Cushing's Disease in Dogs: Symptoms, Testing, Treatment, and Long-Term Monitoring

This article is educational and is not a substitute for veterinary diagnosis or treatment.

At a Glance: Key Points for Owners and Clinicians

Introduction

Cushing's disease in dogs, also known as canine hyperadrenocorticism (HAC), is one of the most common endocrine disorders encountered in small animal practice. The condition results from chronic exposure to excessive glucocorticoids, primarily cortisol, which produces a characteristic constellation of clinical signs and systemic complications. In the vast majority of cases (80-85%), hyperadrenocorticism is pituitary-dependent (Cushing's disease), caused by an adrenocorticotropic hormone (ACTH)-secreting adenoma of the pituitary gland. The remaining 15-20% of cases are adrenal-dependent, arising from a functional adrenal tumor that autonomously secretes cortisol [1].

The genomic landscape of Cushing's disease in dogs shares remarkable similarities with the human condition. A 2021 study by Wang et al. identified eight genes significantly overexpressed across both human and canine corticotroph pituitary adenomas, including MAMLD1, MNX1, RASEF, TBX19, BIRC5, TK1, GLDC, and FAM131B [1]. Notably, MAMLD1 was found to be positively expressed in the nucleus of ACTH-secreting tumor cells in 70.9% of human cases but absent in healthy pituitary tissue, suggesting a potential diagnostic target and reinforcing the value of the canine model for translational research [1].

Spontaneous Cushing's disease in dogs provides a naturally occurring model that closely mirrors the human condition. Dogs develop ACTH-producing pituitary adenomas spontaneously, unlike laboratory rodents that require genetic manipulation or chemical induction [2]. This makes canine patients uniquely valuable for studying disease pathogenesis and testing novel therapeutics.

Pathophysiology and Classification

Normal Hypothalamic-Pituitary-Adrenal Axis

The hypothalamic-pituitary-adrenal (HPA) axis regulates cortisol production through a negative feedback loop. Corticotropin-releasing hormone (CRH) from the hypothalamus stimulates the pituitary to release ACTH, which in turn triggers cortisol secretion from the adrenal cortex. Cortisol then feeds back to suppress further CRH and ACTH release. In Cushing's disease, this feedback mechanism is disrupted by autonomous ACTH secretion from a pituitary adenoma.

Pituitary-Dependent Hyperadrenocorticism (PDH)

Pituitary-dependent hyperadrenocorticism accounts for the majority of spontaneous cases. The pituitary adenoma secretes ACTH in an unregulated manner, leading to bilateral adrenal hyperplasia and excessive cortisol production. These adenomas are typically small (microadenomas less than 10 mm) and benign. Genomic profiling has revealed that these tumors overexpress several genes involved in cell proliferation and hormone synthesis, including the transcription factor TBX19 and the cell cycle regulator BIRC5 [1].

Adrenal-Dependent Hyperadrenocorticism (ADH)

Adrenal tumors, either adenomas or carcinomas, autonomously secrete cortisol independent of ACTH stimulation. This results in suppression of pituitary ACTH production through negative feedback. Adrenal carcinomas tend to be larger, more invasive, and carry a poorer prognosis. A case report by Melián et al. described a 14-year-old dog with an adrenal cortical carcinoma that caused multiple pathological bone fractures, a rare but severe complication [10].

Atypical Hyperadrenocorticism

A subset of dogs presents with clinical signs consistent with hyperadrenocorticism but has normal baseline cortisol concentrations and negative results on standard suppression tests. This condition, termed atypical hyperadrenocorticism (AHAC), may involve excessive production of steroid hormone precursors such as progesterone, 17-hydroxyprogesterone, or androgens rather than cortisol [12]. Diagnosis requires ACTH stimulation testing with measurement of these alternative steroid metabolites. The extended low-dose dexamethasone suppression test (12-hour protocol) has been evaluated for detecting AHAC but did not reliably differentiate affected dogs from healthy controls in one study [13].

Clinical Signs and Symptoms

Classic Presentation

The classic clinical signs of Cushing's disease in dogs are well-recognized and reflect the systemic effects of chronic cortisol excess. Owners most commonly report:

Polyuria and Polydipsia (PU/PD): Increased thirst and urination are often the earliest and most noticeable signs. Cortisol interferes with antidiuretic hormone (ADH) action at the renal collecting ducts, impairing water reabsorption. Dogs may drink excessively and require frequent outdoor breaks or begin having accidents in the house.

Polyphagia: Increased appetite results from cortisol's stimulatory effect on appetite centers in the hypothalamus. Dogs may become food-obsessed, beg constantly, or steal food.

Pendulous Abdomen: Abdominal distension occurs due to muscle weakness and atrophy of the abdominal wall, combined with redistribution of fat to the abdominal cavity. This gives the characteristic "pot-bellied" appearance.

