Evaluation of individual low-dose dexamethasone suppression test patterns in naturally occurring hyperadrenocorticism in dogs

Frequency of low-dose dexamethasone suppression test (LDDST) response patterns and their correlation with clinicopathologic signs in dogs suspected of having Cushing's syndrome: A retrospective study

A retrospective cross-sectional study was conducted to assess the frequency of low-dose dexamethasone suppression test (LDDST) patterns in canine patients that had clinicopathologic signs consistent with Cushing's syndrome (CS). Medical records for patients of interest (N = 128) were reviewed between January 2014 and December 2020 to analyse and classify LDDST results based upon the following patterns: lack of suppression, partial suppression, complete suppression, escape, or inverse. Complete suppression, lack of suppression, partial suppression, escape, and inverse patterns were identified in 39.1%, 31.2%, 14.1%, 10.1% and 5.5% of cases respectively. LDDST results were also evaluated with respect to clinical signs, serum alkaline phosphatase (ALP) activity, urine specific gravity (USG) and adrenal ultrasonographic findings. There was no association between LDDST patterns and clinical signs (p = 0.11), increased ALP (p = 0.32), USG (p = 0.33) or adrenal ultrasonographic findings (p = 0.19). In all dogs that demonstrated complete suppression or an inverse pattern, CS was excluded by the attending clinician. The diagnosis of CS was also excluded without further exploration in 23.1%, 7.5% and 5.6% of dogs that demonstrated an escape pattern, lack of suppression and partial suppression pattern, respectively. These results suggest that the clinical significance of LDDST patterns, particularly escape and inverse patterns, are misunderstood by some clinicians, leading them to prematurely exclude the diagnosis of CS.

Lipoprotein profiles in Miniature Schnauzer dogs with idiopathic hypertriglyceridemia and hypercortisolism

Miniature Schnauzer dogs (MSs) are predisposed to both idiopathic hypertriglyceridemia (iHTG) and hypercortisolism (HCort). To our knowledge, the lipoprotein profiles of MSs with iHTG have not been compared to those with HCort. We analyzed cholesterol and triglyceride concentrations and lipoprotein fractions in 4 groups of MSs: normotriglyceridemia (NTG) without concurrent disease (Healthy-NTG), HCort and NTG (HCort-NTG), HCort and HTG (HCort-HTG), and iHTG. Lipoprotein fractions were assessed by lipoprotein electrophoresis and compared between groups. Fifty-one plasma samples were analyzed. Twenty-five dogs had NTG (16 Healthy-NTG, 9 HCort-NTG) and 26 dogs had HTG (7 iHTG, 19 HCort-HTG). Dogs with iHTG or HCort-HTG had significantly higher cholesterol concentrations than Healthy-NTG dogs. Dogs with HCort-HTG had higher cholesterol than HCort-NTG dogs. There was a significantly higher low-density lipoprotein (LDL) percentage in iHTG and HCort-HTG dogs than HCort-NTG dogs. HCort-HTG dogs also had lower high-density lipoproteins (HDL) than HCort-NTG dogs. It was not possible to readily distinguish MSs with iHTG from MSs with HCort-HTG or Healthy-NTG using lipoprotein electrophoresis fractions. The diagnosis of iHTG remains a diagnosis by exclusion.

External validation of a United Kingdom primary-care Cushing's prediction tool in a population of referred Dutch dogs

BACKGROUND

A prediction tool was developed and internally validated to aid the diagnosis of Cushing's syndrome in dogs attending UK primary-care practices. External validation is an important part of model validation to assess model performance when used in different populations.

OBJECTIVES

To assess the original prediction model's transportability, applicability, and diagnostic performance in a secondary-care practice in the Netherlands.

ANIMALS

Two hundred thirty client-owned dogs.

METHODS

Retrospective observational study. Medical records of dogs under investigation of Cushing's syndrome between 2011 and 2020 were reviewed. Dogs diagnosed with Cushing's syndrome by the attending internists and fulfilling ALIVE criteria were defined as cases, others as non-cases. All dogs were scored using the aforementioned prediction tool. Dog characteristics and predictor-outcome effects in development and validation data sets were compared to assess model transportability. Calibration and discrimination were examined to assess model performance.

RESULTS

Eighty of 230 dogs were defined as cases. Significant differences in dog characteristics were found between UK primary-care and Dutch secondary-care populations. Not all predictors from the original model were confirmed to be significant predictors in the validation sample. The model systematically overestimated the probability of having Cushing's syndrome (a = -1.10, P < .001). Calibration slope was 1.35 and discrimination proved excellent (area under the receiver operating curve = 0.83).

CONCLUSIONS AND CLINICAL IMPORTANCE

The prediction model had moderate transportability, excellent discriminatory ability, and overall overestimated probability of having Cushing's syndrome. This study confirms its utility, though emphasizes that ongoing validation efforts of disease prediction tools are a worthwhile effort.

