Incidence and haemato-biochemical alterations in dermatoses associated with hypothyroidism in dogs

Introduction

Originating from Canis lupus, dogs are believed to have begun scavenging near human settlements, initiating the domestication process. Today, dogs are globally distributed, with an estimated population of nearly 700 million. In India, the pet dog population was approximately 19.5 million in 2018 and is projected to exceed 50 million by 2030. A healthy, glossy coat is one of the most valued aesthetic features of dogs and is often perceived as a reflection of good health (Smith et al., 2019) [1] . Skin disorders are among the most common reasons for veterinary consultation, accounting for approximately 12-75% of primary or secondary complaints in small animal practice (Scott and Paradis, 1990) [2] . Canine dermatoses may arise from a wide range of environmental and internal factors, including infections, parasitic infestations, allergic conditions and endocrine disorders. Alopecia unrelated to inflammatory or infectious causes is particularly distressing and may result in chronic morbidity, financial burden and, in severe cases, euthanasia (Medleau and Hnilica, 2006) [3] . Endocrine disorders frequently manifest with dermatological signs, as hormones such as thyroxine, cortisol and oestrogen play critical roles in hair growth and skin homeostasis. Endocrine dermatoses, commonly associated with hypothyroidism, hyperadrenocorticism and hyperestrogenism, are major causes of bilateral symmetrical alopecia in dogs (Credille et al., 2001) [4] . Hypothyroidism is the most prevalent endocrine disorder in dogs and results from deficient production of thyroid hormones, thyroxine (T 4 ) and triiodothyronine (T 3 ). Based on the site of dysfunction, hypothyroidism may be primary, secondary or tertiary, with over 95% of cases being primary in origin due to lymphocytic thyroiditis or idiopathic thyroid atrophy (Ettinger et al., 2017) [5] . Clinically, hypothyroid dogs commonly exhibit bilateral symmetrical alopecia, seborrhoea, delayed hair regrowth, obesity, lethargy, hyper pigmentation and recurrent pyoderma. Characteristic hair loss occurs over frictional areas, pressure points and the tail, producing a "rat-tail" appearance, while selective loss of guard hairs imparts a puppy-like coat (Feldman et al., 2004) [6] . Diagnosis relies on clinical signs supported by laboratory findings, typically low serum T 4 concentrations with elevated thyroidstimulating hormone levels. Levothyroxine (LT 4 ) remains the treatment of choice and is generally administered lifelong. Appropriate therapy leads to significant clinical improvement, though regular monitoring is essential to optimize dosage and ensure long-term therapeutic success (Elgalfy et al., 2025) [7] .

Materials and Methods

The study on "Incidence and haemato-biochemical and hormonal alterations in dermatoses associated with hypothyroidism in Dogs" was conducted at the Department of Veterinary Medicine, College of Veterinary Science and Animal Husbandry, Kamdhenu University, Navsari, Gujarat, from March to August 2025. Initially, dogs presented at Veterinary Clinical Complex, Navsari with dermatological lesions such as alopecia, seborrhoea, and recurrent skin infections along with clinical signs suggestive of hypothyroidism were screened. Samples including skin scrapings, impression smears, pus/exudate swabs and blood/serum were collected at the time of first presentation for diagnostic evaluation. Impression smears were prepared by pressing clean glass slides onto clipped lesions, air-dried, methanol-fixed and stained with new methylene blue before microscopic examination (Muse, 2000) [8] . Deep skin scrapings were obtained using a dulled scalpel blade until capillary oozing appeared; samples were processed in 10% KOH, centrifuged and examined microscopically for mites based on morphological features (Soulsby, 1986; Hnilica and Patterson, 2016) [9,10] . Swabs from deep and superficial purulent lesions were collected aseptically for bacterial culture and identification, following appropriate lesion preparation to minimize contamination, and antimicrobial susceptibility was determined using the Kirby-Bauer disc diffusion method (CLSI, 2017) [11] . Various haematological parameters were estimated using automatic blood cell counter, while, serum biochemical parameters were analyzed using commercially available diagnostic kits in a semi-automatic biochemical analyzer. Quantitative analysis of free T 4 , Total thyroxine (TT4) and TSH was carried out using the Chemiluminescent Immunoassay (CLIA) method, with the results expressed in ng/dL, µg/dl, and µIU/mL, respectively (Nelson and Couto, 2020) [12] .