Dermatologic Changes: Alopecia (hair loss) is common, typically bilaterally symmetrical and sparing the head and extremities. The skin becomes thin, fragile, and hyperpigmented. Calcinosis cutis (deposition of calcium in the skin) can occur, presenting as firm, white plaques or papules.

Muscle Weakness and Muscle Atrophy: Cortisol promotes protein catabolism, leading to loss of muscle mass, particularly in the temporal and hindlimb muscles. Dogs may show reluctance to jump, climb stairs, or exercise.

Panting and Respiratory Signs: Increased respiratory rate and panting are common, even at rest. This may be due to weakness of respiratory muscles, increased abdominal pressure, or direct effects of cortisol on the respiratory center.

Recurrent Infections: Immunosuppression from cortisol excess predisposes dogs to recurrent urinary tract infections, skin infections, and respiratory infections.

Less Common and Severe Manifestations

Thromboembolic Complications: Dogs with hyperadrenocorticism are at increased risk of hypercoagulability and thromboembolism. A prospective study by Pace et al. found that 88.2% of newly diagnosed HAC dogs exhibited a hypercoagulable tendency, with abnormalities in multiple coagulation parameters [15]. This risk should be considered when planning surgical procedures.

Pathological Bone Fractures: Although osteoporosis is well-documented in human Cushing's syndrome, it has been rarely reported in dogs. Melián et al. described a case of multiple pathological rib and vertebral fractures in a dog with adrenal-dependent Cushing's syndrome, confirmed by computed tomography and postmortem examination [10]. Decreased bone density was evident in cervical and thoracic vertebrae, ribs, and scapular bones.

Oxidative Stress: Chronic cortisol excess induces systemic oxidative stress. Chen et al. demonstrated that dogs with hyperadrenocorticism had significantly elevated serum malondialdehyde (MDA), total oxidant status (TOS), and oxidative stress index (OSI) compared to healthy controls [8]. These markers improved after trilostane treatment.

Concurrent Disease Masking: Cushing's disease can mask other serious conditions. Choi et al. reported a case of T-cell chronic lymphocytic leukemia (CLL) that was initially hidden by the effects of hypercortisolism. After trilostane therapy normalized cortisol levels, lymphocytosis and nonregenerative anemia became apparent, leading to the diagnosis of CLL [4].

Impact on Quality of Life

The clinical signs of Cushing's syndrome significantly impair a dog's health-related quality of life (HRQoL). Schofield et al. developed and validated a 19-item HRQoL tool for dogs with Cushing's syndrome, finding that owners rated "owner impact" questions (such as the burden of care) as most important, while demeanor-related questions were rated lower [11]. Dogs receiving trilostane treatment had statistically better HRQoL scores than untreated dogs, underscoring the importance of medical management [11].

Diagnostic Approach

Initial Screening and Differential Diagnosis

The diagnostic workup begins with a thorough history and physical examination. Key differentials for the presenting signs include diabetes mellitus, chronic kidney disease, hyperthyroidism (in cats), acromegaly, and psychogenic polydipsia. Routine laboratory testing (complete blood count, serum biochemistry panel, urinalysis) often reveals supportive abnormalities:

• Complete Blood Count: Stress leukogram (neutrophilia, lymphopenia, eosinopenia), erythrocytosis
• Serum Biochemistry: Elevated alkaline phosphatase (ALP), alanine aminotransferase (ALT), cholesterol, and fasting glucose; mild hyperglycemia
• Urinalysis: Low urine specific gravity (isosthenuria or hyposthenuria), proteinuria, evidence of urinary tract infection

Machine Learning-Assisted Screening

Recent advances in machine learning offer promising tools for screening. Yoo et al. developed a gradient boosting algorithm using routine screening diagnostics (complete blood count, serum chemistry, urinalysis) that achieved 88.5% accuracy, 83.3% sensitivity, and 93.5% specificity for diagnosing Cushing's syndrome [6]. The model had an area under the receiver operating characteristic curve of 0.912, indicating excellent discriminatory ability. A user-friendly graphical interface was developed to facilitate clinical implementation [6].

Confirmatory Endocrine Testing

Low-Dose Dexamethasone Suppression Test (LDDST): This is the most sensitive test for confirming hyperadrenocorticism. Dexamethasone (0.01-0.015 mg/kg IV) is administered, and serum cortisol is measured at 0, 4, and 8 hours. In normal dogs, cortisol suppresses to below 1.4 mcg/dL (40 nmol/L) at 8 hours. Failure to suppress indicates hyperadrenocorticism. The LDDST also helps differentiate PDH from ADH: dogs with PDH may show suppression at 4 hours with escape at 8 hours, while dogs with ADH show no suppression at any time point [16].

