Incidence, complications and therapeutic evaluation of clinical hypothyroidism in different breeds of dogs

This 2025 clinical study published in BMC Veterinary Research investigated how often hypothyroidism is the underlying cause in dogs presenting with common concerns like hair loss or obesity. The researchers aimed to clarify whether these everyday clinical signs are frequently linked to thyroid dysfunction, how the condition progresses when unrecognized, and how dogs respond to treatment. The findings show that hypothyroidism is not uncommon in these cases and can affect multiple body systems when it advances.

Last Reviewed Date: 04/10/2026

Overview

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Elgalfy, G. E., Ghanem, M. M., Helal, M. A. Y., & El-khaiat, H. M. (2025). Incidence, complications and therapeutic evaluation of clinical hypothyroidism in different breeds of dogs. BMC Veterinary Research, 21, 332. https://doi.org/10.1186/s12917-025-04746-4

Study Design And Purpose

This was a clinical observational study conducted between 2022 and 2024, involving 212 dogs from veterinary clinics. Of these, 200 dogs were included because they showed dermatological changes such as alopecia or signs of obesity, while a smaller group of healthy dogs served as controls.

The purpose of the study was threefold:

To determine how often hypothyroidism is diagnosed in dogs with these common clinical signs
To document the types of complications seen in more severely affected dogs
To evaluate how dogs respond to treatment with levothyroxine

Rather than focusing only on already diagnosed cases, the study examined dogs at the point of initial presentation, after excluding other possible causes.

Incidence Of Hypothyroidism In The Study Population

After ruling out other causes of alopecia and obesity, hypothyroidism was confirmed in 28 out of 200 dogs, representing 14 percent of the cases studied.

The study also reported patterns within this group:

Higher occurrence in middle-aged dogs
Greater incidence in certain breeds, including Golden Retrievers
Slightly higher prevalence in males compared to females

Hypothyroidism was identified more frequently in dogs that showed both skin changes and obesity compared to those with only one of these signs.

Clinical Signs Observed In Affected Dogs

The study documented a range of clinical signs in dogs diagnosed with hypothyroidism.

The most common findings included:

Dermatological changes such as non-itchy hair loss and coat abnormalities
Metabolic changes including weight gain despite normal appetite
Behavioral changes such as lethargy and reduced activity

These signs were often present in the same dogs, reflecting the role of thyroid hormones in regulating multiple functions in the body.

Complications In More Severely Affected Dogs

In dogs with more advanced hypothyroidism, additional complications were observed across several body systems.

These included:

Skin conditions such as thickened skin, infections, and more extensive hair loss
Cardiovascular and respiratory changes, including reduced exercise tolerance and fluid accumulation
Neuromuscular signs such as coordination issues and weakness
Gastrointestinal problems, including vomiting and esophageal dilation
Reproductive abnormalities, including infertility

These findings show that the condition can extend beyond early signs when it becomes more severe.

Diagnostic Approach Used In The Study

Diagnosis of hypothyroidism in this study was based on both clinical signs and laboratory testing.

Dogs diagnosed with hypothyroidism showed:

Decreased levels of total and free thyroxine
Increased levels of thyroid stimulating hormone

In some cases, thyroglobulin autoantibodies were also detected, indicating an immune-related component affecting the thyroid gland.

The study emphasizes that laboratory results were interpreted alongside clinical findings to confirm diagnosis.

Response To Levothyroxine Treatment

Dogs diagnosed with hypothyroidism were treated with levothyroxine, a synthetic form of thyroid hormone.

The study reported:

Improvement in activity and behavior within the first week
Changes in hormone levels within the first month
Gradual improvement in body weight and skin condition over several months
Hair regrowth beginning within the first month and continuing over time

Treatment was described as ongoing, with dosage adjusted based on response and follow-up testing.

Study Limitations And Considerations

The researchers note several factors that can affect how these findings are interpreted.

The study focused specifically on dogs already showing dermatological changes or obesity, which means the reported incidence reflects this selected group rather than the general dog population. Dogs without these signs were not included in the main analysis.