Results and Discussion

Overall, Age, Sex and Breed-wise Incidence During the study, a total of 1867 cases of dogs were registered at Veterinary Clinical Complex for medical treatment. Of which, 720 cases were fresh cases and the rest were as follow up cases. Among 720 fresh cases, 19 were suspected for dermatoses associated with hypothyroidism based on clinical sings. Of which, 12 cases were identified as cases of dermatoses associated with hypothyroidism in dog with overall incidence of 1.67% (12/720). The hospitalbased incidence among the suspected cases was 63.16% (12/19). During study, the highest incidence of dermatoses associated with hypothyroidism was observed in dogs aged between 6-10 years (50.0 %) followed by2.5-6-year (25.00%) and >10-year (25.00%) age group with statistically non-significant difference between groups (Table 1). Similarly, Gupta (2016) [13] observed that the majority of affected dogs were between 5 and 10 years old (16 cases; 64%) followed by those aged 1-5 years (7 cases; 28%) and the least in dogs over 10 years (2 cases; 8%). Later on, Roopali et al. (2020) [14] also reported that dogs between 6-8 years of age (52.381%) were more prone to hypothyroidism. The increased susceptibility in adult dogs was in agreement with the reports of Kumar et al. (2007) [15] reported that thyroid hormone concentrations are expected to decrease with age and may actually be above adult normal levels in puppies. In the present study, males (9/12) constituted 75.00% of the cases, indicating a higher occurrence of dermatoses associated with hypothyroidism in male dogs as compared to females (3/12; 25.00%) (Table-1). Similarly, Kour et al. (2020) [16] reported that males (74.29%) were more commonly affected than females (25.71%). Later on, Naveen (2024) [17] also reported higher incidence of hypothyroidism in male dogs (70.37%) than females (29.63%). Of total 12 affected dogs, seven were intact males (58.33%), two each of castrated males (16.67%) & intact females (16.67%) and one was a spayed female (8.33%). Including seven intact males and two intact females, a greater proportion of affected dogs were sexually intact (75.00%) as compared to neutered or spayed dogs (25.00%). Similarly, Guglielmini et al. (2019) [18] reported higher relative risk of hypothyroidism in intact males (19/40) dogs followed by spayed female (11/40) and intact females (10/40). The present study showed higher incidence in males and intact dogs than their counter parts. This may be due to the higher representation of male dogs, possibly reflecting pet owners' preference for male dogs (Naveen, 2024) [17] . The higher incidence of dermatoses associated with hypothyroidism in dogs was observed in Labrador Retriever (66.67%) followed by Pomeranian (16.67%), Beagle (08.33%) and German Shepherd (08.33%) (Table-1). Previously, Gulzar et al. (2014) [19] reported a higher prevalence in Labrador Retrievers (14.70%), followed by German Shepherds (15.38%) and Pomeranians (3.57%). Later on, Gupta (2016) [13] also observed the highest incidence in Labrador Retrievers (36%) followed by nondescript dogs (32%), while German Shepherds showed a lower occurrence (8%). Kour et al. (2020) [16] documented that Labrador Retrievers exhibited the highest prevalence (51.43%), followed by Pugs (20.00%) and Samoyeds (8.57%). Lastly, Naveen (2024) [17] also observed a higher incidence in Labrador Retrievers (33.33%) followed by Golden Retrievers and Pomeranians (18.52% each). The higher incidence in Labrador Retrievers may reflect both breed predisposition and their greater population among pet dogs (Raja et al. 2021) [20] . On contrary to our finding of higher incidence of hypothyroidism in Labrador Retriever dogs, Kumar et al. (2007) [15] reported a higher occurrence in Spitz dogs, followed by Labrador Retrievers and German Shepherds. Similarly, Jyothi (2017) [21] also reported higher prevalence in Pomeranians (40.80%), followed by Labrador Retrievers (18.36%). The variability in breed wise distribution across different studies may be attributed to the habitation of different breeds in different regions, breed popularity and sample size (Elgalfy et al., 2025) [7] .