Serum Bile Acids Concentrations and Liver Enzyme Activities after Low-Dose Trilostane in Dogs with Hyperadrenocorticism

Hyperadrenocorticism (HAC) often leads to vacuolar hepatopathy. The impact of trilostane treatment on serum total bile acids (SBAs) concentrations in dogs with HAC remains unknown. This study investigated SBAs concentrations in healthy dogs and those with HAC following trilostane therapy. Ten healthy dogs and fifteen dogs with HAC were prospectively enrolled. A biochemistry profile and pre- and post-prandial SBAs concentrations were determined in each dog. Dogs with HAC were reassessed at 1 and 3 months after the initiation of trilostane treatment. Dogs with HAC had significantly higher serum ALT, ALP, and GGT activities, and cholesterol, triglyceride, and pre-prandial SBAs concentrations compared to healthy dogs. After 3 months of trilostane treatment, polyuria/polydipsia and polyphagia were completely resolved in 42.8% and 35.7%, respectively. Significant improvements in serum ALT and ALP activities and cholesterol concentrations were observed within 1-3 months of trilostane treatment. However, pre- and post-prandial SBAs concentrations did not significantly decrease. These findings suggest that treatment with low-dose trilostane for 3 months appears to reduce serum liver enzyme activities, but not SBAs concentrations. Further investigation is warranted to explore the effects of low-dose trilostane treatment on SBAs concentrations for a longer duration or after achieving appropriate post-ACTH cortisol levels.

Diagnostic cut-off values for the urinary corticoid:creatinine ratio for the diagnosis of canine Cushing's syndrome using an automated chemiluminescent assay

BACKGROUND

Cushing's syndrome is one of the most common endocrinopathies in dogs. The preferred screening test for spontaneous Cushing's syndrome is the low-dose dexamethasone suppression test (LDDST). The diagnostic value of urinary cortisol:creatinine ratios (UCCR) is questionable.

OBJECTIVES

The aim of this study was to determine diagnostic cut-off values for UCCR testing in comparison with LDDST as a clinical reference standard and to calculate the sensitivity and specificity.

METHODS

Data from 2018 to 2020 were obtained retrospectively from a commercial laboratory. Both LDDST and UCCR were measured by automated chemiluminescent immunoassay (CLIA). The maximum interval between both tests was 14 days. The optimal cut-off value for UCCR testing was calculated by the Youden index. The sensitivity and specificity of these cut-off values for the UCCR test and LDDST were assessed by Bayesian latent class models (BLCMs).

RESULTS

This study included 324 dogs with both UCCR test and LDDST results. The optimal UCCR cut-off value, calculated by the Youden index, was 47.4 × 10-6 . Any UCCR <40 × 10-6 was interpreted as a negative result, 40-60 × 10-6 as values in a gray zone, and >60 × 10-6 as positive. Using the cut-off of 60 × 10-6 , BLCM showed 91% (LDDST) and 86% (UCCR test) sensitivity and a specificity of 54% (LDDST) and 63% (UCCR test).

CONCLUSIONS

Considering an 86% sensitivity and a 63% specificity, UCCR testing may be considered a first-line investigation to rule out Cushing's syndrome using CLIA analysis. Urine samples can be collected noninvasively at home by the owner, reducing the potential impact of stress.

Utility of 1,2-o-dilauryl-rac-glycero glutaric acid-(6'-methylresorufin)-ester-lipase for monitoring dogs with chronic pancreatitis

BACKGROUND

The utility of 1,2-o-dilauryl-rac-glycero glutaric acid-(6'-methylresorufin)-ester-(DGGR)-lipase activity (DLA) in monitoring clinical progression of chronic pancreatitis (CP) in dogs is unknown.

OBJECTIVE

To examine the association of DLA with clinical signs of CP, as assessed by a CP clinical severity score (CPCSS).

ANIMALS

Twenty-four dogs.

METHODS

This is a retrospective study. Chronic pancreatitis was diagnosed based on clinical signs and DLA > 250 U/L and monitored using CPCSS and DLA.

RESULTS

The study included 134 visits (median, 10 visits/dog; range, 2-11). Mild-moderate (CPCSS, 0-3) and severe (CPCSS, ≥4) disease were documented in 94 (70%) and 40 (30%) visits, respectively. In emergency visits (n = 44; 33%) CPCSS (median, 5; range, 0-15) and DLA (median, 534 U/L; range, 63-7133) were higher (P < .001 and P = .003, respectively) than in scheduled ones (n = 90; 67%; median, 1; range, 0-6 and median, 384 U/L; range, 49-3747, respectively). DGGR-lipase activity was associated (P = .009) with the CPCSS, with a lower activity documented in mild-moderate CPCSS (median 391 U/L; range, 49-3747), compared to severe score (median, 558 U/L; range, 63-7133). DGGR-lipase activity was significantly, but weakly, correlated with CPSS (r = 0.233, P = .007). DGGR-lipase activity inefficiently discriminated mild-moderate vs severe CP (area under the receiver operator characteristics curve, 0.64; 95% confidence interval, 0.53-0.75; P = .012), with DLA cutoff of 428 U/L corresponding to sensitivity of 65% and specificity of 63%.

CONCLUSIONS AND CLINICAL IMPORTANCE

Increased DLA is associated with emergency revisits in dogs with CP, possibly reflecting acute flare-ups. DGGR-lipase activity was associated with the CPCSS over the follow-ups but could not differentiate disease severity.

