Electrocardiographic assessment of hyperkalemia in dogs and cats

Objective: To determine if electrocardiogram (ECG) changes induced by hyperkalemia in clinical patients correspond with previously reported changes in experimental animals. Design: Prospective clinical study. Setting: Two private practice 24‐hour emergency and critical care facilities. Animals: Fifteen dogs and 22 cats with serum potassium levels >5.5 mEq/L. Interventions: None. Measurements: The following data were collected when hyperkalemia was documented: ECG (n=37), sodium and chloride (mEq/L) (n=35), total magnesium (mg/dL) (n=18), total calcium (mg/dL) (n=30), and venous pH (n=18). Animals were divided into five groups based on severity of hyperkalemia and ECG interpretation included rate, rhythm and P‐QRS‐T evaluation. Main Results: Twenty‐two of 37 (59%) of the ECGs were normal or revealed abnormalities that have not been previously described in conjunction with hyperkalemia. In dogs, there was no correlation (r=0) between potassium blood levels and heart rate (n=15). There was weak correlation (r=0.40; P=0.06) between potassium blood levels and heart rate in cats (n=22). The correlation was stronger (r=0.64; P<0.05) when data were compared in cats with serum potassium level >8.5 mEq/L (Groups 4 and Group 5; n=11). Conclusions: ECGs obtained from ill dogs and cats with hyperkalemia are inconsistent with ECGs from experimentally induced hyperkalemia. It is difficult to determine the clinical relevance of heart rate differences between cats with serum potassium levels >8.5 mEq/L and animals with experimentally induced hyperkalemia; this may be due to the presence of other biochemical abnormalities in diseased animals.     

Combined hyponatremia and hyperkalemia mimicking acute hypoadrenocorticism in three pregnant dogs

Differential diagnoses for hyponatremia with concurrent hyperkalemia should include hypoadrenocorticism. Renal failure, chylothorax, and gastrointestinal tract disorders may also cause abnormally low serum sodium:potassium ratios. The ACTH stimulation test is the gold standard for diagnosis of hypoadrenocorticism.     

Detection of autoantibodies against thyroid peroxidase in serum samples of hypothyroid dogs

OBJECTIVE: To establish a sensitive test for the detection of autoantibodies against thyroid peroxidase (TPO) in canine serum samples. SAMPLE POPULATION: 365 serum samples from dogs with hypothyroidism as determined on the basis of serum concentrations of total and free triiodothyronine (T3), total and free thyroxine (T4), and thyroid-stimulating hormone, of which 195 (53%) had positive results for at least 1 of 3 thyroid autoantibodies (against thyroglobulin [Tg], T4, or T3) and serum samples from 28 healthy dogs (control samples). PROCEDURE: TPO was purified from canine thyroid glands by extraction with detergents, ultracentrifugation, and precipitation with ammonium sulfate. Screening for anti-TPO autoantibodies in canine sera was performed by use of an immunoblot assay. Thyroid extract containing TPO was separated electrophoretically, blotted, and probed with canine sera. Alkaline phosphatase-conjugated rabbit anti-dog IgG was used for detection of bound antibodies. RESULTS: TPO bands were observed at 110, 100, and 40 kd. Anti-TPO autoantibodies against the 40-kd fragment were detected in 33 (17%) sera of dogs with positive results for anti-Tg, anti-T4, or anti-T3 autoantibodies but not in sera of hypothyroid dogs without these autoantibodies or in sera of healthy dogs. CONCLUSIONS AND CLINICAL RELEVANCE: The immunoblot assay was a sensitive and specific method for the detection of autoantibodies because it also provided information about the antigen. Anti-TPO autoantibodies were clearly detected in a fraction of hypothyroid dogs. The value of anti-TPO autoantibodies for use in early diagnosis of animals with thyroid gland diseases should be evaluated in additional studies.     

