Goitrous hypothyroidism associated with treatment with trimethoprim-sulfamethoxazole in a young dog

CASE DESCRIPTION: A 16-week-old female Boxer that had been treated for 5 weeks with trimethoprim-sulfamethoxazole and chloramphenicol because of aspiration pneumonia was evaluated for bilaterally symmetric masses in the subcutaneous tissues of the ventral neck, in the region of the larynx. CLINICAL FINDINGS: Fine-needle aspirates were obtained from the neck masses; cytologic examination revealed well-differentiated thyroid epithelial tissue. A blood sample was collected for serum biochemical and thyroid function analyses. Mild hyperphosphatemia, severe hypercholesterolemia, mild hyperkalemia, and a mild increase in creatine kinase activity were identified. Serum concentration of total thyroxine was less than the lower reference limit, and that of thyroid-stimulating hormone was greater than the upper reference limit. Findings were consistent with a diagnosis of clinical hypothyroidism in a skeletally immature dog. TREATMENT AND OUTCOME: Treatment with trimethoprim-sulfamethoxazole was discontinued. The dog was reevaluated 3 weeks later, at which time the neck masses were markedly decreased in size. Serum concentrations of cholesterol and potassium were lower; serum concentrations of total thyroxine and thyroid-stimulating hormone were near or within respective reference ranges. Age-appropriate increases in serum phosphorus concentration and serum alkaline phosphatase activity were also detected. CLINICAL RELEVANCE: To the authors' knowledge, this is the first report of antimicrobial-induced goiter in a dog. Cytologic examination of fine-needle aspirates and interpretation of data from serum biochemical and thyroid function analyses were needed to obtain a definitive diagnosis. Practitioners should include goiter among the differential diagnoses for ventral neck swellings in young dogs receiving potentiated sulfonamide antimicrobials.     

The response of the pituitary-adrenal and pituitary-thyroidal axes to the plasma glucose perturbations in Babesia canis rossi babesiosis

This prospective, cross-sectional, interventional study was designed to determine the association between the hormones of the pituitary-adrenal and pituitary-thyroid axes and other clinical parameters with the blood glucose perturbations in dogs with naturally occurring Babesia canis rossi babesiosis. Thirty-six dogs with canine babesiosis were studied. Blood samples were obtained from the jugular vein in each dog prior to treatment at admission to hospital and serum endogenous adrenocorticotrophic hormone (ACTH), pre-ACTH cortisol, thyroxine, free thyroxine and TSH concentrations were measured. Immediately thereafter each dog was injected intravenously with 5 microg/kg of ACTH (tetracosactrin). A 2nd blood sample was taken 1 hour later for serum post-ACTH cortisol measurement. Three patient groups were recruited: hypoglycaemic dogs (glucose < 3.3 mmol/l, n = 12); normoglycaemic dogs (glucose 3.3-5.5 mmol/l, n = 12); hyperglycaemic dogs (glucose > 5.5 mmol/l, n = 12). Basal and post-ACTH serum cortisol concentrations were significantly higher in hypoglycaemic dogs, whereas body temperature, serum thyroxine and free thyroxine were significantly lower in hypoglycaemic dogs. Haematocrit was significantly lower in both hypo-and hyperglycaemic dogs compared with normoglycaemic dogs. Low blood glucose concentrations were significantly associated with high basal and post-ACTH cortisol concentrations and with low serum thyroxine and free thyroxine concentrations in dogs suffering from B. canis rossi babesiosis.     

Radioactive Iodine Treatment of a Functional Thyroid Carcinoma Producing Hyperthyroidism in a Dog

Radioactive iodine (131I) was used in the treatment of a 12-year-old female dog with hyperthyroidism resulting from a large, unresectable (and metastatic) thyroid carcinoma associated with signs of severe inspiratory stridor and dyspnea. Hyperthyroidism was diagnosed on the basis of clinical signs (polyuria, polydipsia, polyphagia, weight loss, nervousness) and high basal serum thyroxine (T4) concentrations, as well as thyroid radioiodine kinetic studies that showed a high radioiodine uptake into the thyroid (% thyroid uptake) and markedly increased serum concentrations of protein-bound iodine-131 (PB131I) after 131I tracer injection. Thyroid imaging revealed diffuse radionuclide accumulation by the tumor, which involved both thyroid lobes. The dog was treated with three large doses of radioiodine (131I), ranging from 60 to 75 mCi, given at intervals of 5 to 7 months. The dog became euthyroid, and the size of the tumor decreased by approximately 25% after each 131I treatment, improving the severe inspiratory stridor and dyspnea, but both the hyperthyroid state and breathing difficulty recurred within a few months of each treatment. The dog was euthanatized 5 months after the last treatment because of progressive tracheal compression and pulmonary metastasis.     

