Recent advances in the diagnosis of Cushing's syndrome in dogs

Urinary steroid profiling using liquid chromatography-tandem mass spectrometry for the diagnosis of canine Cushing's syndrome

Serum cortisol measurements by chemiluminescence enzyme immunoassay (CLEIA) are widely used to diagnose hypercortisolism (HC) or Cushing's syndrome in dogs. However, they are associated with problems such as the need for multiple blood collections under stressful conditions or cross-reactivity between hormones. Therefore, a less invasive and more accurate diagnostic method is required. This study aimed to develop a urinary steroid profile analysis method using liquid chromatography-tandem mass spectrometry (LC/MS/MS) and to evaluate its clinical usefulness. Sixty-five healthy dogs and 38 dogs with suspected HC were included in the study. Using LC/MS/MS, the levels of 11 steroid hormones in the urine were determined. We established the upper limit of the reference interval for each urinary steroid-to-creatinine ratio and evaluated their diagnostic performances. The levels of the five steroid hormones were significantly higher in the 14 dogs with HC than in the 24 dogs with mimicking HC and 65 healthy dogs. The urinary corticosterone-to-creatinine ratio showed the highest diagnostic accuracy (area under the curve, 0.96). A significant correlation was seen between urinary cortisol concentrations measured by LC/MS/MS and CLEIA (rs = 0.88, P <0.001), although the CLEIA measurements were significantly higher than the LC/MS/MS measurements (P <0.001). LC/MS/MS-based urinary steroid profiles are a promising tool for diagnosing canine HC.

Canine noninflammatory alopecia: An approach to its classification and a diagnostic aid

Noninflammatory alopecia is common in dogs and is a frequent cause to consult a veterinarian. It is also a common reason to take biopsies. Noninflammatory alopecia can be attributed to a decreased formation or cytodifferentiation of the hair follicle or the hair shaft in utero, resulting in congenital alopecia. Congenital alopecia often has a hereditary cause, and examples of such disorders are ectodermal dysplasias associated with gene variants of the ectodysplasin A gene. Noninflammatory alopecia may also be caused by impaired postnatal regeneration of hair follicles or shafts. Such disorders may have a clear breed predilection, and alopecia starts early in life. A hereditary background is suspected in those cases but has not been proven. They are referred to as follicular dysplasia although some of these disorders present histologically like a hair cycle disturbance. Late-onset alopecia is usually acquired and may be associated with endocrinopathies. Other possible causes are impaired vascular perfusion or stress. As the hair follicle has limited possible responses to altered regulation, and histopathology may change during the course of a disease, a detailed clinical history, thorough clinical examination including blood work, appropriate biopsy site selection, and detailed histological findings need to be combined to achieve a final diagnosis. This review aims to provide an overview about the known noninflammatory alopecic disorders in dogs. As the pathogenesis of most disorders is unknown, some statements are based on comparative aspects or reflect the authors' opinion.

Increases in serum carbonylated protein levels of dogs with hypercortisolism

Protein carbonylation is an irreversible and degenerative modification that can be used to evaluate oxidative stress caused by glucocorticoids. In this study, we focused on protein carbonylation in dogs with hypercortisolism (HC). Sera samples were collected from 14 dogs diagnosed with HC and treated with trilostane, 12 dogs with inflammatory diseases (disease control group), and eight clinically healthy dogs. When the carbonylated protein levels were detected by the immunoblot analysis, one band of approximately 40 kDa was predominantly increased in the dogs with HC. The band was identified as haptoglobin using the liquid chromatography tandem mass spectrometry method. Furthermore, haptoglobin immune reactivity was higher in the dogs with HC. Although the average protein carbonylation level of the HC group was not significantly different from that of the other groups, the carbonylation level was significantly higher for the poorly controlled HC cases than for the well-controlled HC group. Additionally, the primary culture of canine hepatocytes was used to clarify the direct effect of glucocorticoids on protein carbonylation in dog livers. Both the carbonylated protein and haptoglobin clearly increased after 72 h. These findings suggest that haptoglobin and its carbonylated form are increased with canine HC, and that the protein carbonylation ratio and/or haptoglobin level could be related to disease management. These factors could be useful as biomarkers for an oxidative stress reaction, at least in the liver, and for treatment monitoring of HC.