ACTH Stimulation Test: This test measures the adrenal response to exogenous ACTH. Cortisol is measured before and 60 minutes after administration of synthetic ACTH (cosyntropin, 5 mcg/kg IV or IM). The ACTH stimulation test has high specificity but lower sensitivity compared to the LDDST. A negative result does not rule out hyperadrenocorticism [16].

Urine Cortisol:Creatinine Ratio (UCCR): This test measures cortisol excretion in a free-catch urine sample, normalized to creatinine. A normal UCCR effectively rules out hyperadrenocorticism (high negative predictive value). However, false positives are common due to stress or non-adrenal illness, so an abnormal result requires confirmation with a suppression test [16].

Differentiation of Pituitary vs. Adrenal Disease

Endogenous ACTH Measurement: Plasma ACTH concentration helps distinguish PDH from ADH. Dogs with PDH have normal to elevated ACTH, while dogs with ADH have suppressed ACTH (typically below the detection limit). Zeugswetter et al. found that using a chemiluminometric assay with a cut-off of 2.2 pmol/L, the sensitivity for diagnosing PDH was 0.82 and specificity was 1.0 [17]. However, 9 of 49 dogs with PDH had ACTH concentrations below the detection limit, indicating that additional discriminatory tests are needed in some cases [17].

High-Dose Dexamethasone Suppression Test (HDDST): Dexamethasone (0.1 mg/kg IV) is administered, and cortisol is measured at 0, 4, and 8 hours. Suppression of cortisol to less than 50% of baseline suggests PDH. This test correctly classifies approximately 75% of PDH cases.

Adrenal Imaging: Abdominal ultrasonography is used to assess adrenal gland size and symmetry. Bilateral enlargement suggests PDH, while a unilateral mass with contralateral atrophy suggests ADH. Computed tomography (CT) or magnetic resonance imaging (MRI) can further characterize adrenal masses and evaluate for pituitary enlargement.

Salivary Cortisol Testing

Salivary cortisol measurement offers a noninvasive alternative for diagnosis and monitoring. Meunier et al. evaluated in-hospital and at-home salivary sampling in healthy dogs and trilostane-treated dogs with Cushing's syndrome [7]. Saliva was collected using a ginger-dipped Salimetrics swab held in the dogs' mouths for 30 seconds. While sampling was successful in all healthy controls, success rates were lower in dogs with Cushing's syndrome (47% in-hospital, 39% at-home) [7]. This approach may be useful in selected patients but requires owner training and patient cooperation.

Novel Biomarkers

Calprotectin (S100A8/A9), a protein related to innate immunity and considered a biomarker of inflammation, has been investigated in canine hyperadrenocorticism. García-Camacho et al. validated an automated assay for calprotectin measurement in dog saliva and serum and found changes in dogs with hyperadrenocorticism, though the clinical utility requires further study [3].

Treatment Options

Medical Management: Trilostane

Trilostane (Vetoryl) is the current standard of care for medical management of both pituitary-dependent and adrenal-dependent hyperadrenocorticism in dogs. It is a competitive inhibitor of 3-beta-hydroxysteroid dehydrogenase, blocking the conversion of pregnenolone to progesterone and thereby reducing cortisol synthesis.

Dosing Protocol: The recommended starting dose is 1-3 mg/kg orally once daily with food. After 10-14 days, an ACTH stimulation test is performed 4-6 hours after the morning dose. The goal is to achieve a post-ACTH cortisol concentration between 1.5 and 5.4 mcg/dL (40-150 nmol/L). Dose adjustments are made based on clinical response and ACTH stimulation test results.

Efficacy and Safety: Chen et al. demonstrated that trilostane treatment (1 mg/kg twice daily for 45 days) significantly reduced oxidative stress markers in dogs with hyperadrenocorticism, including decreases in MDA, TOS, and OSI, with a nonsignificant increase in SOD activity [8]. Clinical improvement in signs such as polyuria, polydipsia, and appetite typically occurs within 2-4 weeks, while dermatologic improvement may take 3-6 months.

Monitoring Protocol: Long-term monitoring involves regular ACTH stimulation tests (every 3-6 months), clinical assessment, and monitoring for adverse effects including vomiting, diarrhea, lethargy, and weakness (signs of hypoadrenocorticism). The HRQoL tool developed by Schofield et al. can aid in objective assessment of treatment response [11].

Medical Management: Pasireotide (SOM230)

Pasireotide is a multiligand somatostatin analog that binds to somatostatin receptor subtypes 1, 2, 3, and 5. In a study by Castillo et al., pasireotide was tested in dogs with Cushing's disease over 6 months of continuous treatment or intermittent cycles [2]. The drug produced significant decreases in ACTH, urinary cortisol:creatinine ratio, and adenoma size on magnetic resonance imaging, with improvement in clinical signs and no significant side effects [2]. At the cellular level, pasireotide suppressed pro-opiomelanocortin (POMC) promoter activity through SSTR2 via the Gi alpha-subunit and reduced Nur77/Nurr1 transcriptional activity [2]. Pasireotide is not yet approved for veterinary use but represents a promising future therapeutic option.

