIN LIMITATIONS: Limited number of equids studied and variation in test results. CONCLUSIONS: BMD of nonweight bearing bones can be decreased with PPID and could increase risk of developing pathological fractures.

Diagnosis of equine pituitary pars intermedia dysfunction.

Equine pituitary pars intermedia dysfunction (PPID) is common in aged horses. The majority of horses respond well to treatment, but treatment is lifelong, meaning accurate diagnosis of PPID is important. Similar to any condition, there is no perfect laboratory test to diagnose PPID and accuracy is affected by the characteristics of the population in which the test is being evaluated. This review details the importance of consideration of clinical factors and diagnostic test accuracy. Basal adrenocorticotrophic hormone (ACTH) concentration is used most frequently in practice and has very good diagnostic accuracy when used in combination with clinical judgement and the correct application of diagnostic thresholds. The thyrotropin-releasing hormone stimulation test can be used in horses with equivocal test results following basal ACTH testing, or to evaluate subtle cases due to its improved accuracy.

Evaluation of seasonal influences on adrenocorticotropic hormone response to the thyrotropin-releasing hormone stimulation test and its accuracy for diagnosis of pituitary pars intermedia dysfunction.

Pituitary pars intermedia dysfunction (PPID) is an age-related neurodegenerative disorder, affecting >20 % of older horses. There is a need for improved endocrine tests for early disease detection, and the thyrotropin-releasing hormone (TRH) stimulation test has been recommended for diagnosis of early or mild cases. However, it is currently not recommended for year-round use due to marked seasonal variability. The aims of this cohort study were to evaluate effects of month and season on adrenocorticotropic hormone (ACTH) responses to TRH stimulation and to derive monthly cut-offs for PPID diagnosis. Sixty-three horses were assigned to control (n = 17), subclinical PPID (n = 21) and clinical PPID (n = 25) groups, based on a composite reference standard that combined clinical history and examination findings with endocrine test results. TRH stimulation tests were performed monthly for a 12-month period. Circannual changes were evaluated with one- and two-way repeated-measures analysis of variance and receiver operating characteristic curve analysis was used to derive cut-off values for basal and TRH-stimulated ACTH. TRH-stimulated ACTH concentrations were lowest in February-May and highest in August-October. Specificity of both basal and 30 min post-TRH ACTH was generally higher than sensitivity, and TRH stimulation had improved diagnostic accuracy compared to basal ACTH, although its sensitivity was not significantly greater year-round. TRH stimulation tests yielded considerably more positive results than basal ACTH in the subclinical group, but few additional positive results in clinical PPID cases. There were large differences between cut-offs that maximised sensitivity or specificity for TRH-stimulated ACTH, highlighting the importance of considering clinical presentation alongside test results in diagnostic decision-making.

Cytodifferentiation of Wulzen's cone of mature male sheep hypophysis cerebri with special emphasis on its parenchymal correlations with the adjacent pars distalis, pars intermedia and pars nervosa.

Background: Hypophysis cerebri is considered the master endocrine gland as it plays a critical role in influencing and controlling the vitality of other endocrine organs via several hormones secretion. Aim: The present study was performed to clarify the localization of Wulzen's cone (WC) within sheep hypophysis and cytodifferentiation of the glandular cells filling cone parenchyma with particular emphasis on the cone correlations with adjacent pars distalis (pd), pars intermedia (pi), and pars nervosa (pn). Methods: Pituitaries were collected and processed histologically, then subjected to different combinations of special stains; Br-AB- OFG., PFA-AB-PAS-OG., PAS-Orange G., Orange G- Acid Fuchsin- Light Green, Bielschowsky technique, Masson's trichrome & Gomori's reticulin. Results: A sagittal section through the pituitaries revealed a well-developed cone of glandular cells protruding from the pi like a tongue plate towards the hypophyseal cleft in the neighborhood of the pd and behind the pn. Resembling the pd, various glandular cells were distinguished in the cone; chromophobes and chromophils of acidophils & basophils. The cone is mainly formed from acidophils intermingled with the chromophobes. Meanwhile, basophils were primarily localized at the most anterior & posterior parts of the cone. In front of the cone, pd were localized, resembling a wing-shaped and filled with several categorized glandular cells; chromophobes and chromophils. Upper to the cone, pi were localized and composed mainly of weakly basophilic cuboidal or polygonal cells arranged in parallel cords or follicles. Behind the cone, pn was localized as a ventral outpouching of the brain floor-like water drop. Unlike the cone, it was devoid of any glandular secretory cells or nerve cells but consisted mainly of unmyelinated nerve fibers, herring bodies, and pituicytes. Conclusion: WC is present and well-developed in sheep adenohypophysis. Various glandular cells were distinguished, filling the cone, chromophobes, and chromophils of acidophils & basophils that were typically similar to the glandular cells of pd but with different distributions.