Localized alopecia and suppression of hypothalamic-pituitary-adrenal (HPA) axis in dogs following treatment with difluprednate 0.05% ophthalmic emulsion (Durezol®)

Background

Despite the common use of topical ophthalmic corticosteroids in dogs, detailed reports on systemic and dermatologic adverse effects are limited.

Results

Nine purpose-bred research Beagles were treated with difluprednate 0.05% ophthalmic emulsion in one or both eyes 2–3 times daily. Some difluprednate treated dogs developed mild to severe alopecia of the periocular region, face, and distal pinna (5/9). The median duration of treatment prior to onset of dermatologic signs for difluprednate treated dogs was 550 days (453–1160 days). Diagnostic testing included complete blood count (CBC) and serum biochemistry, adrenocorticotropic hormone (ACTH) stimulation testing combined with endogenous ACTH measurement, and skin biopsy. The CBC and chemistry were within normal limits for all dogs. There were varying degrees of suppression of the hypothalamic-pituitary-adrenocortical (HPA) axis with difluprednate treatment. Dogs with the most profound alopecic changes had less pronounced HPA axis suppression compared to dogs with no integumentary changes. Skin biopsies demonstrated follicular atrophy and follicular keratosis. When topical difluprednate was reduced to unilateral therapy, the hair regrew on the untreated side of the face. In addition to the affected research dogs, a 7-year old female spayed Chihuahua that was being treated as a clinical patient with long-term difluprednate 0.05% ophthalmic emulsion developed generalized hypotrichosis on the head and body and a potbellied appearance. ACTH stimulation testing revealed suppression of the HPA axis with a mild increase in serum alkaline phosphatase (ALP) activity and a urine specific gravity of 1.016. The combination of clinical signs and laboratory abnormalities was supportive of iatrogenic hyperadrenocorticism.

Conclusions

In dogs long-term use of difluprednate ophthalmic emulsion results in HPA axis suppression and in some cases iatrogenic hyperadrenocorticism. A novel pattern of localized alopecia is suspected to be related to dermal absorption and local action due to superior potency and penetration compared to other commonly utilized ophthalmic corticosteroids.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12917-021-03072-9.

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.

A case of chronic lymphocytic leukemia masked by Cushing's disease in a dog

A 12-year-old, 3.5-kg, intact female dog was presented with polyuria, polydipsia, and a pendulous abdomen. Laboratory examinations showed elevated hepatobiliary enzyme levels and neutrophilic leukocytosis. The adrenocorticotropic hormone stimulation test confirmed hyperadrenocorticism (HAC). Trilostane therapy managed the clinical condition and cortisol concentration. However, lymphocytosis and nonregenerative anemia developed after HAC remission. Bone marrow aspiration analysis revealed a lymphoproliferative disorder with a clonal T-cell population. Accordingly, the patient was diagnosed with T-cell chronic lymphocytic leukemia (CLL) and concurrent HAC. Thereafter, chemotherapy was initiated, which improved the lymphocytosis. However, euthanasia was performed because of worsening quality of life at 45 weeks after the first presentation. These results suggested that CLL could be masked by excessive endogenous cortisol and discovered after HAC remission.

Increased longevity due to sexual activity in mole-rats is associated with transcriptional changes in the HPA stress axis

Sexual activity and/or reproduction are associated with a doubling of life expectancy in the long-lived rodent genus Fukomys. To investigate the molecular mechanisms underlying this phenomenon, we analyzed 636 RNA-seq samples across 15 tissues. This analysis suggests that changes in the regulation of the hypothalamic–pituitary–adrenal stress axis play a key role regarding the extended life expectancy of reproductive vs. non-reproductive mole-rats. This is substantiated by a corpus of independent evidence. In accordance with previous studies, the up-regulation of the proteasome and so-called ‘anti-aging molecules’, for example, dehydroepiandrosterone, is linked with enhanced lifespan. On the other hand, several of our results are not consistent with knowledge about aging of short-lived model organisms. For example, we found the up-regulation of the insulin-like growth factor 1/growth hormone axis and several other anabolic processes to be compatible with a considerable lifespan prolongation. These contradictions question the extent to which findings from short-lived species can be transferred to longer-lived ones.