Surgical Management

Transsphenoidal Hypophysectomy: Surgical removal of the pituitary adenoma via transsphenoidal approach is the definitive treatment for PDH. This procedure requires specialized equipment and expertise. A 2023 report described the use of 3D-printed surgical guides to improve accuracy during pituitary surgery in dogs with Cushing's disease [5]. Success rates are high in experienced centers, but complications include transient or permanent hypoadrenocorticism, diabetes insipidus, and neurologic deficits.

Adrenalectomy: Unilateral adrenalectomy is the treatment of choice for adrenal-dependent hyperadrenocorticism caused by a benign adenoma. Laparoscopic adrenalectomy is associated with less morbidity than open surgery. Adrenal carcinomas carry a guarded prognosis due to the risk of local invasion and metastasis.

Radiation Therapy

Radiation therapy is an option for pituitary macroadenomas that are not amenable to surgical resection. It can reduce tumor size and improve clinical signs, though the response may take months to develop.

Management of Concurrent Conditions

Hypercoagulability: Given the high prevalence of hypercoagulability in HAC dogs, clinicians should consider thromboembolic risk, especially before surgery. Pace et al. found that 88.2% of HAC dogs exhibited a hypercoagulable tendency, though individual coagulation assay abnormalities did not predict abnormalities in others [15].

Concurrent Disease: As demonstrated by Choi et al., Cushing's disease can mask other conditions such as chronic lymphocytic leukemia [4]. Clinicians should maintain a high index of suspicion for concurrent disease, particularly when unexpected laboratory abnormalities emerge after cortisol normalization.

Long-Term Monitoring

Clinical Assessment

Regular evaluation of clinical signs is the cornerstone of monitoring. Owners should be asked about:

• Water intake and urine output
• Appetite and weight changes
• Activity level and exercise tolerance
• Coat and skin condition
• Respiratory pattern and panting
• Quality of life indicators

Biochemical Monitoring

ACTH Stimulation Test: This is the standard test for monitoring trilostane therapy. It is performed 4-6 hours after the morning trilostane dose. The target post-ACTH cortisol concentration is 1.5-5.4 mcg/dL (40-150 nmol/L). Testing is recommended 10-14 days after any dose change and every 3-6 months in stable patients.

Salivary Cortisol: Salivary cortisol measurement using liquid chromatography high-resolution mass spectrometry (LC-HRMS) has been evaluated for monitoring trilostane-treated dogs. Meunier et al. found that while in-hospital and at-home sampling was feasible in healthy controls, success rates were lower in dogs with Cushing's syndrome [7]. This approach may be useful for selected patients but requires validation of sample collection techniques.

Oxidative Stress Markers: Chen et al. demonstrated that trilostane treatment effectively ameliorates oxidative stress in HAC dogs, with significant decreases in MDA, TOS, and OSI [8]. While not yet standard practice, monitoring oxidative stress markers may provide additional insight into disease control.

Quality of Life Assessment

The HRQoL tool developed by Schofield et al. provides a validated method for assessing the impact of Cushing's syndrome and its treatment on a dog's well-being [11]. The tool showed good internal consistency (Cronbach's alpha = 0.83) and correlated positively with owner assessment of their dog's quality of life. Dogs on trilostane treatment had statistically better HRQoL scores than untreated dogs [11].

Monitoring for Complications

Hypoadrenocorticism: Trilostane overdose or individual sensitivity can lead to iatrogenic hypoadrenocorticism (Addison's disease). Signs include vomiting, diarrhea, lethargy, weakness, and collapse. Electrolyte abnormalities (hyponatremia, hyperkalemia) may be present. Owners should be educated to recognize these signs and seek immediate veterinary care.

Adrenal Tumor Progression: In dogs with adrenal-dependent disease, regular abdominal ultrasonography is recommended to monitor for tumor growth, local invasion, or metastasis.

Cushing's Disease Masking Other Conditions: As highlighted by Choi et al., normalization of cortisol levels can unmask previously hidden conditions such as leukemia [4]. Clinicians should be alert to new or worsening clinical signs after treatment initiation.

Prognosis

The prognosis for dogs with Cushing's disease is generally good with appropriate treatment and monitoring. Median survival time for dogs with PDH treated with trilostane is approximately 2-3 years. Many dogs die from unrelated causes rather than from Cushing's disease itself. Factors associated with a poorer prognosis include:

• Presence of a pituitary macroadenoma with neurologic signs
• Adrenal carcinoma with local invasion or metastasis
• Poorly controlled disease with persistent clinical signs
• Development of thromboembolic complications
• Concurrent serious illness

Special Considerations

Breed Predispositions

Certain breeds appear to be at increased risk for Cushing's disease, including Poodles, Dachshunds, Beagles, Boxers, and Boston Terriers. The condition is most commonly diagnosed in middle-aged to older dogs (median age 10-12 years).