QT interval instability and variability in dogs with naturally-occurring hypercortisolism

Hypercortisolism is one of the most common endocrine diseases in dogs. In humans, it is clearly associated with a higher risk of cardiovascular events, but studies in dogs are scarce. To investigate the arrhythmogenic risk of dogs with naturally-occurring hypercortisolism (NOHC), indices of variability and instability of the QT interval were retrospectively studied in 38 dogs with NOHC and prospectively studied in 12 healthy dogs: variance (QTv), total instability (TI), short-term (STI) and long-term (LTI), and mean (QTm). Except for QTm, all parameters studied were higher in the NOHC group than in the control group. In addition, STI and QTv showed moderate positive correlation with left ventricle wall thickness. The NOHC group was subdivided according to cortisol suppression pattern in the low-dose dexamethasone suppression test. All electrocardiographic indices of partial and absent suppression patterns were numerically higher than healthy dogs. QTv and TI were lower in the control group than in both NOHC subgroups. LTI and STI were lower in the CG than in the group with the partial suppression pattern. There was no statistical difference between sex groups in any of the electrocardiographic parameters studied. This result might indicate that the etiology of NOHC, and its consequent influence on hypothalamus-pituitary-adrenal axis could interfere on the heterogeneity of ventricular repolarization parameters in different ways, especially in the short-term and the long-term stability; however further studies are necessary to understand the role of cortisol on electrical instability in dogs.

Re-evaluation of the low-dose dexamethasone suppression test in dogs

OBJECTIVES

This study aims to re-evaluate the low-dose dexamethasone suppression test 8-hour cortisol cut-point for the diagnosis of hypercortisolism in dogs using a solid-phase, competitive chemiluminescent enzyme immunoassay.

MATERIALS AND METHODS

Twenty-seven client-owned dogs with naturally occurring hypercortisolism and 30 healthy control dogs were prospectively recruited. Performance of the low-dose dexamethasone suppression test was assessed using sensitivity, specificity and a receiver operating characteristic curve compared to a clinical diagnosis of hypercortisolism including response to treatment.

RESULTS

Twenty-four dogs were diagnosed with pituitary-dependent hypercortisolism and three with adrenal-dependent hypercortisolism. In 30 healthy control dogs, 8-hour post-dexamethasone cortisol concentrations ranged from 5.5 to 39 nmol/L. A receiver operating characteristic curve curve constructed from the 8-hour post-dexamethasone cortisol concentrations of hypercortisolism and control dogs demonstrated that the most discriminatory cut-point was more than 39 nmol/L with sensitivity of 85.2% (95% confidence interval, 67.5% to 94.1%) and specificity of 100% (95% confidence interval, 88.7% to 100.0%) and an area under the curve of 0.963.

CLINICAL SIGNIFICANCE

The optimal cut-point of more than 36 nmol/L proposed by this study is similar to the currently accepted 8-hour cortisol concentration cut-point for diagnosing hypercortisolism when using a solid-phase, competitive chemiluminescent enzyme immunoassay.

Inverse relationship between eosinophil profiles and serum glucose concentration in dogs with naturally occurring hypercortisolism

Hyperglycemia and eosinopenia are well-known characteristics of hypercortisolism (HC) in humans, however, their association in dogs with HC has rarely been reported. This study aimed to evaluate the association between eosinophils and serum fasting glucose concentration in dogs with HC. Forty-seven dogs with HC and 43 dogs with non-adrenal illness were included. In this retrospective cohort study, the complete blood count, blood chemistry profile, and pre- and post-adrenocorticotropic hormone (ACTH) cortisol concentrations were analyzed. Significant differences were found in neutrophil, monocyte, eosinophil, and platelet counts; eosinophil percentage; neutrophil-to-lymphocyte ratio; aspartate aminotransferase, alanine aminotransferase, and gamma-glutamyl transferase activities (P < 0.05) between the groups. In dogs with HC, the eosinophil percentage was inversely correlated with fasting blood glucose (r = -0.3515, P = 0.0154) and post-ACTH cortisol concentrations (r = -0.6509, P < 0.0001). The neutrophil-to-lymphocyte ratio was inversely correlated with the eosinophil percentage (r = -0.4573, P = 0.0012) and count (r = -0.3688, P = 0.0108), but positively correlated with the fasting blood glucose level (r = 0.3888, P = 0.0069). Such correlations were not identified in dogs with non-adrenal illness. A multivariate analysis showed that only eosinophil percentage was associated with the presence of hyperglycemia in dogs with HC (odds ratio = 2.100, 95% confidence interval = 1.051-4.199, P = 0.0360). Therefore, eosinopenia induced by excess cortisol might be associated with altered glucose metabolism in dogs with HC. A better understanding of this correlation could be valuable to predict and prevent the complications of HC.

Frequency and risk factors for naturally occurring Cushing's syndrome in dogs attending UK primary-care practices

Objectives

To estimate the frequency and risk factors for Cushing's syndrome in dogs under UK primary veterinary care.