ERG findings in three hypothyroid adult dogs with and without levothyroxine treatment

Purpose To evaluate the effects of levothyroxine (LTh) on the electroretinogram (ERG) of adult dogs. Material and methods Binocular, full field photopic and scotopic ERGs were recorded from an anesthetized Maltese Bichon cross (MB), a Yorkshire Terrier (YT) and a Shetland Sheepdog (SS) affected with hypothyroidism and treated with a daily dose of LTh at 20 µg/kg. The photopic ERGs were evoked to 12 different intensities ranging from 0.81 to –2.19 log cd.s/m² and presented under photopic conditions in order to assess (from the derived luminance-response curves) Vmax and b : a amplitude ratio parameters. Photopic flicker ERGs were obtained at 30 Hz. The scotopic ERGs (intensity: –3.09 log cd.s/m²) were recorded while the retina was dark-adapting and after 32 min of dark adaptation. This procedure was performed on two separate sessions: following a 3-day interruption of LTh treatment (S1) and following 30 days without interruption of LTh treatment (S2). Results The mean photopic a-wave peak times were 9.8 ms at S1 and 5.0 ms at S2, respectively. The mean photopic b-wave peak times were 23.3 ms at S1 and 11.5 ms at S2, respectively, and the mean scotopic b-wave peak times (after 32 min of dark adaptation) were 45.2 ms at S1 and 26.0 ms at S2, respectively. No other significant ERG changes were observed. Conclusion Our results indicate that a dose of 20 µg/kg of LTh given to adult dogs was accompanied by a marked peak time shortening of both photopic and scotopic ERGs, without affecting other ERG parameters.     

Retrospective evaluation of acute hyperkalemia of unknown origin during general anesthesia in dogs

ObjectiveTo report and characterize cases of acute hyperkalemia of unknown origin in dogs under anesthesia.Study designMulticentric retrospective clinical study.AnimalsMedical records of 19 client-owned dogs that developed acute hyperkalemia during anesthesia.MethodsAnesthetic records of dogs developing acute hyperkalemia from January 2015 to December 2022 were evaluated. Data collected included demographics, duration of anesthesia until the episode, electrolytes and blood gas measurements, electrocardiogram (ECG) abnormalities, drugs used as part of the anesthetic protocol, hyperkalemia treatment and outcome.ResultsA total of 13 cases met the inclusion criteria with documented acute hyperkalemia with no apparent underlying cause during anesthesia. Dogs were [mean ± standard deviation (range)] 6.5 ± 5.0 (3–10) years old and weighed 18.0 ± 14.3 (5.1–40.0) kg. All dogs were administered dexmedetomidine and an opioid as part of the premedication. All dogs had inhalation anesthesia of >60 minutes’ duration. The first clinical sign was bradycardia that was minimally responsive to anticholinergic administration and was often accompanied by moderate/severe hypotension. These signs were rapidly followed by ECG changes compatible with hyperkalemia and/or cardiac arrest. Rapid identification and treatment for hyperkalemia, with or without dexmedetomidine reversal, resulted in survival of 12 dogs and one fatality.Conclusions and clinical relevanceUnknown origin hyperkalemia is a life-threatening complication that can occur during general anesthesia. In healthy dogs, preanesthetic administration of dexmedetomidine in association with an opioid and followed by inhalation anesthesia of more than 1 hour duration may predispose to this complication. A sudden decrease in heart rate >90 minutes after dexmedetomidine administration, or ECG changes, may warrant measurement of blood potassium concentrations.     