Iatrogenic Cushing's Syndrome

Chronic administration of exogenous glucocorticoids (oral, topical, or injectable) can produce clinical signs identical to spontaneous hyperadrenocorticism. Yamanaka et al. identified a truncated form of the glucocorticoid receptor in a dog with iatrogenic Cushing's syndrome that exhibited very low reactivity to prednisolone, suggesting individual differences in glucocorticoid sensitivity [19]. Diagnosis requires a history of glucocorticoid exposure and resolution of signs upon drug withdrawal.

Cushing's Syndrome in Other Species

While this article focuses on dogs, the diagnostic approach has been adapted for other species. Nógrádi et al. successfully applied a modified version of the canine low-dose dexamethasone suppression test to diagnose Cushing's syndrome in a guinea pig, demonstrating the cross-species utility of this testing protocol [9]. A literature review comparing hypercortisolism in guinea pigs and dogs revealed significant overlap in disease characteristics, though species-specific distinctions exist [20].

Clinical Reasoning Behind Diagnostic Test Selection

The diagnostic workup for canine hyperadrenocorticism requires careful clinical reasoning, as no single test is perfect for all situations. Understanding the strengths and limitations of each test helps clinicians make informed decisions and avoid diagnostic pitfalls.

When to Choose the Low-Dose Dexamethasone Suppression Test (LDDST): The LDDST is the most sensitive test for confirming hyperadrenocorticism, making it the preferred screening test when clinical suspicion is high. However, it is important to recognize that stress from non-adrenal illness can produce false-positive results. Dogs with concurrent conditions such as diabetes mellitus, chronic kidney disease, or inflammatory disorders may show inadequate cortisol suppression even in the absence of true hyperadrenocorticism. For this reason, the LDDST should ideally be performed when the dog is clinically stable and non-adrenal diseases are well-controlled. The test also provides differentiation information: a dog with PDH may show suppression at 4 hours with escape at 8 hours, while a dog with ADH shows no suppression at any time point. However, this differentiation is not absolute, and approximately 25% of PDH cases will not show the classic suppression pattern [16].

When to Choose the ACTH Stimulation Test: The ACTH stimulation test has higher specificity but lower sensitivity than the LDDST. This means a positive result is highly suggestive of hyperadrenocorticism, but a negative result does not rule out the disease. The ACTH stimulation test is particularly useful for monitoring trilostane therapy because it directly assesses adrenal reserve and helps guide dose adjustments. It is also the test of choice when iatrogenic Cushing's syndrome is suspected, as exogenous glucocorticoids suppress endogenous ACTH and cause adrenal atrophy, leading to a blunted response to ACTH stimulation. One important limitation is that the ACTH stimulation test may be falsely negative in dogs with mild or early disease, as cortisol secretion may still be partially suppressible [16].

When to Use the Urine Cortisol:Creatinine Ratio (UCCR): The UCCR is an excellent screening test due to its high negative predictive value. A normal UCCR effectively rules out hyperadrenocorticism, making it useful for excluding the disease in dogs with equivocal clinical signs. However, false positives are common due to stress, hospitalization, or non-adrenal illness. The UCCR is best performed on a urine sample collected at home by the owner to minimize stress-induced cortisol elevation. If the UCCR is elevated, it must be followed by a suppression test (LDDST or ACTH stimulation test) for confirmation. The UCCR is also useful for monitoring response to therapy, as a decreasing trend indicates improving cortisol control [16].

The Role of Endogenous ACTH Measurement: Measuring plasma ACTH concentration is the most reliable method for differentiating PDH from ADH. Dogs with PDH have normal to elevated ACTH, while dogs with ADH have suppressed ACTH. However, as Zeugswetter et al. demonstrated, some dogs with PDH may have ACTH concentrations below the detection limit, leading to misclassification [17]. This occurs because ACTH is secreted in a pulsatile manner, and a single measurement may capture a trough. For this reason, some clinicians recommend measuring ACTH on two separate occasions or combining ACTH measurement with adrenal imaging for definitive differentiation.

The Challenge of Atypical Hyperadrenocorticism: Atypical hyperadrenocorticism (AHAC) presents a diagnostic dilemma because affected dogs have clinical signs consistent with hyperadrenocorticism but normal cortisol concentrations on standard testing. These dogs may have excessive production of steroid hormone precursors such as progesterone, 17-hydroxyprogesterone, or androgens rather than cortisol [12]. Diagnosis requires ACTH stimulation testing with measurement of these alternative steroid metabolites. However, the extended low-dose dexamethasone suppression test (12-hour protocol) did not reliably differentiate affected dogs from healthy controls in one study, highlighting the need for specialized testing in suspected cases [13]. Clinicians should consider AHAC when a dog has classic clinical signs but negative results on standard cortisol-based testing.