Acromegaly due to a somatroph adenoma in a dog

A 10-year-old uncastrated male Dalmatian dog was referred for gait abnormalities consisting of chronic progressive stiffness and rigidity. Other symptoms were polyphagia associated with weight gain, polyuria and polydipsia, excessive panting, and an inspiratory stridor. The owner had noticed progressive thickening of the skin and enlargement of the tongue over the last 3 years. Physical examination revealed thickening of the skin, redundant skin folds, and enlargement of the tongue. The only remarkable abnormalities found on routine laboratory examination were mild anaemia and an increased serum fructosamine concentration. Circulating concentrations of total thyroxine, free thyroxine, and cTSH, and the results of an ACTH stimulation test were all within reference ranges. The basal serum growth hormone (GH) concentration was markedly elevated (23microg/l) and did not decrease during a glucose tolerance test or after somatostatin administration. The serum insulin-like growth factor-1 concentration was also markedly elevated (1254microg/l). Basal serum insulin concentration was high (95mU/l) and insulin concentrations increased considerably after glucose loading, consistent with insulin resistance. Abdominal ultrasonography showed no abnormalities. Survey radiographs of the vertebral column showed severe spondylosis deformans extending from the cervical to the lumbosacral spine. CT scanning of the skull showed an enlarged pituitary gland with normal enhancement pattern. On post-mortem examination, the entire vertebral column appeared as a single and inflexible structure due to the presence of multiple fused osteophytes. The pituitary gland contained an acidophilic adenoma that immunostained positively for GH (and negatively for ACTH and alpha-MSH). In conclusion, this Dalmatian dog with acromegaly and insulin resistance represents the first case of GH hypersecretion proven to be due to a somatotroph adenoma.     

Effects of administration of a low dose of frozen thyrotropin on serum total thyroxine concentrations in clinically normal dogs.

Thyroid function was evaluated in 18 healthy dogs by thyrotropin (TSH) stimulation. Two dose regimens were used in each dog: 0.1 IU/kg body weight of freshly reconstituted lyophilized TSH and 1 IU/dog of previously frozen and stored TSH (up to 200 days), both given intravenously. Blood samples were collected prior to and at four and six hours after TSH administration. Serum was evaluated for total thyroxine concentrations by radioimmunoassay. All dogs were classified as euthyroid on the basis of response to 0.1 IU/kg body weight of freshly reconstituted TSH at four and six hours. The 1 IU dose of TSH, previously frozen for up to 200 days, induced increases in serum total thyroxine concentration over baseline at four and six hours that were not significantly different from those resulting from the use of the higher dose of fresh TSH. In all test groups, there were no statistically significant differences between total thyroxine concentrations at four and six hours post-TSH administration. It was concluded that an adequate TSH response can be achieved with the use of 1 IU of TSH/dog for clinically normal dogs between 29.0 kg and 41.6 kg body weight, even if this TSH has been frozen at -20 degrees C for up to 200 days. Further, blood collection can be performed at any time between four and six hours. Similar studies are needed to evaluate this new protocol in hypothyroid dogs and euthyroid dogs suffering nonthyroidal systemic diseases.     

Congenital hypothyroidism in a boxer dog

Congenital central hypothyroidism was diagnosed in a one-year-old boxer dog. The dog was presented for investigation of lameness, lethargy and obesity. Survey skeletal radiographs revealed delayed bone maturation and epiphyseal dysgenesis. A diagnosis of hypothyroidism was confirmed on the basis of a low basal serum thyroxine (T₄) concentration that failed to increase following bovine thyroid stimulating hormone (TSH) administration. However, repeated administration of TSH resulted in reactivation of the thyroid gland suggesting a central rather than a primary problem. Consistently low basal plasma Cortisol concentrations were suggestive of a concurrent secondary or tertiary hypoadrenocorticism. Surprisingly, plasma growth hormone concentrations were elevated before treatment but decreased once thyroid replacement therapy had commenced.     