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.

TRH-induced secretion of adrenocorticotropin and cortisol in dogs with pituitary-dependent hypercortisolism

Background: In dogs, spontaneous Cushing’s syndrome is most often pituitary-dependent and caused by hypersecretion of adrenocorticotropic hormone (ACTH), resulting in increased adrenocortical glucocorticoid secretion similar to horses. In horses with Cushing’s syndrome (or pituitary pars intermedia dysfunction [PPID]) a thyrotropin-releasing hormone (TRH) stimulation test can be used for diagnosis, as TRH administration results in increased circulating ACTH and cortisol concentrations in affected horses.

Objective: The aim of this study was to investigate the effect of TRH administration on the circulating ACTH and cortisol concentrations in dogs with pituitary-dependent hypercortisolism (PDH).

Methods: Ten clinically normal control dogs and 10 dogs with PDH, all client owned, underwent a TRH stimulation test with measurement of plasma concentrations of ACTH and cortisol, before and after intravenous administration of 10 μg TRH/kg bodyweight.

Results: Plasma ACTH concentration did not rise significantly after TRH stimulation, neither in PDH dogs nor in clinically normal dogs. In contrast, the plasma cortisol concentration did increase significantly after TRH stimulation in both groups (p = .003 in PDH and p < .001 in control). Immunohistochemistry of normal adrenal glands demonstrated the presence of TRH receptors in the whole adrenal cortex.

Conclusions: The results of this study demonstrate that the TRH stimulation test should be rejected as a tool to diagnose PDH in dogs. The observed TRH-induced increase in plasma cortisol concentration without a significant rise in plasma ACTH concentration may be explained by a direct effect of TRH on adrenocortical cells mediated by adrenocortical TRH receptors.

Treating canine Cushing's syndrome: Current options and future prospects

Naturally occurring hypercortisolism, also known as Cushing's syndrome, is a common endocrine disorder in dogs that can be caused by an adenocorticotrophic hormone (ACTH)-producing pituitary adenoma (pituitary-dependent hypercortisolism, PDH; 80-85% of cases), or by an adrenocortical tumor (ACT; 15-20% of cases). To determine the optimal treatment strategy, differentiating between these two main causes is essential. Good treatment options are surgical removal of the causal tumor, i.e. hypophysectomy for PDH and adrenalectomy for an ACT, or radiotherapy in cases with PDH. Because these options are not without risks, not widely available and not suitable for every patient, pharmacotherapy is often used. In cases with PDH, the steroidogenesis inhibitor trilostane is most often used. In cases with an ACT, either trilostane or the adrenocorticolytic drug mitotane can be used. Although mostly effective, both treatments have disadvantages. This review discusses the current treatment options for canine hypercortisolism, and considers their mechanism of action, efficacy, adverse effects, and effect on survival. In addition, developments in both adrenal-targeting and pituitary-targeting drugs that have the potential to become future treatment options are discussed, as a more selective and preferably also tumor-targeted approach could have many advantages for both PDH and ACTs.

Metformin reduces insulin resistance and the tendency toward hyperglycaemia and dyslipidaemia in dogs with hyperadrenocorticism

Hypercortisolism induces a state of insulin resistance that can occur concurrently with fasting hyperglycaemia, dyslipidaemia and diabetes mellitus. Metformin reduces hepatic glucose production and insulin resistance of the skeletal muscle and adipose tissue. The aim of this study was to evaluate the effects of metformin on the control of metabolic disorders of dogs with hyperadrenocorticism (HAC). Twenty-three dogs with HAC were randomly divided into two groups, consisting of a control group and a metformin group (10 mg metformin/kg/12 h). Both groups received the same treatment for HAC. At baseline and 3 months, blood glucose, total cholesterol, triglycerides and insulin concentrations, in addition to urinary cortisol:creatinine ratio, Homeostatic Model Assessment (HOMA) for insulin sensitivity and β-cell function were measured. Dogs treated with metformin showed significantly reduced glycaemia, cholesterolaemia and triglyceridaemia. They also presented reduced hyperinsulinism and insulin resistance, as well as improved pancreatic β-cell function. The implementation of metformin as an adjuvant therapy is effective for the normalisation of metabolic disorders of dogs with HAC.