Hyponatremia and hyperkalemia associated with idiopathic or experimentally induced chylothorax in four dogs

Two dogs with idiopathic chylothorax and 2 dogs with experimentally induced (ie, ligation of the cranial vena cava) chylothorax were treated by intermittent thoracic drainage. Of these 4 dogs, 3 that did not have evidence of renal failure had normal or near-normal serum sodium and potassium concentrations before thoracic drainage began, and all 3 developed repeatedly marked hyponatremia and hyperkalemia during thoracic drainage. Another dog became weak and depressed, ostensibly because of hyperkalemia. Serum sodium and potassium concentrations in 1 dog with spontaneous chylothorax returned to normal after chylothorax resolved and thoracic drainage was stopped. The other 3 dogs died or were euthanatized, and the effect of stopping thoracic drainage could not be evaluated. In 3 dogs in which it was measured, normal-to-high plasma cortisol concentration was observed before and after adrenocorticotropin administration, and 2 dogs also had hyperaldosteronemia. Hyponatremia was hypothesized to be caused by sodium loss via thoracic drainage whereas hyperkalemia may have been multifactorial in origin, but probably was attributable, at least, in part to decreased renal potassium clearance.     

Effect of an anti-inflammatory dose of prednisone on thyroid hormone monitoring in hypothyroid dogs

It is not uncommon for a hypothyroid dog to be receiving concurrent corticosteroids. As hypothyroid dogs receiving thyroid supplement need periodic monitoring, knowledge of whether prednisone alters thyroid hormone concentrations would be useful to determine whether testing can or should be done while the dog is receiving therapy and whether dose adjustments are appropriate. In this study, the effect of short-term anti-inflammatory prednisone was determined in dogs with naturally occurring hypothyroidism. Eight adult dogs were given prednisone (1.0 mg/kg, orally) daily for 7 days and then on alternate days for 14 days. Serum total thyroxine (T(4) ), free T(4) (fT(4) ), and thyroid-stimulating hormone (TSH) were measured on days 7, 21 and 28 and compared with baseline data. Total T(4) concentrations were significantly decreased after 7 days of anti-inflammatory prednisone, but were not significantly altered from baseline on days 21 or 28. Free T(4) and TSH concentrations were not significantly altered from baseline at any point during the study. Two dogs had decreased total T(4) concentrations on day 7, which may have resulted in an alteration in thyroid supplementation. Results showed that administration of prednisone at a dosage of 1 mg/kg, orally, once daily for 7 days decreased total T(4) , while fT(4) was unchanged, suggesting that fT(4) may be less affected by daily prednisone administration. Anti-inflammatory doses of prednisone administered every other day did not interfere with thyroid hormone monitoring.     

Thyroid-stimulating hormone and total thyroxine concentrations in euthyroid, sick euthyroid and hypothyroid dogs

Canine thyroid-stimulating hormone (cTSH) was measured in a variety of clinical cases (n= 72). The cases were classified as euthyroid, sick euthyroid, hypothyroid or hypothyroid on non-thyroidal therapy on the basis of their history, clinical signs, laboratory results (including total thyroxine concentrations and, where indicated, thyroid-releasing hormone [TRH] stimulation tests) and response to appropriate therapy. Additional samples were taken during some of the TRH stimulation tests to measure the response of cTSH concentrations following TRH administration. A reference range (0 to 0–41 ng/ml) was calculated from the basal concentrations of cTSH in a group of 41 euthyroid dogs. Six of nine cases of confirmed hypothyroidism had basal cTSH concentrations above the reference range, whereas the remainder were within the normal range. One of these three remaining cases was a pituitary dwarf and did not show a rise in cTSH concentration following TRH stimulation. In contrast, only one of a group of six hypothyroid dogs that had been on non-thyroidal treatment within the previous four weeks had increased concentrations of basal cTSH. This study also found that five of a group of 16 dogs with sick euthyroid syndrome had increased cTSH concentrations. It was concluded that cTSH measurements are a useful additional diagnostic test in cases of suspected hypothyroidism in dogs but that dynamic testing is still required to confirm the diagnosis of hypothyroidism.     