Serum cortisol and thyroxine concentrations as predictors of death in critically ill puppies with parvoviral diarrhea

OBJECTIVE: To evaluate the role of adrenal and thyroid hormones in the prediction of death in a population of critically ill puppies with parvoviral diarrhea by measuring serial daily serum concentrations of cortisol and thyroxine. DESIGN: Prospective case-control study. ANIMALS: 57 critically ill puppies with parvoviral diarrhea admitted to the hospital and 17 clinically normal control puppies. PROCEDURES: Basal serum cortisol and thyroxine concentrations were measured for each dog with parvoviral diarrhea at admission (prior to treatment) and daily until death, euthanasia, or discharge. RESULTS: Median time between admission and death was 48 hours (ie, on day 3). Median serum cortisol concentration on day 1 (admission) in all dogs with parvoviral diarrhea (248 nmol/L) was significantly higher than in control dogs (77 nmol/L). No significant difference was found in the day 1 median serum cortisol concentration of 11 dogs that died (302 nmol/L) and 46 dogs that survived (238 nmol/L). A significantly higher median serum cortisol concentration was, however, found in nonsurvivor group dogs, compared with survivor group dogs, on days 2 and 3. Median serum thyroxine concentration on day 1 in dogs with parvoviral diarrhea was significantly lower than in control dogs (8.12 nmol/L vs 35 nmol/L, respectively). Median serum thyroxine concentration of nonsurvivor group dogs (4.4 nmol/L) was significantly lower than that of survivor group dogs (9.2 nmol/L) at admission and became even lower on days 2 and 3. CONCLUSIONS AND CLINICAL RELEVANCE: High serum cortisol and low serum thyroxine concentrations at 24 and 48 hours after admission were associated with death in dogs with parvoviral diarrhea.     

Diagnosis of canine claw disease – a prospective study of 24 dogs

The aetiology of claw disease in 24 dogs exhibiting only claw disease was investigated with cytologic examination of claw exudate, complete blood count (CBC), serum biochemistry panel, urinalysis, total thyroxine (tT4) concentration, antinuclear antibody (ANA) titre, bacterial culture and sensitivity testing, fungal culture, histopathology of claw biopsy samples and elimination diet. Abnormalities on the CBC, serum biochemistry panel and urinalysis were minor and nonspecific. Total T4 concentrations were within the normal laboratory reference range. Fungal cultures and ANA titres were negative in all dogs. A bacterial infection was present in approximately half of the dogs. On histological examination of claw tissue, a cell-poor or cell-rich interface onychitis was seen in all but one dog. Evidence for an adverse reaction to food was present in four dogs. One dog responded completely to antibiotic therapy. Interface onychitis seems to be a histological reaction pattern of the claw matrix in the dog with various possible underlying aetiologies. In dogs with claw disease as the only clinical sign, the recommended initial diagnostic evaluation includes cytologic examination, bacterial culture and sensitivity, claw biopsy and an elimination diet.     

Acute overdose of levothyroxine in a dog.

An overdose of up to 850 levothyroxine sodium tablets (0.2 mg) in a healthy 6-year-old 16.8-kg dog induced an episode of vomiting and hippus within 9 hours of ingestion. The dog was treated with activated charcoal and saline (magnesium sulfate) cathartic. Initially the serum concentration of thyroxine (T4) 4,900.9 nmol/L. On the second day, serum concentration of triiodothyronine (T3) was 5.3 nmol/L. Serum T4 concentration decreased slowly and was not determined to be normal until day 36. Serum T3 concentration was found to be normal on day 6. Serum alanine transaminase activity peaked on day 6 at 345 U/L. Significant abnormalities were not found during the following 36 days. Clinical signs of thyroid hormone toxicosis in dogs and cats include hyperactivity, lethargy, tachycardia, tachypnea, dyspnea, abnormal pupillary light reflexes, vomiting, and diarrhea. High overdoses of levothyroxine sodium in dogs should be managed by initial decontamination and administration of activated charcoal with a cathartic followed by supportive care.     

Primary anestrus due to dietary hyperthyroidism in a miniature pinscher bitch

A 2-year-old intact miniature pinscher bitch that had been on a bones and raw foods diet since birth showed no signs of estrus despite a 40-day course of cabergoline. Elevated levels of thyroxine were detected in the serum (51 nmol/L) and in the juice of the meat (183 nmol/L) fed to the dog. Change in diet and treatment with oral cabergoline resulted in signs of proestrus in 13 d, pregnancy, and normal birth of 5 puppies.     

