Hypothyroidism in dogs as a baseline of different clinical signs and laboratory results

Abstract

Introduction: Hypothyroidism is the most common endocrinopathy in dogs. It is clinical condition with decrease serum level concentration of thyroid hormones, resulting with different clinical signs. As a common subclinical and clinical condition, hypothyroidism can be congenital and acquired, as well as primary, secondary and tertiary (the last mentioned is very rare). This clinical condition is sometimes hard for diagnosis, but it is very easy for treatment. Aims: The main purpose of this clinical study is interpretation of serum concentration of fT4 in correlation with other laboratory findings (hematology and biochemistry) and clinical manifestation. For that purposes 5 clinical cases will be describe with history data, clinical manifestation and laboratory findings such as clinical condition after treatment protocol. Material and methods: Clinical research was performed in 5 clinical cases admitted in the University clinic. According anamnestic data from the owners, dogs presented different clinical signs, reported at the personal files of the patients. Hematology was performed immediately after sampling on veterinary hematology analyzer Exigo (Sweden), as well as biochemistry status: enzyme serum concentration (ALT, AST, ALKP), degradation profile (urea and creatinine), protein status (albumin, total protein), lipid parameters (cholesterol, triglycerides), according manufacture instruction (Human, Germany) with colorimetric procedure on automatized analyzer Chem Well 2910 (USA). Cytology (Diff Quick staining) was performed only in cases with dermatological lesions. ELISA laboratory method was used for measurement serum concentration of free thyroxin (fT4), on BDLS ELISA reader. Results and Discussion: First case was 6 year female mix breed neutered dog, with progressive skin lesion with hyperpigmentation and episodes of epileptiphormic seizures. Hematology presented mild normocytic, normochromic anemia (5.09 1012/L), and biochemistry results presented only mild increase of ALT (69 U/L) and mild hyperlipidemia (cholesterol 6.89 mmol/l and triglycerides 2.05 mmol/l). Anticonvulsive therapy protocol (phenobarbital 1mg/kg) was not responsive, epileptiformic seizures continue with the same frequency. Cytology finding show non-pruritic non-inflammatory alopecia, with low cellularity of superficial cornified epithelial cells. Serum level concentration fT4 presentedsevere hypothyroidism of 0.29 ng/dl. Initial treatment with levothyroxine started with 10 μcg/kg BID and after one month the treatment dose was increased of 22 μcg/kg BID. Clinical signs of epileptiformic seizures disappeared and laboratory findings corrected within reference ranges. Skin lesions recurrence in irregular intervals. After 5 years of treatment the patient developed hepatic fibrosis. Second case was 5 year male Samoyed, with no specific clinical signs only with polyphagia and increased body condition score. Laboratory finding presented only moderate elevation of degradation profile (urea 18.24 mmol/l and creatinine 174.54 μmol/l). Renal supportive and protective protocol combined with intravenous fluid crystalloid therapy did not give satisfactory results. Serum concentration of fT4 (0.51 ng/dl) show moderate decrease level. Initial treatment with levothyroxine 15 μcg/kg BID give satisfactory results with correction of degradation profile, regular appetite and normal body condition score. Third case was 10 year female Maltese, with history of chronic caught, collapse trachea, intolerance of physical exercise and congestive heart failure with mitral dysplasia. Cardiotonic (0.25 mg/kg pimobendan BID) and diuretic (2 mg/kg furosemide and spironolactone 1 mg/kg SID) treatment was not completely effective protocol, didn’t give satisfactory results. There were intermittent remission of subcutaneous myxedema. Serum concentration of fT4 (0.34 ng/dl) presented marked hypothyroidism. There is no evident dermatology lesions or alterations in laboratory results. Initial treatment of levotiroxine in dose of 22 μcg/kg BID give satisfactory results. Fourth case is a 4 year male cocker spaniel presented marked dermatology clinical signs with symmetric bilateral alopecia, “rat tail” and superficial exfoliate dermatitis. Cytology findings present low cellularity of epithelial cells, intact inflammatory cells predominant neutrophils, less small lymphocytes and telogen defluxion of hair. Dermatology cosmetically products, topically used, was not effective treatment. Biochemistry lipid parameters (hypercholesterolemia 7.15 mmol/l and hypertriglyceridemia 2.84 mmol/l) were indicators for measurement of fT4. Moderate serum concentration of 0.54 ng/dl indicate hypothyroidism. Treatment protocol of levothyroxine 15 μcg/kg BID together with dermal supportive supplements give better condition of the skin and normal values of the lipid parameters. Fifth case: 5 year male Labrador retriever, with bradycardia, myxedema, seborrhea sicca, obtain laboratory results have shown increase serum level of ALT (105.3 U/L). Unclear clinical symptoms and elevated ALT were suspected indicators for hypothyroidism. Serum concentration of fT4 of 0.61 ng/dl confirm diagnosis. Treatment with levothyroxine 20 μcg/kg BID improve better condition of the patient. Conclusion: Decreased serum concentration of fT4 can be used as baseline of many different clinical conditions, non-responsive of regular conventional protocols. Clinical and subclinical hypothyroidism correlated with the degree of clinical manifestation and altered laboratory results.