Materials and Methods

Dogs with Cushing's syndrome were identified by searching electronic patient records of primary‐care veterinary practices. Pre‐existing and incident cases of Cushing's syndrome during 2016 were included to estimate the 1‐year period prevalence. Incident cases were used to estimate the annual incidence and to identify demographic risk factors for the diagnosis of Cushing's syndrome in dogs, through multivariable logistic regression.

Results

Analysis included 970 pre‐existing and 557 incident cases of Cushing's syndrome from a population of 905,544 dogs. The estimated 1‐year period prevalence for Cushing's syndrome in dogs under veterinary care was 0.17% (95% confidence interval 0.16 to 0.18) and incidence was 0.06% (95% confidence interval 0.05 to 0.07). In multivariable logistic regression modelling, the Bichon frise (odds ratio=6.17, 95% confidence interval 4.22 to 9.00), Border terrier (5.40, 95% confidence interval 3.66 to 7.97) and Miniature schnauzer (3.05, 95% confidence interval 1.67 to 5.57) had the highest odds of Cushing's syndrome. The Golden retriever (0.24, 95% confidence interval 0.06 to 0.98) and Labrador retriever (0.30, 95% confidence interval 0.17 to 0.54) were the most protected breeds. Increasing age, bodyweight greater than the breed‐sex mean and being insured also showed increased odds of Cushing's syndrome.

Clinical Significance

As Cushing's syndrome is predominately diagnosed and managed in primary‐care practice, this study provides valuable new information of its epidemiology in this setting. Demographics reported are supportive of previous work and additional novel associations identified, such as the Border terrier, could enhance the index of suspicion for veterinarians.

Validation study of canine serum cortisol measurement with the Immulite 2000 Xpi cortisol immunoassay

We report the results of validation of canine serum cortisol determination with the Immulite 2000 Xpi cortisol immunoassay (Siemens), with characterization of precision (CV), accuracy (spiking-recovery [SR] bias), and observed total error (TEo = bias + 2CV) across the reportable range, specifically at the most common interpretation thresholds for dynamic testing. Imprecision increased at increasing rate with decreasing serum cortisol concentration and bias was low, resulting in increasing TEo with decreasing serum cortisol concentration. Inter-laboratory comparison study allowed for determination of range-based bias (RB) and average bias (AB). At 38.6 and 552 nmol/L (1.4 and 20 μg/dL), between-run CV was 10% and 7.5%, respectively, and TEo ~30% and ~20%, respectively (TEo remained similar regardless of the considered bias: SR, RB, or AB). These analytical performance parameters should be considered in the interpretation of results and for future expert consensus discussions to determine recommendations for allowable total error (TEa). Importantly, the commonly used thresholds for interpretation of results were determined ~40 y ago with different methods of measurements and computation, hence updating is desirable. Quality control material (QCM) had between-run imprecision of 4% for QCM1 and 7% for QCM2; the bias was minimal for both levels. Acceptable QC rules are heavily dependent on the desired TEa for the QCM system (TEaQCM), itself limited by the desired clinical TEa. At low TEaQCM (20-33%), almost no rules were acceptable, whereas at high TEaQCM (50%), almost all rules were acceptable; further investigation is needed to determine which TEaQCM can be guaranteed by simple QC rules.

Adrenal cortex stimulation with hCG in spayed female dogs with Cushing's syndrome: Is the LH-dependent variant possible?

Background:

The expression and overexpression of luteinizing hormone (LH) receptors in the canine adrenal gland cortex have been reported. Therefore, it was hypothesized that a LH-dependent form of Cushing’s syndrome (CS) could exist in dogs.

Aim:

To assess whether the adrenal gland post-ovariectomy (OVx) exhibits a greater response to adrenocorticotrophin (ACTH) stimulation; to evaluate whether the adrenal gland responds to human chorionic gonadotropin (hCG) stimulation by increasing the release of cortisol; and to consider whether hCG stimulus testing would be useful as a diagnosis for possible cases of LH-dependent CS.

Methods:

Cortisol concentrations were measured from healthy female dogs (n=16) at baseline and following ACTH stimulation before and 2 months after gonadectomy (OVx). Cortisol concentrations were also measured for female dogs with CS (n = 14) following administration of hCG (5000 IU). A post-hCG cortisol concentration greater than 140 nmol/l was used to define dogs with LH-dependent Cushing’s syndrome.

Results:

In normal female dogs, both pre- and post-stimulation cortisol concentrations increased following OVx (p = 0.002 and p = 0.0003, respectively). In female dogs with CS, cortisol concentrations increased following stimulation with hCG in 57% (8/14; p = 0.002). Age at the time of OVx was associated (p = 0.015) with the cortisol response to hCG [8 (5–9) years vs. 3.5 (2–6) years, p = 0.0013).

Conclusion:

Based on these results, an LH-dependent form of CS occurs in spayed female dogs, and that it is more likely to occur when female dogs are spayed later in life.

Retrospective study evaluation of DGGR lipase for diagnosis, agreement with pancreatic lipase and prognosis in dogs with suspected acute pancreatitis

OBJECTIVES

Activity of 1,2-o-dilauryl-rac-glycero-3-glutaric acid-(6'-methylresorufin) ester (DGGR) lipase is considered to be more pancreas specific than traditional lipase assays. The aim of this study was to evaluate the diagnostic performance of DGGR lipase activity for suspected acute pancreatitis in dogs and to assess its prognostic usefulness.

