Hemato-biochemical and thyroid profile alterations in dogs with hypothyroidism associated neuromuscular disorders

Introduction

Hypothyroidism is the most common hormonal disorder in dogs, with a global prevalence of 0.20% (Dixon, 2001) [11] and 0.80% (Catherine et al., 2005) [8] and reported rates in India of 0.206% in Mumbai, 0.40% in Hisar, and 0.174% in Punjab (Pawar, 2009; Gulzar et al., 2014, Kour et al., 2020) [32,17,25] . The nervous and endocrine systems jointly regulate body functions, with the former acting quickly through electrical signals and the latter through slower, long-lasting hormonal effects (Vala et al., 2013) [37] . Thyroxine plays a key role in ATP production by enhancing mitochondrial function and ATPase activity, which supports the Na⁺/K⁺ pump critical for axonal transport. In hypothyroidism, reduced ATP and ATPase activity impair this transport, potentially leading to axonal degeneration and peripheral neuropathy (Jaggy et al., 1994) [19] . As a result, hypothyroidism can affect the cranial and peripheral nerves as well as the central nervous system, causing signs such as facial nerve paralysis, megaesophagus, vestibular disease, generalized weakness, proprioceptive deficits, and lower motor neuron dysfunction that may progress to paraparesis or tetraparesis (Lathan, 2012; Ettinger et al., 2000) [28,12] . In India, Radio Immunoassay (RIA) has been widely used for hormone measurement in veterinary clinical settings (Dadke et al., [9,34,15,20,16,35,23] . At Mumbai Veterinary College, the Department of Veterinary Clinical Medicine and Veterinary Nuclear Medicine, along with the radioisotope laboratory, has successfully established reference ranges for canine thyroid hormones, including TT3, TT4, and fT4, using RIA. The study focuses on the hemato-biochemical and thyroid profile alterations in Dogs with hypothyroidism associated neuromuscular disorders.

Materials and Methods

Statutory approval:

The study commenced following approval from the Institutional Ethics Committee for Veterinary Clinical Research (IEC-VCR) and the Institutional Biosafety Committee (IBSC) at Mumbai Veterinary College, MAFSU, Mumbai, India.

Selection of hypothyroid dogs

A total of 28 dogs were included, comprising 7 apparently healthy dogs (Group I) and 21 dogs with suspected hypothyroidism and neuromuscular disorders (Group II). Group II included dogs of various breeds (10 males and 11 females) with a mean age of 6.83 ± 0.68 years and average body weight of 21.26 ± 2.42 kg. These cases were ethically enrolled at the clinical facility of Mumbai Veterinary College for thyroid evaluation.

Hormonal analysis

Blood samples were collected from the cephalic or saphenous veins, and serum was stored at -20°C for hormonal testing. TT3, TT4, and fT4 were measured using commercial human RIA kits (Immunotech, Czech Republic), while canine-specific TSH was assessed using an ELISA kit (Wuhan Fine Biotech Co., Ltd). Hormonal assays were conducted at the Radio Isotope Laboratory, Mumbai Veterinary College, following the manufacturers' protocols. Each sample was tested in duplicate, and quality control checks ensured assay reliability through control sample evaluation and recovery rates.

Diagnosis

Hypothyroidism was diagnosed based on abnormal thyroid hormone levels and clinical improvement following thyroxine supplementation.

Statistical analysis

Data were analyzed using mean and standard error calculations as per Snedecor and Cochran (2004), with additional nonparametric methods applied for result validation.