Diagnosis of hypothyroidism can also be influenced by other illnesses or medications, which may alter thyroid hormone levels. While the study excluded dogs with known interfering conditions, the authors acknowledge that thyroid testing can still be complex and requires careful interpretation.

In addition, the number of dogs diagnosed with hypothyroidism was relatively small compared to the overall sample. This may limit how broadly the findings can be applied across all breeds and populations.

The researchers also recommend further studies with larger sample sizes to better understand long-term complications and refine diagnostic approaches.

Why These Findings Matter In Practice

This study provides a clear view of how hypothyroidism appears in dogs that present with common clinical concerns. By focusing on dogs with alopecia or obesity and evaluating them systematically, the researchers showed that hypothyroidism is one possible underlying cause in these cases.

The findings also show that the condition can involve multiple body systems and may become more complex over time if not identified and treated. For this reason, the study supports including thyroid evaluation as part of the diagnostic process when these types of signs are present.

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General Health Topics

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Image & Title	Info Column
Cardiovascular & Blood	At a Glance The cardiovascular system includes the heart and blood vessels, which transport oxygen and nutrients throughout the body. Blood health is equally important, as it carries immune cells, regulates clotting, and removes waste. Conditions like heart disease, anemia, or blood clotting disorders can severely impact a dog’s energy, endurance, and longevity. Connecting the Dots Thyroid hormones influence heart rate, myocardial relaxation, and vascular resistance. The study identified exercise intolerance, edema, and echocardiographic evidence of diastolic dysfunction (reduced E/A ratio). Radiographs also showed pulmonary edema in severe cases, indicating impaired cardiac function affecting circulation.
Digestion & Gastrointestinal	At a Glance The digestive and gastrointestinal systems break down food, absorb nutrients, and eliminate waste. When disrupted by inflammation, infection, or food sensitivities, they can cause discomfort, nutrient deficiencies, and broader health issues. Healthy digestion is essential to a dog’s overall well-being. Connecting the Dots Normal gastrointestinal motility depends on coordinated neuromuscular function and metabolic regulation. In this study, some hypothyroid dogs presented with vomiting and were found to have esophageal dilation on radiographs. This reflects impaired movement of food through the esophagus associated with thyroid hormone deficiency.
Endocrine & Metabolic	At a Glance The endocrine and metabolic systems regulate how a dog’s body produces energy, maintains tissues, and responds to changing internal conditions. The endocrine system is made up of hormone-producing glands such as the thyroid, pancreas, adrenal glands, and pituitary. These glands release chemical signals that travel through the bloodstream and instruct cells how quickly to use energy, store nutrients, and repair tissues. Because hormones influence nearly every organ, disruptions in endocrine signaling often appear as patterns of changes across the body, affecting energy levels, body weight, skin and coat health, digestion, immune function, and stress responses. Connecting the Dots Thyroid hormones regulate metabolic rate, energy utilization, and body weight in dogs. The study shows that reduced thyroxine leads to weight gain despite normal appetite and reduced activity levels. It also documents decreased TT4/FT4 and elevated TSH, confirming systemic metabolic slowdown driven by endocrine dysfunction.
Immune System	At a Glance The immune system is a complex, body-wide network that protects dogs from infections, helps resolve injury, and monitors for internal abnormalities. It also plays a role in regulating inflammation and maintaining tolerance to non-harmful exposures such as food proteins or pollen. A well-regulated immune system allows dogs to recover from illness efficiently and respond appropriately to everyday challenges without damaging healthy tissue. Connecting the Dots The immune system regulates defense against pathogens and can contribute to disease when it targets the body’s own tissues. In some dogs in this study, thyroglobulin autoantibodies (TgAA) were detected, indicating immune-mediated damage to the thyroid gland. These cases also showed recurrent skin infections, suggesting reduced immune resilience associated with low thyroid hormone levels.
Neurological & Cognitive	At a Glance Neurological and cognitive health in dogs refers to how the brain, spinal cord, and nervous system process information, control movement, and regulate behavior. This system shapes everything from memory and learning to coordination and emotional response. When function is balanced, dogs remain alert, responsive, and adaptable. When disruption occurs, changes often show up as disorientation, altered behavior, slowed learning, or loss of coordination. Connecting the Dots Peripheral nerves and neuromuscular function rely on proper metabolic support and tissue integrity. In this study, some hypothyroid dogs showed neurological signs including ataxia and hind limb weakness. These signs are associated with nerve dysfunction and tissue changes that can interfere with normal motor control.
Respiratory System	At a Glance Respiratory health in dogs involves how air moves into the lungs, how oxygen enters the bloodstream, and how carbon dioxide is removed from the body. This system supports every cell by delivering oxygen needed for energy production. When functioning well, breathing is quiet, steady, and effortless. When disrupted, dogs may show coughing, labored breathing, reduced stamina, or conditions like kennel cough, pneumonia, or airway obstruction. Connecting the Dots Respiratory function can be affected when cardiac dysfunction or fluid accumulation alters lung performance. The study documents cough, labored breathing, cyanosis, and crackles on chest exam in affected dogs. Imaging confirmed pulmonary edema, showing fluid buildup in the lungs associated with advanced disease.
Skin & Coat	At a Glance A dog’s skin and coat are vital to its overall health, providing protection, temperature regulation, and sensory functions. Healthy skin and a shiny coat are often signs of proper nutrition and care. Issues such as dryness, itching, or excessive shedding may indicate underlying health problems like allergies or infections. Maintaining good skin and coat health is key to a dog’s comfort and well-being, making it an important aspect of overall care. Connecting the Dots Hair growth and skin turnover depend on thyroid hormone signaling to maintain the anagen (active growth) phase of hair follicles. The study reports widespread alopecia, dry brittle coat, hyperpigmentation, seborrhea, and myxedema in affected dogs. It explains that low thyroxine shifts follicles into the telogen phase, which is the resting stage where hair stops growing and is eventually shed without being replaced.