METHODS

Retrospective study of case records for suspected acute pancreatitis based on clinician-stated diagnosis, point-of-care and quantitative canine pancreas-specific lipase (cPL) results and consistent ultrasonographic features. Diagnostic performance of DGGR lipase was assessed by receiver-operating characteristic curve analysis, agreement by Cohen's kappa (κ) and prognostic value by multiple regression analysis.

RESULTS

Median DGGR lipase activity was significantly (P < 0.001) higher in dogs with suspected acute pancreatitis [93.7 (range, 11.0-2853.0) U/L (n = 158)] compared to those with no evidence of pancreatitis [range, 20.9 (6.7-89.0) U/L (n = 356)]. A DGGR lipase activity >42.15 U/L had the best combined diagnostic sensitivity (81.0%) and specificity (92.1%). Previously established cut-offs (>130 and >80 U/L) had sensitivities of 40.5 and 43.0%, and specificities of 100 and 99.7%, respectively. There was near perfect (κ = 0.821) and substantial (κ = 0.751) agreement between DGGR lipase activity >42.15 U/L and quantitative cPL concentrations ≥200 and ≥400 μg/L, respectively. DGGR lipase activity but not quantitative cPL concentration was statistically (P = 0.043, odds ratio = 0.999) predictive of discharge but clinical utility is questionable.

CLINICAL SIGNIFICANCE

Using DGGR lipase at the lower cut-off could provide an additional test for supporting a diagnosis of acute pancreatitis in dogs particularly if cPL results are not available. Larger studies are required to more fully assess its value in prognostication.

Rational use of diagnostic and screening tests

Veterinarians have a vast and ever-expanding array of diagnostic tests available to them. However, this abundance can be an embarrassment of riches that confounds diagnosis and undermines patient care if we do not make critical and informed decisions about the selection and interpretation of the tests we employ. Effective use of diagnostic tests requires a deliberate and informed approach. We must consider the strengths and weaknesses of the tests themselves and the clinical context, and we must be wary of the many biases that skew our use and interpretation of diagnostic tests. Understanding sensitivity and specificity, likelihood, prevalence and predictive value, the basic principles of Bayesian reasoning, and the cognitive biases that drive inappropriate testing are all critical to ensuring our use of imaging and laboratory testing improves patient outcomes.

Evaluation of 1,2-O-dilauryl-rac-glycero glutaric acid-(6'-methylresorufin) ester (DGGR) and 1,2-diglyceride lipase assays in dogs with naturally occurring hypercortisolism

1,2-O-dilauryl-rac-glycero glutaric acid-(6'-methylresorufin) ester (DGGR) lipase activity has been proposed as a faster and less expensive test used in the diagnosis of acute pancreatitis (AP) compared to canine pancreatic lipase immunoreactivity (cPLI), which is considered the most sensitive and specific serum test available for dogs. Elevations in lipase activity have been observed in dogs with naturally occurring hypercortisolism (HC) and in those treated with exogenous steroids, which complicates the diagnosis of AP in dogs with HC. We compared lipase activity measured by DGGR and 1,2-diglyceride (1,2-DiG) assays in 22 dogs with HC, 22 with AP, and 22 healthy dogs. The dogs with HC had no clinical signs or ultrasonographic findings consistent with AP. DGGR lipase activity was elevated in 64% and 73% of the dogs with HC and AP, respectively, and in 18% of healthy dogs. 1,2-DiG lipase activity was high in 23% and 36% of the dogs with HC and AP, respectively, and in 5% of the healthy dogs. Both DGGR and 1,2-DiG lipase activities were significantly different between the healthy dogs and the other 2 groups, whereas no differences were detected between the dogs with HC and those with AP. Our results support a lack of specificity for both DGGR and 1,2-DiG lipase activity assays in aiding the diagnosis of AP in dogs with HC.

Machine-learning based prediction of Cushing's syndrome in dogs attending UK primary-care veterinary practice

Cushing’s syndrome is an endocrine disease in dogs that negatively impacts upon the quality-of-life of affected animals. Cushing’s syndrome can be a challenging diagnosis to confirm, therefore new methods to aid diagnosis are warranted. Four machine-learning algorithms were applied to predict a future diagnosis of Cushing's syndrome, using structured clinical data from the VetCompass programme in the UK. Dogs suspected of having Cushing's syndrome were included in the analysis and classified based on their final reported diagnosis within their clinical records. Demographic and clinical features available at the point of first suspicion by the attending veterinarian were included within the models. The machine-learning methods were able to classify the recorded Cushing’s syndrome diagnoses, with good predictive performance. The LASSO penalised regression model indicated the best overall performance when applied to the test set with an AUROC = 0.85 (95% CI 0.80–0.89), sensitivity = 0.71, specificity = 0.82, PPV = 0.75 and NPV = 0.78. The findings of our study indicate that machine-learning methods could predict the future diagnosis of a practicing veterinarian. New approaches using these methods could support clinical decision-making and contribute to improved diagnosis of Cushing’s syndrome in dogs.