Results and discussion

The neurological signs recorded in the present study were nystagmus (n=1/ [4] , Jaggy et al. (1994) [19] , Panciera (1994) [31] , and Fracassi and Tamborini (2011) [14] . The mean levels of TT3, TT4, fT4, and TSH in healthy dogs were 1.08 ± 0.14 nmol/L, 20.12 ± 1.40 nmol/L, 14.77 ± 0.83 pmol/L, and 0.25 ± 0.04 ng/mL, respectively. In hypothyroid dogs with neuromuscular disorders, the corresponding mean values were 0.89 ± 0.04 nmol/L for TT3, 9.45 ± 0.94 nmol/L for TT4, 7.72 ± 0.37 pmol/L for fT4, and 1.59 ± 0.20 ng/mL for TSH. In the hypothyroid dogs associated with neuromuscular disorders, the mean concentrations of TT3, TT4, and fT4 were below the reference ranges established by Galdhar et al. (2022) [16] for healthy dogs (Table1). A highly significant (p≤0.01) difference was observed in serum total thyroxine and free thyroxine levels between the groups, while a non-significant difference was found in TT3 concentrations. Similar findings were reported by Higgins et al. (2006) [18] and Alone et al (2025) [1] . The lack of a significant difference in TT3 levels between healthy and hypothyroid dogs supports the observations of Kantrowitz et al. (2001) [22] , who queried about the sensitivity and accuracy of TT3 for diagnosing hypothyroidism. The average TSH level in the hypothyroid group exceeded the reference ranges established for healthy dogs by Kemppainen and Behrend (2001) [24] , Gulzar et al. (2014) [17] , Kaur et al. (2021) [26] , and Boretti et al. (2022) [7] . A significant difference (p≤0.01) was observed between the healthy and hypothyroid groups, with hypothyroid dogs showing elevated TSH concentrations. These findings are consistent with those reported by Bonagura and Twedt (2009) [6] , Pawar (2009) [32] , and Fernandez and Seth (2016) [13] , who also noted significantly increased TSH levels in hypothyroid cases. The Mean ± SE values for hemoglobin, total erythrocyte count, and packed cell volume in healthy dogs in this study were 14.77 ± 0.90 (gm%), 6.55 ± 0.40 (×10 6 /µl), and 43.23 ± 2.63 (%), respectively. In contrast, the mean values for these parameters in hypothyroid dogs were 11.11 ± 0.58 (gm%), 4.80 ± 0.25 (×10 6 /µl), and 32.29 ± 1.71 (%) (Table 1). The study found highly significant (p≤0.01) differences in hemoglobin, total erythrocyte count, and packed cell volume between healthy dogs (Group I) and those with hypothyroidism-associated neuromuscular disorders (Group II). The Mean ± SE values for mean corpuscular volume, mean corpuscular hemoglobin, and mean corpuscular hemoglobin concentration were within the normal reference range. However, the values for hemoglobin and packed cell volume were below the reference range, indicating normocytic, normochromic anemia in the hypothyroid dogs of Group II. These findings are consistent with those of Jaggy et al. (1994) [19] , Kumar et al. (2007) [27] , Blois (2008) [5] , Fracassi and Tamborini (2011) [14] , Romão et al. (2012) [33] , Kour et al. (2021) [26] , and de Oliveira (2022) [7] . Earlier studies by Mooney (2011) [29] , Bertalan et al. (2013) [3] , and Kour et al. (2020) [25] have reported that thyroid hormones stimulate erythropoiesis by promoting the rapid proliferation of immature erythroid progenitors and enhancing erythropoietin (EPO) production through the activation of erythropoietin gene expression. Conversely, Kumar et al. (2007) [27] suggested that bone marrow suppression could be a potential cause of anemia in hypothyroid dogs. The study reported non-significant (p≤0.05) alterations in the leucocyte and platelet counts. The lipid profile, including serum cholesterol, showed significant (p≤0.05) alterations in healthy and hypothyroid groups. The study reported Mean ± SE values of 154.71 ± 17.95 (mg/dl) in healthy dogs and 219.14 ± 13.76 (mg/dl) in hypothyroid dogs (Table 1). This finding is consistent with the work of Kumar et al. (2007) [27] , Vitale and Olby (2007) [38] , Blois et al. (2008) [5] , Pawar (2009) [32] , Fracassi and Tamborini (2011) [14] , Romão et al. (2012) [33] , de Oliveira (2022) [7] , Alone (2024) [2] , and Naveen (2024) [2] . The results of the present study also align with Kahn et al. (2006) [21] , who reported that hypothyroid cases often exhibit cholesterol levels at the upper end of the normal range. These researchers emphasized the role of thyroxine in lipid synthesis, mobilization, and degradation through its effects on hepatic and lipoprotein lipase, as well as its action on hepatic low-density lipoprotein (LDL) receptors. They attributed the observed hypercholesterolemia in hypothyroid dogs to the reduced thyroxine levels associated with the condition. The study reported non-significant (p≤0.05) alterations in liver function test, kidney function tests and serum electrolytes between the groups.

Conclusion

Dogs with hypothyroidism showed significant (p≤0.05) changes in hematological and biochemical parameters, including normocytic normochromic anemia and elevated cholesterol levels. Additionally, they had significantly lower (p≤0.01) serum total and free thyroxine concentrations, while their thyroid-stimulating hormone levels were significantly (p≤0.01) elevated.

Acknowledgement

AcknowledgmentThe authors express gratitude to Maharashtra Animal and Fishery Sciences University-Nagpur (India) and Mumbai Veterinary College, Parel-Mumbai (India) for providing radiation facilities and support for RIA kits for hormonal estimation. The authors also acknowledge the support of the Board of Radiation and Isotope Technology and the Department of Atomic Energy, Govt. of India.

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