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Health Conditions

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Image & Title	Info Column
Hypothyroidism	At a Glance Hypothyroidism in dogs occurs when the thyroid gland does not produce enough thyroid hormone, leading to a gradual slowdown of metabolic activity throughout the body. Because these hormones regulate how cells produce energy, maintain skin and hair follicles, and support muscle and organ function, low levels can affect many systems at once. Dogs may develop changes such as reduced energy, unexplained weight gain, thinning or dull coat, skin thickening, sensitivity to cold, or subtle shifts in muscle tone and facial structure. Connecting the Dots Hypothyroidism develops when the thyroid gland does not produce enough thyroid hormone, lowering TT4 and FT4 and increasing TSH as pituitary feedback rises. The study diagnosed hypothyroid dogs by combining thyroid testing with clinical findings such as alopecia, obesity, lethargy, and reduced activity after ruling out other causes of skin disease and weight gain. It also shows how untreated disease can progress beyond these early signs into pyoderma, myxedema, megaesophagus, neurologic deficits, infertility, and cardiac dysfunction before improving with levothyroxine treatment.
Vomiting	At a Glance Dog vomiting is a protective reflex, not a disease, designed to remove material the body cannot tolerate or process properly. It is coordinated by the brain but often triggered by signals from the digestive tract, bloodstream, or nervous system. In dogs, vomiting can range from an occasional, self-limited event to a sign of deeper disruption in digestion, gut motility, or systemic balance. Understanding the type of vomiting, its timing, and its triggers helps distinguish normal responses from patterns that require medical attention. Connecting the Dots Vomiting can result from dysfunction in the upper gastrointestinal tract, including impaired esophageal motility. In this study, some hypothyroid dogs regurgitated food shortly after eating and were found to have esophageal dilation on radiographs. This reflects reduced movement of food through the esophagus, which can occur in hypothyroidism due to neuromuscular impairment.