Decrease of nitric oxide and increase in diastolic blood pressure are two events that affect renal function in dogs with pituitary dependent hyperadrenocorticism

Hyperadrenocorticism is a frequent disease in dogs. The excess of circulating cortisol affects different organs and metabolic pathways, producing severe adverse effects that endanger the animal’s life. Among these effects, hypertension and renal damage can be mentioned. A group of 20 dogs with pituitary dependent hyperadrenocorticism (PDH) and 12 control dogs were used to study the following parameters: cortisol and nitric oxide (NO nit/nit) concentrations, diastolic and systolic blood pressure, renal artery resistance index by Doppler ultrasound, the rate of glomerular filtration by radio-renogram excretion and the presence of proteins in urine. Dogs with PDH showed a significantly lower NO nit/nit (P<0.0001) than the controls and this correlated with high values of diastolic and systolic pressure (r = -0.87; P<0.0001 and r = -0.81; P<0.0001 respectively). Most dogs (80%) are hypertensive mainly due to an increase in diastolic pressure, which correlated positively with the UPC (r = 0.8; P<0.001) and negatively with the glomerular rate of filtration (r = -0.58; P=0.007). Systolic pressure only increased in 60% of the cases and did not correlate with the mentioned variables. In PDH the decrease of NO affects blood pressure. The diastolic pressure would seem to have the greatest impact on the kidneys, therefore its evaluation and control are important to avoid and/or control renal damage.

Concurrent hyperadrenocorticism and diabetes mellitus in dogs

Hyperadrenocorticism (HAC) and diabetes mellitus (DM) are two diseases that can occur concurrently in dogs. The objective of this study was to evaluate the coexistence of HAC and DM, and the risk factors involved that could contribute to the development of DM in dogs with HAC. A total of 235 dogs with HAC were studied and, according to their fasting glycemia, they were divided into three groups: <5.6mmol/L, between 5.6 and 10.08mmol/L and >10.08mmol/L. The following parameters were evaluated: age, gender, cause of HAC, body condition, glycemia, total cholesterol, triglycerides, urinary cortisol:creatinin ratio (UCCR) and survival time. A 13.61% concurrence of HAC and DM was observed. Dogs with a fasting glycemia >5.6mmol/L, with dislipemia, with Pituitary-Dependent Hyperadrenocorticism, UCCR >100×10^-6 and non-castrated females showed a higher risk of developing DM. The development of DM in dogs with HAC reduces the survival time.

Dynamic computed tomography of the pituitary gland using a single slice scanner in dogs with pituitary-dependent hypercortisolism

Selective removal of the pituitary adenoma has not been advocated in dogs with pituitary-dependent hypercortisolism because the pituitary adenoma is usually not visualized on routine computed tomography (CT). Dynamic pituitary CT scanning is aimed at the detection of the pituitary flush and, indirectly, at the presence and position of the adenoma. The first aim of this retrospective study was to compare findings of a multiple slice dynamic scanning protocol with those of a single slice dynamic protocol using a single slice CT scanner. The second aim was to compare the CT findings with surgical findings, and surgical findings with histopathological findings. Computed tomography with single and multiple slice dynamic scanning protocols was performed in 86 dogs with pituitary-dependent hypercortisolism. Thirty dogs underwent transsphenoidal hypophysectomy and pituitary specimens were collected as tumor, normal, mixed and neurohypophyseal samples and processed for histology. The pituitary flush was not detected more frequent in multiple slice dynamic scanning series than in single slice dynamic scanning series. However, in non-enlarged pituitaries, the flush was seen significantly more frequently than in enlarged pituitaries. Prediction of the nature of the tissue during hypophysectomy by the surgeon was inconclusive. In conclusion, when using a single slice CT scanner, both single or multiple slice dynamic scanning protocols can be used for localization of the neurohypophyseal flush, and, indirectly, the adenoma. However, based on this study, the aim of surgery in dogs with pituitary-dependent hypercortisolism remains total adenohypophysectomy, and when the neurophypophysis is recognized, it may be left in situ.