Correlation of pituitary histomorphometry with dopamine and dopamine D2 receptor expression in horses with pituitary pars intermedia dysfunction.

Pituitary pars intermedia dysfunction (PPID) is an endocrinopathy commonly affecting old horses. It is a spontaneously occurring, progressive disease that is still poorly understood. Previous studies have observed neurodegeneration of the dopaminergic inhibition of melanotrophs, which leads to decreased dopamine (DA) in the pars intermedia (PI) and increased pro-opiomelanocortin-derived peptides circulating in plasma. However, rats knockout for the dopamine D2 receptor (D2r) similarly develop PI hypertrophy and hyperplasia. Thus, based on the current pathophysiological theory of PPID, whether the decreased DA or the D2r dysfunction leads to PPID is still unclear. To test this, a total of 28 retrospective cases of horses with PPID were collected, graded and the expression of tyrosine hydroxylase (TH) and D2r in the PI were determined. The histological and immunohistochemical results demonstrated that horses with higher tumor histological grades had reduced TH expression with increased D2r immunoreactivity colocalized in the PI (p < 0.001, p < 0.05 respectively). This correlation supports the role of DA in the pathogenesis of continuous unregulated proliferation of neoplastic cells in PI and indicates the efficiency of D2r agonists as a treatment for PPID.

Development and Evaluation of a Muscle Atrophy Scoring System (MASS) for Horses.

Loss of skeletal muscle mass likely compromises performance and welfare in horses and thus routine monitoring would be valuable. Currently available methods to assess muscle mass require expert knowledge and are often expensive. To provide a simple method, a muscle atrophy scoring system (MASS) was created and tested by three evaluators (raters) in 38 horses of varying age, breed, and health status. Inter-rater agreement on atrophy scores was in the good-to-excellent range for ratings of the neck (ICC = 0.62), back (ICC = 0.62) and hind (ICC = 0.76) regions but was poor for the abdominal region (ICC = 0.29). Due to this low agreement, the abdominal region was excluded from further analysis. Associations between muscle atrophy scores and age, pituitary pars intermedia dysfunction (PPID) status, and body composition indicators, including weight and estimated fat-free mass (FFM), were examined. Weight was inversely associated with neck, back and hind muscle atrophy scores (ß = -0.008, ß = -0.008, ß = -0.009, respectively; all P <0.001), but estimated FFM was not associated with muscle atrophy scores at any region (P >0.05). Age was positively related to neck (ß = 0.030, P <0.01), back (ß = 0.037, P <0.001) and hind (ß = 0.040, P <0.001) muscle atrophy scores. PPID-positive horses (n = 4) had higher muscle atrophy scores than PPID-negative horses (n = 23), even after adjusting for age (P <0.05). This data suggests that neck, back and hind region evaluations by individual raters likely have acceptable reliability. In addition, these findings support further evaluation of the potential benefits of the MASS to identify and monitor muscle atrophy in horses.

Effect of early or late blood sampling on thyrotropin releasing hormone stimulation test results in horses.

BACKGROUND: Diagnosis of pituitary pars intermedia dysfunction (PPID) using the thyrotropin-releasing hormone (TRH) stimulation test requires blood collection 10 minutes after TRH injection; it is unknown if small differences in timing affect test results. OBJECTIVE: To determine whether early or late sampling results in a significant (≥10%) difference in plasma adrenocorticotropic hormone (ACTH) concentration compared to standard 10-minute sampling. ANIMALS: Twenty-four healthy adult horses with unknown PPID status. METHODS: In this prospective study, subjects underwent a single TRH stimulation test, with blood collected exactly 9 minutes (early), 10 minutes (standard), and 11 minutes (late) after injection. ACTH was measured by chemiluminescent immunoassay. Two aliquots of the 10-minute plasma sample were analyzed separately to assess intra-assay variability. Data were reported descriptively and bias was calculated using Bland-Altman plots. Significance was set at P = .05. RESULTS: Minor variability was observed between the paired 10-minute sample aliquots (range, 0%-6%; median 3%). Overall variability of early or late samples compared to the corresponding paired (average) 10-minute standard concentration ranged from 0% to 92% (median 10%). Seventy-five percent of horses (18/24) tested had at least 1 early or late reading that differed by ≥10% from its corresponding 10-minute standard concentration, and 21% of horses (5/24) would have a different interpretation of testing result with either early or late sampling. Incidence of ≥10% variability was independent of PPID status (P = .59). CONCLUSIONS AND CLINICAL IMPORTANCE: Precise timing of sample collection is critical to ensure accurate assessment of PPID status given the observation of significant variability associated with minor alterations in timing of sample collection.

