Hypothyroidism and DCM in Doberman Pinschers | VETgirl Veterinary CE Podcasts

In today’s VETgirl online veterinary continuing education podcast, we review whether or not there is an association between hypothyroidism and dilated cardiomyopathy (DCM). Doberman Pinschers are overrepresented among canine patients diagnosed with dilated cardiomyopathy (familial/genetic), as well as those diagnosed with hypothyroidism. So the question is, is there a link? This is a very controversial topic. After all, we know that thyroid hormone plays an important role in the systolic function of the myocardium and cardiac rate and rhythm via its effect on density of beta-adrenergic receptors and their sensitivity to catecholamines. A deficiency of thyroid hormone has been associated with reduced myocardial function and alterations in cardiac conduction and heart rate thus leading to the premise that the hypothyroid state may be a metabolic etiology for dilated cardiomyopathy. Studies to date have not supported that premise.

So Beier et al, out of the University of Munich in Germany, performed a prospective clinical trial to evaluate if there was any link in a study called “The Role of Hypothyroidism in the Etiology and Progression of Dilated Cardiomyopathy in Doberman Pinschers.” They evaluated 175 Doberman Pinschers with two phases of the study; the first phase was purely looking at concurrent diagnosis of DCM and hypothyroidism, while the second phase evaluated follow-up (specifically looking at those dogs with concurrent DCM and hypothyroidism undergoing treatment of hypothyroidism).

Dogs with any other systemic illness or those receiving drugs that might influence the thyroid gland (such as corticosteroids or phenobarbital) were excluded from the study. Of the 175 dogs, 107 were healthy (61%), while 45 dogs were diagnosed with DCM (26%). 11 dogs (6%) had hypothyroidism, while 12 dogs (approximately 7%) had both hypothyroidism and DCM. DCM status was determined via echocardiogram and Holter monitor analysis. All dogs diagnosed with DCM were placed on pimobendan. Those dogs that had either congestive heart failure (CHF) or significant ventricular arrhythmias were also placed on treatment for CHF or antiarrhythmic therapy, respectively, if warranted.

The diagnosis of hypothyroidism was determined via combination of thyroid ultrasonography and serologic testing including one or more of the following: TT4, TSH-stimulating test, fT4, cTSH, TgAA, T4AA. In dogs confirmed to be hypothyroid, treatment with 0.02 mg/kg of levothyroxine orally every 12 hours was initiated, with doses titrated accordingly based on follow-up values and monitoring. (FYI, for those dogs that were actively in congestive heart failure, levothyroxine was initiated at 0.01 mg/kg instead).

As thyroid levels can be altered with illness, it’s important to rule out euthyroid sick syndrome. In this study, the authors stated that euthyroid sick syndrome was relatively uncommon in this population of Doberman pinschers (7 total dogs). Beier et al defined euthyroid sick syndrome as the combination of the following three parameters: a low total T4 while all other thyroid testing parameters were normal, and the identification of DCM (thus DCM deemed to be the concurrent nonthyroidal illness).

Overall, this study found that the prevalence of hypothyroidism was higher in the DCM group (12/57, 21.1%) compared with the healthy group (11/118, 9.3%). Doberman pinschers with hypothyroidism had a 1.76 greater risk of developing DCM, while Doberman pinschers with DCM had a 2.28 greater risk of developing hypothyroidism.

In dogs that were diagnosed with only hypothyroidism (in other words, this group did not have concurrent DCM), there was no measurable difference in cardiac size or arrhythmia frequency noted compared with healthy dogs. In dogs that were diagnosed with only DCM (in other words, this group did not have concurrent hypothyroidism), no measurable effect on TT4 levels was noted compared with healthy dogs. As for those dogs that had both concurrent DCM and hypothyroidism, parameters of cardiac size and function continued to decline despite confirmed optimization of thyroid levels throughout treatment.

So what did this study find? A link/relationship between DCM and hypothyroidism in Doberman pinschers was demonstrated; however, this did NOT appear to be a causal relationship. Continued decline in cardiac function and arrhythmia severity occurred despite correction of thyroid levels (with treatment) in Doberman pinschers with both DCM and hypothyroidism in this study. Note, there have been a small number of case reports/series in the literature whereby dogs were diagnosed with both DCM and hypothyroidism concurrently, and their myocardial dysfunction was later documented to resolve with correction of their hypothyroidism. The most recent was a case report in two Great Danes. Unfortunately, as this article seems to further prove, these case reports are the exceptions, not the norm. Therefore, Beier et al suggest that the link between the two conditions may be a function of the genetics of Doberman pinschers (independently predisposed to both conditions) or a function of age (as both diseases tend to occur in older dogs). A common etiology (e.g., immune-mediated) was also considered.

So, what can we take from this VETgirl podcast? Doberman pinschers with DCM are at increased risk of developing hypothyroidism, and vice versa, but the relationship does not appear to be causal based on the results of this study. The relationship may therefore be due to shared genetic risk factors, age as a shared risk factor, or a common etiology as of yet not identified. While it’s important to treat hypothyroidism, it’s not a direct cause for DCM in the Doberman Pinscher.

CHF: congestive heart failure
DCM: dilated cardiomyopathy
cTSH: canine thyroid stimulating hormone
fT4: free total thyroxineTT4: total thyroxine
TgAA: thyroglobulin autoantibodies
T4AA: autoantibodies against TT4
TSH: thyroid stimulating hormone

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