Autoantibodies against Cytochrome P450 Side-Chain Cleavage Enzyme in Dogs (Canis lupus familiaris) Affected with Hypoadrenocorticism (Addison's Disease)

Canine hypoadrenocorticism likely arises from immune-mediated destruction of adrenocortical tissue, leading to glucocorticoid and mineralocorticoid deficiency. In humans with autoimmune Addison's disease (AAD) or autoimmune polyendocrine syndrome (APS), circulating autoantibodies have been demonstrated against enzymes associated with adrenal steroid synthesis. The current study investigates autoantibodies against steroid synthesis enzymes in dogs with spontaneous hypoadrenocorticism. Coding regions of canine CYP21A2 (21-hydroxylase; 21-OH), CYP17A1 (17-hydroxylase; 17-OH), CYP11A1 (P450 side-chain cleavage enzyme; P450scc) and HSD3B2 (3β hydroxysteroid dehydrogenase; 3βHSD) were amplified, cloned and expressed as 35S-methionine radiolabelled recombinant protein. In a pilot study, serum samples from 20 dogs with hypoadrenocorticism and four unaffected control dogs were screened by radio-immunoprecipitation assay. There was no evidence of reactivity against 21-OH, 17-OH or 3βHSD, but five dogs with hypoadrenocorticism showed immunoreactivity to P450scc compared with controls. Serum samples were subsequently obtained from 213 dogs diagnosed with hypoadrenocorticism and 110 dogs from a hospital control population. Thirty control dogs were randomly selected to establish a threshold for antibody positivity (mean + 3 × standard deviation). Dogs with hypoadrenocorticism were more likely to be P450scc autoantibody positive than hospital controls (24% vs. 1.2%, respectively; p = 0.0016). Sex was significantly associated with the presence of P450scc autoantibodies in the case population, with 30% of females testing positive compared with 17% of males (p = 0.037). Significant associations with breed (p = 0.015) and DLA-type (DQA1*006:01 allele; p = 0.017) were also found. This cross-sectional study indicates that P450scc autoantibodies are present in a proportion of dogs affected with hypoadrenocorticism.

Expression and clinical relevance of paired box protein 7 and sex determining region Y-box 2 in canine corticotroph pituitary adenomas

Pituitary-dependent hypercortisolism is a common endocrinopathy in dogs, caused by an adrenocorticotrophic hormone secreting pituitary tumour of the anterior or intermediate lobe. The prognosis of intermediate lobe adenomas is worse than that of anterior lobe adenomas, indicating the possible usefulness of melanotropic markers as prognosticators. Another possible origin of pituitary adenomas is found in cancer stem cells. The aim of the present study was to investigate the expression of melanotroph specific transcription factor paired box protein 7 (Pax7) and stem cell marker and reprogramming factor sex determining region Y-box 2 (Sox2) and to relate their expression to clinical parameters. The mean ± SD of labelling index (LI) for Pax7 was 8.6% ± 21.7% in the adenomas; 1/6 controls had positive staining (LI, 15.2%). For Sox2, the LI in the adenomas was 16.9% ± 15.2% and 19.5% ± 11.6% in the controls. Pax7 expression was significantly higher in enlarged pituitaries, compared to non-enlarged pituitaries (P = 0.05), but Pax7 or Sox2 immunopositivity did not correlate to other clinical parameters such as histological diagnosis, survival time or disease-free interval. Gene expression of Pax7 target genes, such as proconvertase 2 (PC2), pro-opiomelanocortin (POMC), and dopamine D2 receptor (DRD2), was significantly lower in the adenoma samples compared to normal tissue, indicating that Pax7 signalling was not activated in adenomas. It was suggested that Pax7 and Sox2 remain interesting targets for molecular investigations into their role in pituitary tumorigenesis, but were unsuitable as clinical prognosticators in dogs.