Clinical findings

The major clinical signs observed were alopecia/hair fall (91.67%), bradycardia (83.33%), obesity (75.00%) (Fig. 1), seborrhoea (66.67%) (Fig. 2), pruritus (58.33%), rat-tailed appearance (58.33%) (Fig. 3), failure to hair regrowth (33.33%), inappetence (25.00%), pustules/pyoderma (16.67%) (Fig. 4), hyper-pigmentation (16.67%) and lichenification (16.67%) (Table-2). Earlier, Kumar et al. (2007) [15] reported generalized hair loss in 88% cases followed by "rat tail" appearance (83%), brittle, dry & dull coats (83%), pigmentation and pruritus (27%), obesity (88%), anaemia (33%) and puppy-like coat (22%). Similarly, Gupta (2016) [13] reported alopecia (80%) as predominant clinical signs followed by lethargy (76%), obesity or weight gain (44%), exercise intolerance (24%), poor coat quality (30%), hyper-pigmentation (20%) and "Rat tail" appearance (12%). Lokes-Krupka et al. (2020) [22] also documented the common clinical signs of hypothyroidism including depression, weakness & fatigue (100.0%), symmetrical alopecia (90.9%), anaemia (81.8%), bradycardia & shortness of breath during exercise (72.7%), obesity (63.60%), polydipsia & hypothermia (45.5%) and corneal dystrophy (36.4%). Later on Naveen (2024) [17] reported alopecia either localized or widespread in 74.07% cases followed by "rat tail" appearance (66.67%), obesity (59.26%), lethargy (48.15%), exercise intolerance (44.44%), seborrhoea (40.74%), pyoderma & pruritus (each, 37.04%), lichenification (18.52%), hyperpigmentation (11.11%) and myxoedema & hair regeneration failure (7.41%). In a recent report of Elgalfy et al. (2025) [7] , they classified various clinical findings and found that dermatological manifestations were most prevalent (92.85%), followed by metabolic (46.42%), psychological (42.85%), reproductive (14.28%), neuromuscular (10.71%), gastrointestinal and cardiovascular signs (each 7.14%). Further, they observed non-inflammatory, non-pruritic alopecia, asymmetric hair loss at friction sites, bilateral symmetrical truncal alopecia, patchy alopecia and hyperpigmentation with comedone formation as common cutaneous lesions. Metabolic alterations observed were obesity (46.42%), psychological changes included depression and lethargy (42.85%), reproductive signs were infertility (14.28%), neuromuscular involvement comprised ataxia and hind-limb paresis (10.71%), gastrointestinal signs included vomiting (7.14%) and cardiovascular signs consisted of oedema, cough & exercise intolerance (7.14%). The variation in clinical signs is dependent on thyroid hormone deficiency which alters sebaceous gland function and epidermal maturation, causing abnormal keratinization and oily seborrhoea due to impaired secretion. Reduced thyroid hormones also inhibit hair follicle anagen, resulting in dull, brittle hair, and impair cardiac and neural function through decreased myocardial contractility, adrenergic responsiveness, ATP production and Na⁺/K⁺ pump activity (Elgalfy et al., 2025) [7] .

Dermatological profile

During present study, 3 out 12 dogs (25%) were found positive for presence of either bacterial or fungal isolates. Of which, pyoderma was observed in 2 dogs (16.67%) and Malassezia dermatitis was identified in one dog (8.33%).

Recently, Naveen (2024) [17] reported that 40.74% had concurrent skin disorders in which Pyoderma was observed in 37.04% followed by Malassezia dermatitis (18.52%) and demodectic mange (11.11%). Earlier, Bacterial, fungal or mite infection in hypothyroid dogs had been consistently reported by several authors (Reddy and Sivajothi, 2015; Haritha, 2017; Ko et al., 2018; Ramesh et al., 2018) [24][25][26][27] .

Haemato-biochemical& Hormonal alterations

Among the various haematological parameters, the means of TLC (×10 3 /μl) and neutrophils (%) were significantly higher in dermatoses affected dogs associated with hypothyroidism (14.03±1.97; 73.75±3.15; respectively) as compared to healthy dogs (09.37±5.15; 55.83±1.42, respectively). Whereas, the mean of eosinophils (%) was significantly lower in dermatoses affected dogs associated with hypothyroidism (1.42±0.26) than healthy dogs (6.67±0.49).