Patterns of the low-dose dexamethasone suppression test in canine hyperadrenocorticism revisited

BACKGROUND

The low-dose dexamethasone suppression test (LDDT) is considered an accurate screening and valuable differentiation test in dogs with suspected hyperadrenocorticism (HAC). A recent study showed that the different response patterns not only provide complementary information about etiology, but also the probability of HAC in these patients.

OBJECTIVES

We aimed to determine the diagnostic test performance of LDDT response patterns in a population of dogs from an animal hospital.

METHODS

The electronic database was retrospectively searched for dogs suspected of HAC that were given an LDDT. Dogs with acute non-adrenal illnesses during the test were excluded. Response patterns were classified as complete suppression, lack of suppression, partial suppression, escape, inverse, and increasing patterns. Cortisol concentrations ≥ 27.59 nmol/L (≥1 µg/dL) 8 hours after dexamethasone administration were considered positive results irrespective of the patterns observed. Calculations included likelihood ratios (LRs) and predictive values (PVs).

RESULTS

HAC and non-adrenal illness were diagnosed in 115 (54%) and 62 (46%) dogs, respectively. The positive (+) LRs (95% CI) for the lack of suppression, partial suppression, escape, and an inverse pattern to diagnose HAC were infinite, 8.09 (2-32.72), 3.23 (0.75-14), and 0.2 (0.06-0.73), respectively.

CONCLUSIONS

The study confirms that the "lack of suppression" pattern strongly supports a diagnosis of HAC. It shows that the "partial suppression" pattern moderately increases, and the "inverse" pattern decreases the likelihood of HAC. The fact that the study found no association between the "escape" pattern and a diagnosis of HAC, does not support its integration into decision making.

Effect of prednisolone therapy on serum levels of 1,2-O-dilauryl-rac-glycero glutaric acid-(6'-methylresorufin) ester lipase in dogs

BACKGROUND

Activity of 1,2-O-dilauryl-rac-glycero glutaric acid-(6'-methylresorufin) ester (DGGR) lipase in serum shows good agreement with pancreatic lipase (cPL) in dogs. Although prednisolone therapy does not seem to affect serum cPL concentration, its influence on DGGR lipase is unclear.

OBJECTIVES

The aim of the study was to evaluate the effect of prednisolone therapy on DGGR lipase serum activity in dogs.

ANIMALS

Thirty-four dogs were used, of which 17 dogs received prednisolone (study group) and 17 healthy dogs did not receive treatment.

METHODS

A prospective cohort study measured DGGR lipase activity in both groups at 3 time points: T0, T1, and T2, corresponding to days 0, 7-10, and 21-30, respectively. Dogs from study group presented a medical reason that justified the use of prednisolone for at least 3 weeks. Initial prednisolone dose was .5-2.0 mg/kg/day PO with a reduction at T1 to a final dose that was maintained until T2. DGGR lipase activity >160 U/L was defined as clinically relevant.

RESULTS

In the study group, DGGR lipase activity increased significantly from T0 to T1 (P = .02) and decreased significantly from T1 to T2 (P = .02). Median DGGR activity at each time point (T0, T1, and T2) was 24.74 (14.45-31.48), 36.82 (23.8-80.16), and 29.52 (15.91-48.48) U/L, respectively. In the control group, no significant changes were observed over time (P = .93). The DGGR lipase activity and prednisolone doses were not correlated for both T0-T1 (r_s = .371, P = .14) and T1-T2 (r_s = 0.390, P = .12).

CONCLUSION AND CLINICAL IMPORTANCE

DGGR lipase activity was affected by prednisolone administered orally in dogs. However, this variation was not clinically important as values remained below the relevant upper limit.

Development and internal validation of a prediction tool to aid the diagnosis of Cushing's syndrome in dogs attending primary-care practice

BACKGROUND

Novel methods to aid identification of dogs with spontaneous Cushing's syndrome are warranted to optimize case selection for diagnostics, avoid unnecessary testing, and ultimately aid decision-making for veterinarians.

HYPOTHESIS/OBJECTIVES

To develop and internally validate a prediction tool for dogs receiving a diagnosis of Cushing's syndrome using primary-care electronic health records.

ANIMALS

Three hundred and ninety-eight dogs diagnosed with Cushing's syndrome and 541 noncase dogs, tested for but not diagnosed with Cushing's syndrome, from a cohort of 905 544 dogs attending VetCompass participating practices.

METHODS

A cross-sectional study design was performed. A prediction model was developed using multivariable binary logistic regression taking the demography, presenting clinical signs and some routine laboratory results into consideration. Predictive performance of each model was assessed and internally validated through bootstrap resampling. A novel clinical prediction tool was developed from the final model.

RESULTS

The final model included predictor variables sex, age, breed, polydipsia, vomiting, potbelly/hepatomegaly, alopecia, pruritus, alkaline phosphatase, and urine specific gravity. The model demonstrated good discrimination (area under the receiver operating curve [AUROC] = 0.78 [95% CI = 0.75-0.81]; optimism-adjusted AUROC = 0.76) and calibration (C-slope = 0.86). A tool was developed from the model which calculates the predicted likelihood of a dog having Cushing's syndrome from 0% (score = -13) to 96% (score = 10).