Owner Observation and Preparation for a Veterinary Visit

Owners play a critical role in the diagnosis and management of Cushing's disease in dogs. Careful observation and documentation of clinical signs can significantly aid the veterinarian in making an accurate diagnosis and monitoring treatment response.

What Owners Should Observe and Record: Before the veterinary visit, owners should be encouraged to track specific behaviors and changes. The most important observations include:

• Water intake: Measure the amount of water consumed daily. A simple method is to fill the water bowl to a marked level each morning and measure how much is added to refill it to that level the next day. Normal water intake is approximately 30-60 mL per kg of body weight per day. Dogs with Cushing's disease often drink well above this range.

• Urination frequency and volume: Note how often the dog needs to go outside, whether accidents occur in the house, and whether the dog wakes at night to urinate. Owners should also observe urine color and clarity, as urinary tract infections are common in dogs with hyperadrenocorticism.

• Appetite changes: Document any increase in appetite, food-seeking behavior, or changes in food preferences. Dogs with Cushing's disease may become food-obsessed, steal food, or beg constantly.

• Activity level and exercise tolerance: Note any reluctance to jump, climb stairs, or go for walks. Muscle weakness and atrophy may manifest as difficulty rising or a stiff gait.

• Coat and skin condition: Observe for hair loss, thinning skin, bruising, or the development of firm white plaques (calcinosis cutis). Note the pattern of hair loss, as Cushing's disease typically causes bilateral symmetrical alopecia sparing the head and extremities.

• Respiratory pattern: Document any increased panting, especially at rest or during mild activity. Panting may be more noticeable at night or in cool environments.

• Body condition: Note any abdominal distension (pot-bellied appearance) or weight gain, particularly around the abdomen.

Preparing for the Veterinary Visit: Owners should bring a written log of their observations, including dates and specific examples. They should also bring any previous medical records, including laboratory results and imaging studies. It is helpful for owners to prepare a list of questions, such as:

• What tests are needed to confirm the diagnosis?
• How long will it take to get results?
• What treatment options are available?
• What are the potential side effects of treatment?
• How often will my dog need to be monitored?
• What is the expected prognosis?

The Importance of Baseline Documentation: Before starting treatment, it is essential to establish baseline measurements for monitoring. Owners should record their dog's weight, water intake, and urine output. Photographs of the dog's coat, skin, and body condition can be helpful for documenting changes over time. The health-related quality-of-life (HRQoL) tool developed by Schofield et al. can be used to objectively assess the impact of the disease and treatment on the dog's well-being [11]. Owners should complete this tool before treatment and at regular intervals thereafter.

Recognizing Emergency Signs: Owners should be educated to recognize signs that require immediate veterinary attention, including:

• Vomiting, diarrhea, or loss of appetite (possible hypoadrenocorticism)
• Severe lethargy or weakness
• Collapse or seizures
• Difficulty breathing
• Sudden onset of lameness or pain (possible pathological fracture)
• Blood in urine or straining to urinate (possible urinary tract infection)

Prevention and Early Detection

Is Cushing's Disease Preventable? Currently, there is no known way to prevent spontaneous Cushing's disease in dogs. The condition arises from the development of a pituitary or adrenal tumor, and the underlying causes are not fully understood. However, certain measures may reduce the risk of iatrogenic Cushing's syndrome, which is caused by exogenous glucocorticoid administration.

Preventing Iatrogenic Cushing's Syndrome: Iatrogenic Cushing's syndrome can be prevented by using glucocorticoids judiciously and at the lowest effective dose for the shortest duration possible. When long-term glucocorticoid therapy is necessary, alternate-day dosing may reduce the risk of adrenal suppression and clinical signs. Owners should be aware that topical, otic, and ophthalmic glucocorticoid preparations can also be absorbed systemically and cause iatrogenic Cushing's syndrome, especially with prolonged use. Yamanaka et al. identified a truncated form of the glucocorticoid receptor in a dog with iatrogenic Cushing's syndrome that exhibited very low reactivity to prednisolone, suggesting individual differences in glucocorticoid sensitivity [19]. This finding underscores the importance of individualizing glucocorticoid therapy and monitoring for adverse effects.

The Role of Early Detection: Early detection of Cushing's disease can improve outcomes by allowing prompt treatment before significant complications develop. Owners should be educated about the early signs of Cushing's disease, particularly polyuria, polydipsia, and polyphagia. Routine wellness examinations, including annual blood work and urinalysis, may help identify abnormalities such as elevated alkaline phosphatase (ALP) or low urine specific gravity that warrant further investigation.