Proliferative responses to canine thyroglobulin of peripheral blood mononuclear cells from hypothyroid dogs

The immune responses of hypothyroid dogs to canine thyroglobulin (cTg) were evaluated for the proliferative ability of peripheral blood mononuclear cells (PBMC). PBMC from three hypothyroid dogs with high titers of thyroglobulin autoantibody (TgAA) and 3 clinically normal dogs were cultured with 5, 10, or 20 microg/ml of cTg for 72 hr. The proliferative responses of the cells were determined by the level of incorporated BrdU. The numbers of cells expressing Thy-1, CD4, CD8 and IgG in the PBMC were counted by the immunofluorescence method. Proliferative responses to cTg were observed in the cells from hypothyroid dogs. The number of cells expressing IgG and CD8 in the hypothyroid dogs tended to be high compared with the clinically normal dogs. The CD4+ cells in cultures from hypothyroid dogs increased depending upon the amount of cTg. There was a significant (P<0.05) positive correlation between the number of CD4+ cells and the concentration of cTg in the cultures from hypothyroid dogs. These findings suggest a possible relationship between canine hypothyroidism and cellular immunity. Loss of self tolerance to thyroid antigens in CD4+ T cells may play an important role in the development of canine hypothyroidism.     

Serum-free thyroxine concentrations, measured by chemiluminescence assay before and after thyrotropin administration in healthy dogs, hypothyroid dogs, and euthyroid dogs with dermathopathies.

The purpose of this study was to determine the usefulness of free thyroxine (FT4) measured by chemiluminescence in evaluating thyroid function in dogs. Total thyroxine (TT4) concentration measured by radioimmunoassay (RIA) and FT4 measured by chemiluminescence were evaluated in 30 healthy dogs, 60 euthyroid dogs with concurrent dermatopathies, and 30 hypothyroid dogs before and after intravenous stimulation with 1 or 2 IU of thyrotropin (TSH). Median basal TT4 and median TT4 concentrations at 4 h post-TSH administration were not significantly different (P < 0.0001) between healthy dogs and euthyroid dogs with dermatopathies, but were significantly higher than those in hypothyroid dogs. In healthy dogs, the median TT4 concentrations at 4 and 6 h post-TSH administration were not significantly different. Median basal FT4 and median FT4 concentrations at 4 h post-TSH administration in healthy dogs were significantly lower (P < 0.0001) than those in euthyroid dogs with dermatopathies, but significantly higher than the same parameters in hypothyroid dogs. There was a significant difference between the median FT4 concentrations at 4 h post-TSH administration and median basal FT4 concentrations for healthy dogs and euthyroid dogs with dermatopathies, but not for hypothyroid dogs. Lastly, in healthy dogs, median FT4 concentrations at 4 and 6 h post-TSH administration were not significantly different. Free thyroxine measured by chemiluminescence was highly correlated (P < 0.0001; Spearman r = 0.91) with FT4 measured by the reference method for free hormone analysis, namely, equilibrium dialysis, when sera from 56 dogs were used.     

Recognition pattern of thyroglobulin autoantibody from hypothyroid dogs to tryptic peptides of canine thyroglobulin

Circulating thyroglobulin autoantibody (TgAA) was analyzed using the Western immunoblot for determination of the dominant epitopes recognized by TgAA on tryptic peptides of canine thyroglobulin (cTg) in hypothyroid dogs. TgAA was measured in hypothyroid dogs, non-hypothyroid dogs with skin diseases and clinically normal dogs. Five of the 7 hypothyroid dogs, 1 of the 8 dogs with skin diseases and 1 of the 4 normal dogs were positive for TgAA. Four of the 5 TgAA-positive hypothyroid dogs were Golden Retrievers, and 3 of them showed high antibody titers. The sera of TgAA positive-dogs reacted to several peptides, and their patterns varied from sample to sample. Sera from 3 dogs with high titers of TgAA reacted broadly to high molecular weight peptides ranging from 45 to 90 kDa. These Western immunoblot patterns of the sera were disappeared after pretreatment with sufficient amount of intact cTg. All serum samples of both TgAA positive dogs and negative controls reacted to low molecular weight peptides ranging from 15 to 20 kDa. These immunoblot patterns of the sera were not disappeared even after pretreatment with sufficient amount of intact cTg. These findings show the possibility that the epitopes recognized by TgAA depend upon individual dogs with hypothyroidism and these autoantibodies recognize conformational epitopes on the cTg molecule.     