Biological variation of canine serum thyrotropin (TSH) concentration

The aim of the present study was to estimate the between-dog, within-dog and analytical components of variance for serum thyrotropin (TSH) in healthy dogs, and to use these components of variance to 1) estimate the critical difference for significance between serial results; 2) assess the utility of the conventional population-based reference interval; 3) set a desirable performance standard for analytical imprecision; and 4) estimate the number of samples required for determination of the true mean value for an individual dog. Using the Immulite test system, TSH was measured in serum samples collected weekly for five weeks from eight clinically healthy dogs. Results were subjected to nested analysis of variance. Between-dog variation was 43.6%, within-dog variation was 13.6%, analytical variation was 8.8%, the one-sided critical difference was 37.8%, the index of individuality was 0.4, the maximum allowable analytical imprecision was 6.8%, and the number of samples required to determine the true mean value in a single dog was 40. In practical terms, the present study indicated that the analytical imprecision of canine serum TSH measurement should be < 7%, and that comparing a single serum TSH measurement from an individual dog to the conventional population-based reference range may be too insensitive to detect small but important changes in the serum TSH level of that particular dog. In addition, when treating a hypothyroid dog, serum TSH, measured on a weekly basis, should decrease by at least one-third before any effect of exogenous thyroxine supplementation can be said to have influenced the serum TSH level.     

Abnormal canine triiodothyronine-binding factor characterized as a possible triiodothyronine autoantibody

Of more than 6,000 canine serum samples submitted to the Endocrine Diagnostic Laboratory of the School of Veterinary Medicine, Auburn University, Ala, for thyroid evaluation in 1983, 18 contained an abnormal triiodothyronine (T3)-binding factor (T3BF). These samples were easily distinguished from non-T3BF containing samples because the factor interfered with the radioimmunoassay for total T3 resulting in a profound increase in apparent values for T3 concentration. Most of the T3BF-containing samples did not have unusual thyroxine binding or inappropriate thyroxine concentrations. Triiodothyronine binding in samples containing T3BF was inhibited by addition of exogenous T3 and was, with one exception, not affected by the addition of 8-anilino-1-naphthalene sulfonic acid (ANS). Apparent affinity constants determined by Scatchard analysis were considerably greater than those of circulating T3-binding proteins found in human beings, but were similar to values obtained for human T3 autoantibodies. After the addition and incubation of [125I] T3 with T3BF-containing samples, a large fraction of the radioactivity bound by T3BF could be precipitated by the addition of goat antibody to dog immunoglobulin G. Additional observations that the binding was insensitive to inhibition by ANS, was resistant to heat inactivation, and had a high apparent affinity constant for T3 were consistent with the idea that the factor was an autoantibody to T3.     

Comparison of thyroid analytes in dogs aggressive to familiar people and in non-aggressive dogs

A cross-sectional study was performed in order to examine the association between canine aggression to familiar people and serum concentrations of total thyroxine (TT4), free thyroxine (fT4), thyroxine autoantibodies (T4AA), total triiodothyronine (TT3), free triiodothyronine (fT3), triiodothyronine autoantibodies (T3AA), thyroid stimulating hormone (TSH), and thyroglobulin autoantibodies (TgAA). The subjects were 31 dogs historically aggressive to familiar people and 31 dogs with no history of aggression. Behavioral evaluation and physical examination were completed for each dog in addition to a complete blood count, serum chemistry panel, TT4, fT4 by equilibrium dialysis, TT3, fT3, TgAA, T3AA, and T4AA. Significant differences were found between the two groups with respect to only T4AA, which was increased in the aggressive group, but the concentrations for both groups were within the normal reference range. There were no differences between the two groups in the thyroid analytes most commonly measured by veterinary practitioners evaluating thyroid function in dogs. The results of this study revealed no significant difference between aggressive and non-aggressive dogs in the thyroid concentrations most commonly used to diagnose canine hypothyroidism.     