The accuracy of ACTH as a biomarker for pituitary pars intermedia dysfunction in horses: A systematic review and meta-analysis.

BACKGROUND: Accuracy of baseline ACTH for the diagnosis of PPID in horses varies between studies. OBJECTIVES: To estimate the diagnostic accuracy of ACTH as a biomarker for PPID in adult horses and appraise potential causes of heterogeneity. STUDY DESIGN: Systematic review and meta-analysis. METHODS: A literature review identified studies reporting diagnostic accuracy data for extraction. Risk of bias was evaluated using QUADAS-2. Two random-effects models, the hierarchical summary receiver operating curve (HSROC) and the bivariate binomial normal model (BBN) were used to pool accuracy measurements. We performed meta-regression using study-level variables. The impact of diagnostic test accuracy on the frequency of false-positive and false-negative results at various pretest probabilities was calculated using the BBN model's accuracy results. RESULTS: Patient selection and index test evaluation demonstrated significant risk of bias. Mean and 95% confidence intervals for sensitivity and specificity for all studies (n = 11) based upon the HSROC model were (0.72, 95% CI: 0.62 to 0.82) and (0.88, 95% CI: 0.79 to 0.93), respectively. When studies with a common positivity threshold of 35 pg/mL ACTH were evaluated (n = 6), sensitivity and specificity were (0.66, 95% CI:0.54 to 0.77) and (0.87, 95% CI: 0.74 to 0.94). In a hypothetical group of one thousand horses with PPID prevalence of 2%, 20%, and 90%, the frequency of resulting false-positive and false-negatives would be (127 and 7), (104 and 68) and (13 and 306), respectively. Factors leading to increased accuracy were case-control design, clinical reference standard and data-driven choice of ACTH threshold. MAIN LIMITATIONS: A small number of primary studies (n = 11) were available, demonstrating significant biases. CONCLUSIONS: Less biased studies examining diagnostic accuracy of ACTH are needed. In horses with a high pretest probability of PPID, ACTH may be a functional "rule-in" test. Baseline ACTH is not recommended for screening purposes or use in horses without clinical signs of PPID.

Impact of blue light therapy on plasma adrenocorticotropic hormone (ACTH) and hypertrichosis in horses with pituitary pars intermedia dysfunction.

Blue light therapy can be used in horses to alter the natural photoperiod and inhibit winter hair coat growth. Seasonal increases in ACTH occur in the fall season but are exaggerated in horses with pituitary pars intermedia dysfunction (PPID). Additionally, PPID horses frequently present with hypertrichosis. Thus, blue light therapy was proposed as a potential management tool for hypertrichosis and for investigating the impact of photoperiod manipulation on ACTH. Eighteen PPID horses, aged 18 to 31 yr, from a university-owned research herd were selected and assigned to either the control group (n = 10) or the treatment (blue light therapy) group (n = 8) based on age and clinical history, which included the results of multiple endocrine tests. Consistent daylength of approximately 14.5 h was maintained for the treated horses from July 15 through approximately late October via the extension of natural daylength using wearable masks that provided short wavelength blue light (465 nm) to 1 eye. The control group was exposed to only the natural photoperiod during this time. All horses were housed on the same farm and remained on pasture for the duration of the study. On Day 0, thyrotropin-releasing hormone (TRH) stimulation tests were performed to confirm PPID status; there were no differences between the 2 groups in resting plasma ACTH or plasma ACTH at 10 min after TRH administration. To determine an effect of treatment on ACTH, blood was collected via jugular venipuncture for measurement of ACTH at sequential timepoints over a 16-h period in mid-October. Hair weights were also assessed throughout the study. No differences in resting plasma ACTH were observed between the 2 groups across the seasonal analysis (July and October) or during the 16-h testing. The PPID horses receiving blue light therapy had lighter hair weights compared to the PPID control horses. These results suggest that blue light therapy does not alter ACTH concentrations but could potentially be used as an additional management tool for hypertrichosis in PPID horses. Manipulation of the photoperiod using blue light therapy did not affect seasonal changes in ACTH in this study.

Repeatability of a thyrotropin-releasing hormone stimulation test for diagnosis of pituitary pars intermedia dysfunction in mature horses.