Screening High-Risk Breeds: Certain breeds appear to be at increased risk for Cushing's disease, including Poodles, Dachshunds, Beagles, Boxers, and Boston Terriers. Owners of these breeds should be particularly vigilant for early signs. Routine screening with urine cortisol:creatinine ratio or machine learning-assisted screening tools may be considered for high-risk breeds, especially in middle-aged to older dogs [6].

The Potential of Machine Learning for Screening: Yoo et al. developed a gradient boosting algorithm using routine screening diagnostics that achieved 88.5% accuracy, 83.3% sensitivity, and 93.5% specificity for diagnosing Cushing's syndrome [6]. This tool could potentially be used for early detection in at-risk populations, though further validation is needed before widespread implementation.

Prognosis and Long-Term Outcomes

Factors Influencing Prognosis: The prognosis for dogs with Cushing's disease is generally good with appropriate treatment and monitoring. Median survival time for dogs with PDH treated with trilostane is approximately 2-3 years, and many dogs die from unrelated causes rather than from Cushing's disease itself. However, several factors can influence prognosis:

• Tumor type and size: Dogs with pituitary microadenomas generally have a better prognosis than those with macroadenomas, which may cause neurologic signs. Adrenal carcinomas carry a guarded prognosis due to the risk of local invasion and metastasis.

• Response to treatment: Dogs that achieve good clinical control with trilostane therapy have a better prognosis than those with persistent clinical signs. Regular monitoring and dose adjustments are essential for maintaining control.

• Concurrent disease: The presence of other serious illnesses, such as heart disease, kidney disease, or cancer, can worsen prognosis. As demonstrated by Choi et al., Cushing's disease can mask other conditions such as chronic lymphocytic leukemia, which may become apparent only after cortisol normalization [4].

• Complications: Development of thromboembolic complications, pathological fractures, or severe infections can significantly worsen prognosis. Pace et al. found that 88.2% of HAC dogs exhibited a hypercoagulable tendency, highlighting the importance of monitoring for thromboembolic events [15].

Quality of Life Considerations: The health-related quality-of-life (HRQoL) tool developed by Schofield et al. provides a validated method for assessing the impact of Cushing's syndrome and its treatment on a dog's well-being [11]. Dogs receiving trilostane treatment had statistically better HRQoL scores than untreated dogs, underscoring the importance of medical management. Owners should be encouraged to complete the HRQoL tool at regular intervals to objectively assess treatment response and identify areas of concern.

Long-Term Monitoring for Complications: Long-term monitoring is essential for detecting and managing complications. Regular ACTH stimulation tests (every 3-6 months) help ensure appropriate trilostane dosing and prevent iatrogenic hypoadrenocorticism. Abdominal ultrasonography is recommended for dogs with adrenal-dependent disease to monitor for tumor growth, local invasion, or metastasis. Owners should be educated to recognize signs of hypoadrenocorticism, including vomiting, diarrhea, lethargy, and weakness, and to seek immediate veterinary care if these signs occur.

Special-Population Considerations

Geriatric Dogs: Cushing's disease is most commonly diagnosed in middle-aged to older dogs (median age 10-12 years). Geriatric dogs may have concurrent age-related conditions such as osteoarthritis, cognitive dysfunction, heart disease, or kidney disease that can complicate diagnosis and management. The clinical signs of Cushing's disease may be attributed to aging, leading to delayed diagnosis. Conversely, treatment of Cushing's disease may unmask or exacerbate other conditions. For example, trilostane therapy can cause electrolyte imbalances that may be poorly tolerated in dogs with heart disease or kidney disease. Careful monitoring and dose adjustments are essential in this population.

Dogs with Concurrent Endocrine Disease: Cushing's disease can coexist with other endocrine disorders, such as diabetes mellitus or hypothyroidism. The clinical signs of these conditions may overlap, making diagnosis challenging. For example, both Cushing's disease and diabetes mellitus can cause polyuria, polydipsia, and polyphagia. In dogs with both conditions, treatment of Cushing's disease may improve diabetic control, as cortisol antagonizes insulin action. Conversely, treatment of diabetes mellitus may unmask Cushing's disease by improving clinical signs and revealing persistent abnormalities.

Dogs with Pituitary Macroadenomas: Pituitary macroadenomas (greater than 10 mm) can cause neurologic signs such as lethargy, depression, circling, or visual deficits. These dogs have a poorer prognosis and may require more aggressive treatment, such as transsphenoidal hypophysectomy or radiation therapy. A 2023 report described the use of 3D-printed surgical guides to improve accuracy during pituitary surgery in dogs with Cushing's disease, offering hope for improved outcomes in this challenging population [5].