Polyglandular deficiency syndrome in a boxer dog: Thyroid hormone and glucocorticoid deficiency

Summary

Primary hypothyroidism and partial primary adrenocortical deficiency (isolated glucocorticoid deficiency) were diagnosed in an 8‐year‐old spayed female boxer dog, presented because of progressive symmetrical truncal alopecia, lethargy, and intolerance to cold. The diagnosis was based upon the combination of low, non‐TSH‐responsive concentrations of plasma thyroxine and low urinary excretion of corticoids together with high plasma concentrations of ACTH. Normal suppressibility of ACTH concentrations by a low dose of dexamethasone indicated an intact feedback system. Plasma growth hormone levels were elevated, most probably because somatostatin release was depressed by the glucocorticoid deficiency.

The dog improved during oral replacement therapy with thyroxine until death ensued after 9 months as a result of intercurrent disease. Autopsy revealed thyroid atrophy and lymphocytic adrenalitis with complete destruction of the zona fasciculata and zona reticularis of the adrenal cortex.

The combination of primary hypothyroidism and primary adrenocortical deficiency in this dog is identical to the entity known as type II polyglandular autoimmunity or Schmidt's syndrome in humans. The adrenocortical insufficiency remained confined to glucocorticoid deficiency during the observation period; on no occasion did electrolyte concentrations in the plasma reach values suggestive of mineralocorticoid deficiency.     

Effects of hyperlipemia on radioimmunoassays for progesterone, testosterone, thyroxine, and cortisol in serum and plasma samples from dogs

Hyperlipemic serum and plasma samples often are received by clinical laboratories for endocrinologic analysis by radioimmunoassay. We designed a study to determine what effect, if any, hyperlipemia has on estimation of lipid-soluble hormone concentrations determined by solid-phase radioimmunoassays. Progesterone, testosterone, thyroxine, and cortisol concentrations were determined in canine plasma and serum with various degrees of lipemia. Samples of serum, heparinized plasma, and EDTA-treated plasma were obtained from blood collected from 4 female and 4 male Beagles by use of evacuated tubes. To induce hyperlipemia in vitro, IV fat emulsion was diluted in deionized water to produce 0 (water only), 33, 67, or 100% mixtures. Twenty microliters of each mixture then was added to the subsamples of serum and plasma from each dog. Hormone concentrations were determined, using validated radioimmunoassays. Triglyceride concentrations were determined by enzymatic assay. Addition of IV fat emulsion in vitro was an accurate and reproducible means of altering triglyceride concentrations in the samples. Triglyceride concentrations as high as 700 mg/dl had no effect on radioimmunoassays for progesterone, testosterone, and thyroxine in serum, heparinized plasma, or EDTA-treated plasma. Addition of 100% (but not 33 or 67%) fat emulsion reduced the mean cortisol concentration in heparinized plasma by 12% (P less than 0.05). This severe hyperlipemia did not affect quantification of cortisol in serum or EDTA-treated plasma.     

Serum concentrations of thyroxine and 3,5,3'-triiodothyronine in dogs before and after administration of freshly reconstituted or previously frozen thyrotropin-releasing hormone

Concentrations of serum thyroxine (T4) and 3,5,3'-triiodothyronine (T3) were determined after the administration of freshly reconstituted thyrotropin-releasing hormone (TRH), reconstituted TRH that had been previously frozen, or thyrotropin (TSH) to 10 mature dogs (6 Greyhounds and 4 mixed-breed dogs). Thyrotropin-releasing hormone (0.1 mg/kg) or TSH (5 U/dog) was administered IV; venous blood samples were collected before and 6 hours after administration of TRH or TSH. Concentrations of the T4 and T3 were similar (P greater than 0.05) in serum after administration of freshly reconstituted or previously frozen TRH, indicating that TRH can be frozen at -20 C for at least 1 week without a loss in potency. Concentrations of T4, but not T3, were higher after the administration of TSH than they were after the administration of TRH (P less than 0.01). Concentrations of T4 increased at least 3-fold in all 10 dogs given TSH, whereas a 3-fold increase occurred in 7 of 10 dogs given freshly reconstituted or previously frozen TRH. Concentrations of T4 did not double in 1 dog given freshly reconstituted TRH and in 1 dog given previously frozen TRH. Concentrations of T3 doubled in 5 of 10, 2 of 10, and 5 of 10 dogs given TSH, freshly reconstituted TRH, or previously frozen TRH, respectively. Results suggested that concentrations of serum T4 are higher 6 hours after the administration of TSH than after administration of TRH, using dosage regimens of 5 U of TSH/dog or 0.1 mg of TRH/kg.(ABSTRACT TRUNCATED AT 250 WORDS)     