BACKGROUND: Pituitary pars intermedia dysfunction (PPID) is a common endocrinopathy of horses diagnosed with a thyrotropin-releasing hormone (TRH) stimulation test. HYPOTHESIS/OBJECTIVES: Describe the repeatability of TRH stimulation in horses with and without PPID in winter and autumn. ANIMALS: Twenty adult horses; 6 controls and 6 with PPID tested in autumn, 8 controls and 6 with PPID tested in winter with 3 controls and 3 with PPID tested in both seasons. METHODS: Thyrotropin-releasing hormone stimulation was performed on 2 consecutive occasions, 1 week before and 1 week after the winter solstice and the autumn equinox. Blood was collected before and 30 minutes after IV injection of 1 mg of TRH. ACTH concentration was determined by a chemiluminescent assay. Repeatability and test-retest reliability were assessed by repeated measures analysis of variance, intraclass correlation coefficient and within-horse coefficients of variation (CV). Bland-Altman plots were generated to visualize agreement between repetitions. RESULTS: In winter, no week effect was detected on the results of the TRH simulation and the test had an excellent test-retest reliability. In autumn, after-TRH ACTH concentrations were significantly lower on week 2 (P = .02) and the test only had a good test-retest reliability. There were significantly larger within-horse CV during autumn (P = .04) and after TRH stimulation (P = .04). There were 2 misclassifications in winter and 4 in autumn. CONCLUSIONS AND CLINICAL IMPORTANCE: The TRH stimulation test was repeatable when performed 2 weeks apart in winter; however, in autumn, more variability in after-TRH ACTH concentrations resulted in decreased repeatability.

Preliminary study on the effects of pergolide on left ventricular function in the horses with pituitary pars intermedia dysfunction.

BACKGROUND: Pituitary pars intermedia dysfunction (PPID), a neurodegenerative disease leading to reduced dopamine production, is a common disease in aged horses. The treatment is based on administration of the dopamine agonist pergolide. This drug has been related to valvular fibrosis in humans, but the cardiovascular effect of this drug has not yet been investigated in horses. OBJECTIVES: To determine whether pergolide induces valvular disease in horses or affects the cardiac function. METHODS: Standard, tissue Doppler (TDE) and two-dimensional speckle tracking (STE) echocardiography were performed in horses with diagnosed PPID based on adrenocorticotropic hormone dosage. Measurements taken in horses treated with pergolide were compared with those from untreated horses with nonparametric t-tests. Furthermore, measurements from follow-up examinations performed at least three months after the initial exam were compared with a Wilcoxon signed rank test for repeated measurements in each group. RESULTS: Twenty-three horses were included. None of the 12 horses under treatment developed valvular regurgitation. Furthermore, no differences in the measurements of the left ventricular systolic or diastolic function could be seen between the group of horses with treatment and those without treatment. Measurements taken in the follow-up exam did not differ compared to those taken in the initial exam in both groups. CONCLUSIONS: No changes of the left ventricular function assessed by TDE and STE could be shown in a small population of horses with confirmed PPID. Treatment with pergolide did not affect the ventricular function nor induce valvular disease.

Equine pituitary pars intermedia dysfunction: a spontaneous model of synucleinopathy.

Equine pituitary pars intermedia dysfunction (PPID) is a common endocrine disease of aged horses that shows a similar pathophysiology as Parkinson's Disease (PD) with increased levels of α-synuclein (α-syn). While α-syn is thought to play a pathogenic role in horses with PPID, it is unclear if α-syn is also misfolded in the pars intermedia and could similarly promote self-aggregation and propagation. Consequently, α-syn was isolated from the pars intermedia from groups of healthy young and aged horses, and aged PPID-afflicted horses. Seeding experiments confirmed the prion-like properties of α-syn isolated from PPID-afflicted horses. Next, detection of α-syn fibrils in pars intermedia via transmission electron microscopy (TEM) was exclusive to PPID-afflicted horses. A bank of fragment peptides was designed to further characterize equine α-syn misfolding. Region 62-87 of equine and human α-syn peptides was found to be most prone to aggregation according to Tango bioinformatic program and kinetics of aggregation via a thioflavin T fluorescence assay. In both species, fragment peptide 62-87 is capable of generating mature fibrils as demonstrated by TEM. The combined animal, bioinformatic, and biophysical studies provide evidence that equine α-syn is misfolded in PPID horses.

Evaluation of the sensitivity and specificity of basal plasma adrenocorticotrophic hormone concentration for diagnosing pituitary pars intermedia dysfunction in horses: A systematic review.