Dogs with Adrenal Carcinomas: Adrenal carcinomas are malignant tumors that can invade local tissues and metastasize to distant sites. These dogs have a guarded prognosis, and treatment may involve surgical removal (adrenalectomy) followed by medical management with trilostane if residual disease is present. Regular abdominal ultrasonography is recommended to monitor for tumor progression. A case report by Melián et al. described a 14-year-old dog with an adrenal cortical carcinoma that caused multiple pathological bone fractures, a rare but severe complication [10].

Dogs with Iatrogenic Cushing's Syndrome: Iatrogenic Cushing's syndrome is caused by chronic administration of exogenous glucocorticoids. Diagnosis requires a history of glucocorticoid exposure and resolution of clinical signs upon drug withdrawal. Treatment involves gradual tapering of glucocorticoids to allow recovery of the HPA axis. In some cases, alternative immunosuppressive medications may be used to replace glucocorticoids. Yamanaka et al. identified a truncated form of the glucocorticoid receptor in a dog with iatrogenic Cushing's syndrome that exhibited very low reactivity to prednisolone, suggesting individual differences in glucocorticoid sensitivity [19]. This finding underscores the importance of individualizing glucocorticoid therapy and monitoring for adverse effects.

Dogs with Concurrent Infections: Immunosuppression from cortisol excess predisposes dogs to recurrent infections, particularly urinary tract infections, skin infections, and respiratory infections. These infections may be difficult to treat and may require prolonged antibiotic therapy. Owners should be educated to recognize signs of infection, such as fever, lethargy, discharge, or changes in urination, and to seek veterinary care promptly. Routine urinalysis is recommended to screen for urinary tract infections, as dogs with Cushing's disease may not show typical clinical signs.

Frequently Asked Questions

1. What are the first signs of Cushing's disease in dogs?

The earliest and most common signs are increased thirst (polydipsia) and increased urination (polyuria). Owners often notice their dog drinking more water, needing more frequent bathroom breaks, or having accidents in the house. Increased appetite (polyphagia) is also an early sign in many dogs.

2. How is Cushing's disease diagnosed in dogs?

Diagnosis involves a combination of routine blood work, urinalysis, and specific endocrine tests. The low-dose dexamethasone suppression test (LDDST) is the most sensitive screening test. The ACTH stimulation test is also commonly used. Differentiation between pituitary-dependent and adrenal-dependent disease requires measurement of endogenous ACTH and adrenal imaging.

3. What is the treatment for Cushing's disease in dogs?

The primary medical treatment is trilostane (Vetoryl), a drug that inhibits cortisol production. It is given orally once or twice daily. Surgical options include transsphenoidal hypophysectomy for pituitary tumors and adrenalectomy for adrenal tumors. Pasireotide, a somatostatin analog, has shown promise in clinical trials but is not yet approved for veterinary use.

4. Is Cushing's disease painful for dogs?

Cushing's disease itself is not typically painful, but it can cause discomfort through muscle weakness, thinning skin, recurrent infections, and in rare cases, pathological bone fractures. The condition significantly impacts quality of life, and treatment can improve comfort and well-being.

5. Can Cushing's disease be cured in dogs?

Pituitary-dependent Cushing's disease can be cured by transsphenoidal hypophysectomy, but this procedure is available only at specialized referral centers. Adrenal-dependent disease can be cured by surgical removal of the adrenal tumor. Medical management with trilostane controls the disease but does not cure it, requiring lifelong treatment.

6. How long can a dog live with Cushing's disease?

With appropriate treatment and monitoring, dogs with Cushing's disease can live 2-3 years or longer after diagnosis. Many dogs die from unrelated causes such as cancer, heart disease, or kidney failure rather than from Cushing's disease itself.

7. What are the side effects of trilostane treatment?

Common side effects include vomiting, diarrhea, lethargy, and decreased appetite. These may indicate that the dose is too high or that the dog has developed hypoadrenocorticism (Addison's disease). Serious side effects require immediate veterinary attention. Regular monitoring with ACTH stimulation tests helps prevent complications.

8. Can diet help manage Cushing's disease in dogs?

Diet alone cannot treat Cushing's disease, but a balanced, high-quality diet can support overall health. Some veterinarians recommend a diet lower in fat and higher in fiber to help manage weight and blood sugar. Supplements such as melatonin, lignans, and milk thistle have been suggested anecdotally but lack strong evidence and should not replace medical treatment.

Related Veterinary Guides

• Canine Diabetes Mellitus: Diagnosis and Management
• Hypothyroidism in Dogs: Clinical Signs and Treatment
• Addison's Disease in Dogs: A Diagnostic Challenge
• Urinary Tract Infections in Dogs: A Clinical Approach
• Geriatric Canine Wellness: Comprehensive Care for Senior Dogs

References

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