CONCLUSIONS AND CLINICAL IMPORTANCE

A tool to predict a diagnosis of Cushing's syndrome at the point of first suspicion in dogs was developed, with good predictive performance. This tool can be used in practice to support decision-making and increase confidence in diagnosis.

Diagnostic contribution of individual components of adrenal function tests to diagnose canine hyperadrenocorticism

There is limited information regarding the value of constitutive components of the ACTH stimulation test (ACTHST) and low-dose dexamethasone suppression test (LDDST) including serum baseline cortisol (BC), difference between post-ACTH stimulation cortisol (PC) and BC (ΔACTHC), cortisol concentration 4h after dexamethasone administration (4HC), difference between 4HC and BC (Δ4C), and the difference between cortisol concentration 8h after dexamethasone administration and 4HC (Δ8C). Therefore, the objective of this study was to determine if these components can predict hyperadrenocorticism, pituitary-dependent hyperadrenocorticism (PDH), or functional adrenocortical tumor (FAT) in dogs. Cortisol concentrations were normalized, as fold change (FC), to the PC reference interval upper limit. A total of 1267 dogs were included, with hyperadrenocorticism diagnosed in 537 (PDH, n=356; FAT, n=28; undetermined, n=153) and excluded in 730. The area under the receiver operating curves for BC, ΔACTHC, 4HC, Δ4C, and Δ8C to predict hyperadrenocorticism were 0.76 (95% confidence interval (CI), 0.73-0.79), 0.91 (95% CI, 0.89-0.93), 0.83 (95% CI, 0.80-0.87), 0.55 (95% CI, 0.50-0.60), and 0.67 (95% CI, 0.62-0.72), respectively. A diagnostic limit of ≥0.78 FC for ΔACTHC had excellent sensitivity (1.00; 95% CI, 0.74-1.00), but poor specificity (0.67; 95% CI, 0.64-0.71), to predict FAT in dogs with a positive ACTHST. A diagnostic limit of ≥-0.26 FC for Δ4C had excellent sensitivity (1.00; 95% CI, 0.79-1.00), but poor specificity (0.21; 95% CI, 0.18-0.26), to predict FAT in dogs with a positive LDDST. In hyperadrenocorticoid dogs that have positive ACTHST or LDDST results, ΔACTHC or Δ4C, respectively, could be used to exclude FAT.

A Preliminary Study of the Effect of Hyperadrenocorticism on Calcium and Phosphate Concentrations, Parathyroid Hormone and Markers of Bone Turnover in Dogs

Reports on the effects of hyperadrenocorticism (HAC) on bone turnover in dogs are largely confined to radiographic studies. The aim of this study was to more accurately assess bone turnover in dogs with HAC by measuring circulating total and ionized calcium and phosphate concentrations, both intact and whole parathyroid hormone (PTH) concentrations and markers of both osteoblastic (osteocalcin) and osteoclastic [carboxyterminal cross-linked telopeptide of type 1 collagen (ICTP) and urine aminoterminal telopeptide of type 1 collagen (NTX) activity]. Dogs with HAC and a control group were prospectively enrolled for comparison. Results from 49 dogs with HAC were compared with 39 dogs from a hospital control population. Plasma intact and whole PTH concentrations were determined using a human immunoradiometric assay. Serum osteocalcin and NTX concentrations were measured using human enzyme linked immunosorbent assays. Serum ICTP concentration was measured using a human radioimmunoassay. Total calcium concentrations in dogs with HAC (2.67 ± 0.25 mmol/L) were not significantly different than in the control group (2.67 ± 0.14 mmol/L). By contrast, phosphate concentrations were significantly (P = 0.0143) higher in dogs with HAC (1.46 ± 0.30 mmol/L) compared to the control group (1.28 ± 0.33 mmol/L). The median intact PTH concentration in HAC dogs was 9.25 (range, 1.34–95.45) pmol/L, which was significantly (P < 0.0001) higher than in the control group [median, 3.88 (range, 2.01–10.31) pmol/L]. Whole PTH concentrations were also significantly (P < 0.0001) higher in the HAC group [median, 4.61 (range, 0.56–125.16) pmol/L] compared to the control group [median, 1.83 (range, 0.88–6.81) pmol/L]. Serum osteocalcin and urine NTX concentrations were not significantly different between the two groups of dogs. The median ICTP concentration in dogs with HAC was 2.98 (range, 1.15–6.62) ng/mL which was significantly (P < 0.0001) lower than in the control dogs [median, 7.30 (range, 3.68–21.25) ng/mL]. Both whole and intact PTH concentrations are increased in dogs with HAC compared to a hospital control population. This does not however appear to be associated with a decrease in bone formation (as assessed by osteocalcin) or an increase in bone resorption (as assessed by ICTP and urine NTX).

Diagnosis of spontaneous hyperadrenocorticism in dogs. Part 2: Adrenal function testing and differentiating tests

Hyperadrenocorticism is a relatively common endocrine disorder in dogs that has been extensively described. However, its diagnosis remains challenging because there is no true reference standard test, and a myriad factors can affect the diagnostic performance of the commonly used adrenal function tests. Ultimately, the diagnosis is based on a combination of signalment, history and clinical findings, and a variety of diagnostic test results. The second part of this review aims to appraise available data on diagnostic performance of adrenal function tests in naturally occurring canine hyperadrenocorticism.