Measurement of basal adrenocorticotrophic hormone (ACTH) is currently used to diagnose pituitary pars intermedia dysfunction (PPID) in horses, yet a systematic review of the evidence for its use has not been undertaken. This study aimed to systematically review evidence regarding the sensitivity and specificity of the basal ACTH diagnostic test. Electronic databases were systematically searched in January 2019, September 2020 and January 2021, for English language publications published prior to these dates. Screening, data extraction and quality assessment of publications was undertaken by the authors using predefined criteria. Study design, methodology and information reported in included studies were assessed using Standards for Reporting of Diagnostic Accuracy (STARD) checklists. Risk of bias and applicability were appraised using the Quality Assessment tool for Diagnostic Accuracy Studies (QUADAS-2) quality assessment tool. Due to identified biases and marked between-study variations, meta-analysis was not undertaken. After removal of duplicates, 415 publications were identified, of which 25 were evaluated in full, with 11 of these meeting inclusion criteria. In most studies, basal ACTH was reported to have good sensitivity (overall median 75.5%; interquartile range [IQR], 64.0-86.5%; range, 36.0-100%) and excellent specificity (overall median, 95.2%; IQR, 84.2-98.9%; range, 63.3-100%). However, QUADAS-2 and STARD assessment highlighted that studies did not utilise optimal study design and/or study populations for the evaluation of a diagnostic test and the majority were subject to bias, or provided insufficient information to fully assess possible biases. Based on this review, basal ACTH performed better at ruling out PPID than detecting it.

Relationship between endogenous plasma adrenocorticotropic hormone concentration and reproductive performance in Thoroughbred broodmares.

BACKGROUND: Pituitary pars intermedia dysfunction (PPID) is an endocrine disorder the clinical signs of which include infertility, but few reports have examined the relationship between PPID and reproductive performance in broodmares. HYPOTHESIS/OBJECTIVE: Broodmares with infertility of unknown etiology were screened for PPID using baseline endogenous plasma ACTH concentrations, and its relationship with subsequent reproductive performance was analyzed. ANIMALS: Sixty-seven Thoroughbred broodmares. METHODS: Adrenocorticotropic hormone concentrations were measured in autumn. The broodmares were divided into 3 groups based on endogenous plasma ACTH concentration (low, <50 pg/mL; intermediate 50-100 pg/mL; and high >100 pg/mL) as recommended by the Equine Endocrinology Group. We compared these results with those of other blood tests, clinical examinations, subsequent conception, and frequency of normal delivery. RESULTS: The numbers of horses per group (percentage) were 22 (32.8%), 20 (29.9%), and 25 (37.3%). The mean ± SD ages (years) were 11.1 ± 3.4, 12.1 ± 4.5, and 13.0 ± 4.3, with no significant difference among groups. Mean ± SD plasma cortisol concentrations (µg/dL) were 4.0 ± 1.6, 7.1 ± 1.4, and 7.6 ± 1.9, with the intermediate and high ACTH groups having significantly higher results than the low ACTH group (P < .001). Conception rates were 77.3%, 89.5%, and 56.5% and normal delivery rates were 77.2%, 84.2%, and 43.5% with the percentage of each significantly lower in the high ACTH group (P = .02, P = .008, respectively). CONCLUSIONS AND CLINICAL IMPORTANCE: The study group of infertile broodmares may include horses with PPID. The reproductive performance of the high ACTH group was significantly lower than the other groups. Early diagnosis and treatment of infertile broodmares by screening plasma ACTH concentrations could help improve reproductive performance.

Pergolide dosing compliance and factors affecting the laboratory control of equine pituitary pars intermedia dysfunction.

BACKGROUND: Equine pituitary pars intermedia dysfunction (PPID) is treated with daily pergolide therapy. Owner compliance and its effect on PPID control have not been previously investigated. METHODS: Clinical records were searched to identify the sample of animals with PPID treated with pergolide from 2016 to 2019. The signalment was noted and the dose of pergolide received calculated. Animals were classified as compliant (receiving ≥90% of the veterinarian recommended dose of pergolide) or non-compliant, and as controlled (follow-up basal adrenocorticotrophic hormone concentrations within the reference range) or not. RESULTS: In total, 110 animals were included. The majority (85%) were ≥16 years (mean ± SD 19.8 ± 4.4 years); the most common breeds were Cob (18%), Thoroughbred (16%) and Welsh (15%); 37% were female and 63% male. Overall, 48% were compliant and 52% non-compliant. There was no significant effect of compliance on laboratory control. Of those that were compliant, 74% were controlled, while 67% of non-compliant animals were controlled. Univariable analysis revealed a significant (p < 0.001) effect of age and breed on compliance and control, and of sex on control. On multivariable analysis, only age (compliance) and breed (compliance and control) were retained in the final model. CONCLUSION: Only half of animals received the recommended pergolide dose; however, this did not affect laboratory control of PPID.