Other haematological parameters were varied nonsignificantly between the groups (Table -3). The finding of significant higher value of neutrophils and lower value of eosinophils in affected dogs is in accordance with report of Jyothi (2017) [21] who observed increased neutrophil(%) counts (76.27±1.09) with a concurrent decrease in eosinophils counts (0.53±0.11) in hypothyroid dogs compared to healthy controls (70.09±1.57 and 1.18±0.33, respectively). Neutrophilia in hypothyroid dogs has been consistently reported by several authors (Gupta, 2016; Ramesh et al., 2018; Dhillon et al., 2020) [13,27,29] . Similar to our finding, Naveen (2024) [17] also reported significantly higher TLC (16.05±1.13 ×10 3 /μl) in hypothyroid dogs than healthy dogs. Further, he reported non-significant variation in differential leukocyte counts (neutrophils, lymphocytes, monocytes, and eosinophils) in hypothyroid dogs than healthy dogs with significantly lower (p<0.01), haemoglobin (10.89±0.60 g/dL), packed cell volume (33.79±1.47%) and total erythrocyte count (4.99±0.17×10 6 [30] documented hyper-triglyceridemia (1, 098 mg/dL) and hypercholesterolemia (791 mg/dL) in hypothyroid dogs. Scientists had also reported elevated cholesterol (>250 mg/dL) and triglycerides (>100 mg/dL) in hypothyroid dogs (Gupta, 2016; Jyothi, 2017; Ko et al., 2018; Dhillon et al., 2020) [13,21,26,29] . In context to significant increased value of ALT in in hypothyroid dogs, Naveen (2024) [17] reported documented significantly elevated ALT (77.52±26.05IU/L) [16] . During the study, the means of FT4 and TT4 were found significantly lower in dogs with dermatoses associated with hypothyroidism than healthy dogs (Table -3). Similarly, significantly lower FT4 and TT4 in hypothyroid dogs than healthy dogs were observed previously by scientists (Higgins et al., 2006; Kumar et al., 2007; Reddy and Sivajothi, 2015; Jyothi, 2017) [15,21,24,30] . In a present study, mean value of TSH (µIU/ml) was found comparatively higher (0.222±0.05) in dermatoses affected dogs associated with hypothyroidism than healthy dogs (0.150±0.04) along with significant lower values of FT4 and TT4. In context to higher values of TSH, Kour et al. (2021) [16] reported reduced Total T 4 (0.44±0.61 µg/dL) with elevated TSH (6.79±0.01 ng/mL). While, Mohanambal et al. (2023) [29] and Naveen (2024) [17] reported significantly reduced Total T 4 (0.5 µg/dL), Free T 4 (<0.3 ng/dL), and elevated TSH (2.61 ng/mL). Lowered Free T 4 and Total T 4 in hypothyroid dogs result due to progressive destruction of functional thyroid tissue as a result of lymphocytic thyroiditis or idiopathic thyroid atrophy. Loss of thyroid follicles reduces iodination of thyroglobulin, leading to decreased synthesis and secretion of Total T 4 and Free T 4 . In some cases, reduced circulating thyroid hormones may also be influenced by dysfunction of the hypothalamic-pituitary axis. Impaired secretion of thyroid-stimulating hormone (TSH) from the pituitary, as seen in secondary hypothyroidism, results in inadequate stimulation of the thyroid gland. Similarly, insufficient release of thyrotropinreleasing hormone (TRH) from the hypothalamus can lead to tertiary hypothyroidism (Ettinger et al., 2017) [5] .

Conclusions

Comparatively higher incidences of dermatoses associated with hypothyroidism in dogs were observed in older aged dogs (>6 years), in males and Labrador retriever dogs. Most frequently observed clinical signs in dermatoses affected dogs associated with hypothyroidism were alopecia/hair fall, bradycardia, obesity, seborrhoea, lethargy, rat tailed appearance and pruritus. Dermatoses affected dogs associated with hypothyroidism showed significant increased values of ALT, cholesterol and triglyceride along with significant decreased Free T 4 and Total T 4 value than the healthy dogs.

Acknowledgement

AcknowledgementsThe authors are thankful to Principal, College of Veterinary Science & A. H., KU, Navsari and Head of Department of Veterinary Medicine and Veterinary Clinical Complex for providing necessary facilities to conduct this study.

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