Dietary hyperthyroidism in dogs

Objectives: Evaluation of dogs with elevated plasma thyroxine concentration fed raw food before and after changing the diet. Method: Between 2006 and 2011 all dogs presented with an elevated plasma thyroxine concentration and a dietary history of feeding raw food were included. Thyroxine (reference interval: 19·3 to 51·5 nmol/L) and in many cases also thyroid-stimulating hormone concentrations (reference interval: <0·30 ng/mL) were measured initially and after changing the diet. Results: Twelve dogs were presented with a median age of five years. The median plasma thyroxine concentration was 156·1 (range of 79·7 to 391·9) nmol/L; in six dogs, thyroid-stimulating hormone concentration was measured and was <0·03 ng/mL in five dogs and 0·05 ng/mL in one dog. Six dogs showed clinical signs such as weight loss, aggressiveness, tachycardia, panting and restlessness while six dogs had no clinical signs. After changing the diet eight dogs were examined: thyroxine concentration normalised in all dogs and clinical signs resolved. Clinical Significance: Dietary hyperthyroidism can be seen in dogs on a raw meat diet or fed fresh or dried gullets. Increased plasma thyroxine concentration in a dog, either with or without signs of hyperthyroidism, should prompt the veterinarian to obtain a thorough dietary history.     

Effect of oral administration of sulfadiazine and trimethoprim in combination on thyroid function in dogs.

The effect of oral administration of sulfadiazine and trimethoprim in combination on serum concentrations of thyroxine (T4), triiodothyronine (T3) and free thyroxine (fT4) and the thyroid hormone response to thyrotropin administration was assessed. Six dogs were administered sulfadiazine (12.5 mg/kg) and trimethoprim (2.5 mg/kg) orally for 28 days; six untreated dogs acted as controls. Serum T4, T3 and fT4 were determined weekly during and for four weeks after treatment. Thyrotropin response tests were performed prior to treatment, after four weeks of treatment and three weeks after stopping treatment. There were no significant differences in mean serum T4, T3 or fT4 concentrations between treated and control groups at any time during the study. Mean concentration of serum T4 over time did not differ significantly from baseline concentration in either group. Significant differences in the mean serum T3 and fT4 concentrations occurred at several time points in treatment and control groups, and were apparently unrelated to treatment. Significant differences in the T4 or T3 response to thyrotropin administration within or between groups were not present. Serum T3 and fT4 concentrations fluctuate in normal dogs. Administration of sulfadiazine and trimethoprim in combination does not affect tests of thyroid function in the dog.     

Hypercalcaemia in a dog with primary hypothyroidism

A 7-year-old female beagle was evaluated for symptomatic hypercalcaemia and primary hypothyroidism. Clinical findings were typical for hypothyroidism. Plasma parathyroid hormone was low and obvious causes for the hypercalcaemia were ruled out by means of abdominal ultrasonography, ultrasonography of the parathyroid glands, survey thoracic radiographs, and fine needle aspirate cytology of the spleen, liver, and peripheral lymph nodes. Treatment with thyroxine resulted in resolution of the hypercalcaemia after approximately 9 weeks of therapy. This is the 1st report of primary adult-onset hypothyroidism associated with symptomatic hypercalcaemia in a dog.     

Adult-onset demodicosis in two dogs due to Demodex canis and a short-tailed demodectic mite

Infestation with a short-tailed demodectic mite and Demodex canis was diagnosed in both a six-and-a-half-year-old and a four-year-old dog. The clinical picture was compatible with generalised demodicosis complicated by staphylococcal pyoderma (case 1), or localised demodicosis (case 2). In both cases, the short-tailed demodectic mite outnumbered D canis in superficial skin scrapings. The laboratory findings (lymphopenia, eosinopenia, increased serum alkaline phosphatase and alanine aminotransferase activities, diluted urine and proteinuria) and the results of a low dose dexamethasone suppression test were suggestive of underlying hyperadrenocorticism in the first case. Hypothyroidism was considered a possibility in the second case, owing to the sustained bradycardia and the extremely low basal total thyroxine value. Systemic treatment with ivermectin and cephalexin (case 1), or topical application of an amitraz solution in mineral oil, along with sodium levothyroxine replacement therapy (case 2), resulted in a complete resolution of the skin lesions and the disappearance of both types of demodectic mite after two and one and a half months, respectively.