Thyroid sonography as an effective tool to discriminate between euthyroid sick and hypothyroid dogs

The diagnosis of canine hypothyroidism and its differentiation from euthyroid sick syndrome still is a major diagnostic challenge. In this study, ultrasonography was shown to be an effective tool for the investigation of thyroid gland diseases. Healthy control dogs (n = 87), dogs with euthyroid sick syndrome (n = 26), thyroglobulin autoantibody-positive (TgAA-positive, n = 30) hypothyroid dogs, and TgAA-negative (n = 23) hypothyroid dogs were examined by thyroid ultrasonography. Maximal cross sectional area (MCSA), thyroid volume, and echogenicity were measured. Statistical analysis identified highly significant (P < .001) differences between euthyroid and hypothyroid dogs both in thyroid volume and in MCSA, whereas no significant differences in thyroid size were detected between healthy euthyroid dogs and dogs with euthyroid sick syndrome. In euthyroid and euthyroid sick dogs, parenchymal echotexture was homogeneous and hyperechoic, whereas relative thyroid echogenicity of both TgAA-positive and TgAA-negative hypothyroid dogs was significantly lower (P < .001). When using arbitrarily chosen cutoff values for relative thyroid volume, MCSA, and echogenicity, thyroid volume especially was found to have highly specific predictive value for canine hypothyroidism. In summary, the data reveal that thyroid sonography is an effective ancillary diagnostic tool to differentiate between canine hypothyroidism and euthyroid sick syndrome.     

Use of recombinant human thyroid-stimulating hormone for thyrotropin stimulation test in healthy, hypothyroid and euthyroid sick dogs

Recombinant human thyroid-stimulating hormone (rhTSH) was evaluated for the diagnosis of canine hypothyroidism, using TSH response tests. Phase I stimulation tests were performed in 6 healthy dogs weighing over 20 kg, using 50 and then 100 microg of freshly reconstituted rhTSH administered intravenously. In phase II, the same dogs were stimulated by using 100 microg of rhTSH frozen for 3 months at -20 degrees C. Phase III stimulation tests were performed by using 50 or 100 microg of freshly reconstituted or frozen rhTSH in healthy (n = 14), euthyroid sick (n = 11) and hypothyroid dogs (n = 9). A dose of 100 microg of rhTSH was judged more appropriate for dogs weighing more than 20 kg. Biological activity of rhTSH after freezing at -20 degrees C for up to 12 weeks was maintained. When stimulated, significant (P < 0.05) increases in total thyroxine concentration were observed only in healthy and euthyroid sick dogs. Results of this study show that the rhTSH stimulation test is able to differentiate euthyroidism from hypothyroidism in dogs.     

Exercise-induced pulmonary hemorrhage

This article addresses many aspects of exercise-induced pulmonary hemorrhage (EIPH). Reports of the prevalence, effect on performance, and the clinical signs and means of diagnosis of EIPH are included. Radiologic and scintigraphic findings in horses with EIPH are reported. Pathogenesis and treatment are discussed.     

Prevalence of thyroglobulin autoantibodies detected by enzyme-linked immunosorbent assay of canine serum in hypothyroid, obese and healthy dogs in Japan

Thyroglobulin autoantibodies (TgAA) were detected in sera of hypothyroid (n=19), obese (n=28) and clinically healthy dogs (n=52) using a commercially available immunoassay kit. TgAA-positive results occurred in 10 of 19 hypothyroid, 1 of 28 obese and 1 of 52 clinically healthy dogs. The clinically healthy TgAA-positive dog had additional evidence of hypothyroidism supported by low total T(4), low free T(4) and high canine TSH. Among the breeds, Golden Retriever had the highest frequency of hypothyroid (9/19) and TgAA-positive hypothyroid dogs (6/10). This study was the first survey about the prevalence of canine TgAA in Japan and could be a useful reference for clinicians.