Diagnosis of spontaneous hyperadrenocorticism in dogs. Part 1: Pathophysiology, aetiology, clinical and clinicopathological features

Hyperadrenocorticism is a relatively common endocrine disorder in dogs. It occurs as a result of a functional pituitary or adrenal tumour, although other causes have been rarely reported. Canine hyperadrenocorticism has been extensively described but diagnosing this disease remains challenging. Few studies have investigated the clinical and clinicopathological features helpful in differentiating dogs with hyperadrenocorticism from dogs in which the disease is suspected but eventually excluded. Ultimately the diagnosis is based on a combination of multiple pieces of information emanating from the signalment, history, clinical findings, and a variety of diagnostic tests. The first part of this review aims to critically appraise the available data on epidemiology, clinical and laboratory features of naturally occurring canine hyperadrenocorticism.

The interpretive contribution of the baseline serum cortisol concentration of the ACTH stimulation test in the diagnosis of pituitary dependent hyperadrenocorticism in dogs

Background

Current recommendation for performing the ACTH stimulation test (ACTHST) for diagnosis of hyperadrenocorticism (HAC) advocates the collection of baseline serum cortisol concentration (BC), but no references for interpretation of its results exist.

Objective

Evaluate the contribution of BC of the ACTHST to the diagnosis of HAC.

Animals

Fifty‐four dogs were evaluated for suspected HAC at a referral hospital.

Methods

Records of dogs that had been evaluated by ACTHST for suspected HAC were reviewed. Receiver operator characteristics (ROC) analyses were used to assess the performance of BC, post‐stimulation serum cortisol concentrations (PC), post‐to‐baseline cortisol concentration difference (DeltaC) and quotient (RatioC) for the diagnosis of HAC by comparing the area under the ROC curve (AUC) of PC to each of the other tests.

Results

The AUC of PC (95% confidence interval [CI]: 0.92; 95% CI, 0.81‐0.98) was significantly higher than AUCs of BC (0.70; 95% CI, 0.56‐0.82; P = .01) and RatioC (0.55; 95% CI, 0.41‐0.69; P < .001), and was not significantly different from AUC of DeltaC (0.86; 95% CI, 0.74‐0.94; P = .09). An optimal cutoff value of 683 nmol/L (24.8 μg/dL) for PC yielded a sensitivity of 86% and a specificity of 94%, respectively, and a cutoff value of 718 nmol/L (26.0 μg/dL) yielded a specificity of 100% with of 81% sensitivity for the diagnosis of pituitary‐dependent HAC.

Conclusion and Clinical Importance

The PC had good discriminatory ability for the diagnosis of HAC. It was comparable to DeltaC, whereas BC and RatioC were ineffective. Current recommendations to collect samples for BC appear redundant.

Evaluation of individual low-dose dexamethasone suppression test patterns in naturally occurring hyperadrenocorticism in dogs

BACKGROUND

Dogs with hyperadrenocorticism (HAC) may be more mildly affected at the time of diagnosis today, which could influence the prevalence of associated clinical and clinicopathological abnormalities and diagnostic test performance. Different low-dose dexamethasone suppression test (LDDST) result patterns have not been evaluated individually.

OBJECTIVES

To assess the current features of HAC and evaluate if the diagnostic test performance of individual LDDST result patterns differ.

ANIMALS

One hundred and twenty-three dogs undergoing investigation for HAC.

METHODS

Retrospective evaluation of dogs in which a LDDST was performed and HAC confirmed or excluded by alternative means. Cases with basal cortisol concentrations (t0 ) < 1 μg/dL were excluded. Each LDDST result was classified as (a) complete suppression (t3 and t8  < 1 μg/dL), (b) lack of suppression (t3 and t8  > 1 μg/dL and both > 50% t0 ), (c) partial suppression (t3 and t8  > 1 μg/dL but either < 50% t0 ), (d) escape (t8  > 1 μg/dL and t3  < 1 μg/dL) or (e) inverse (t3  > 1 μg/dL and t8  < 1 μg/dL) pattern.

RESULTS

Fifty-nine (48%) dogs were diagnosed with HAC and 64 (52%) with non-adrenal illness. Hyperadrenocorticism cases had similar clinicopathological abnormalities compared to previous reports. Sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV) (95% confidence interval [CI]) of the LDDST for diagnosing HAC were 96.6 (91.9-100)%, 67.2 (55.7-78.7)%, 73.1 (63.2-82.9)%, and 95.6 (89.5-100)%, respectively. Lack of suppression pattern had the highest PPV (93.9 [85.8-100]%) followed by the partial suppression pattern (67.9 [50.6-85.2]%) and escape or inverse pattern (36.8 [15.1-58.5]%).

CONCLUSIONS AND CLINICAL IMPORTANCE

A lack of suppression LDDST pattern has the highest PPV for diagnosing HAC followed by a partial suppression pattern. By contrast, the escape or inverse pattern provided limited support of HAC.