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Heart Wrenching

Dilated cardiomyopathy strikes nearly every Molosser breed – and its causes are far from clear.
It’s whispered ringside, gossiped on message boards and reluctantly discussed at the veterinary office. It’s a scarlet blaze on pedigrees that even the most forthright breeders will shirk. Yet it’s a major health concern of nearly every breed of Molosser. It kills quickly, with most Molossers succumbing within months of diagnosis, and it is not easily diagnosed prior to the onset of disease. It’s a complex health problem with no easy solution.
 
It’s dilated cardiomyopathy, or “DCM.”
 
In this serious disease of the heart muscle, the enlarged heart is unable to correctly conduct the electrical signal responsible for appropriate heart rhythm, and the distended muscle is also unable to effectively push the blood through the heart chambers into the lungs and body. Although what happens to the heart looks the same in many breeds, the underlying cause, clinical signs, response to treatment and prognosis can all differ depending on breed – a huge problem for breeders, owners and veterinarians alike. 
 
A Molosser owner once called me, distraught: His Rottweiler had died suddenly overnight, and the man was convinced the neighbors were involved, as they had had a heated argument about the dog the week before. I assured him that the best way to get definitive evidence was to do a post-mortem, or necropsy. The veterinary pathologist tested the dog’s tissues for common toxic substances, but the ultimate diagnosis was acute death due to generalized cardiac-enlarged DCM.
 
Visual examination of the hearts of dogs with DCM may show predominant dilatation of the left cardiac chambers. Histopathology (the results of microscopic examination of the heart tissue) can also vary; the thought is that differences result from the different causes that lead to the same heart malfunction. One study showed that when examined through standard clinical evaluation and with an echocardiogram (often called “echo” for short), 93 percent of DCM could be diagnosed.
 
But many different things can cause this end result of a dilated heart. In dogs, causes for DCM can include genetic, nutritional, metabolic, toxic and infectious influences. This huge variety of potential causes makes appropriate prevention a nightmare.  
 
One Molosser breeder was faced with an ethical dilemma after learning his dog’s grandsire died of DCM. This breeder planned to breed his health-tested champion dog, but now was hesitant due to this new piece of health history. Within the Molossers, the Great Dane is the breed most heavily studied; a 2001 pedigree analysis suggested that DCM in the Great Dane is inherited in an X-linked recessive fashion. However within the other large to giant breeds, the mode of inheritance is different. In the Irish Wolfhound, Newfoundland and Portuguese Water Dog, autosomal (or non-sex-linked) modes of inheritance are suspected. In Dobermans and Boxers, two highly studied breeds, the pattern of inheritance is still not well documented. With people, only 20 to 35 percent of DCM cases are considered hereditary.
 
The Molosser breeder’s dilemma was a real one. Since the dog in question was not from a breed that had any published genetic studies, I had no good information or insight to pass along. Keeping accurate, complete pedigree records and doing post-mortems on any suspect dogs to definitively diagnose DCM can help bring more information to the table on the individual pattern of inheritance for each of the Molosser breeds. 
 
There have been a number of studies on the importance of the amino acids taurine and carnitine on heart health. Looking over past studies, I was surprised by the number of asymptomatic dogs with apparently low levels of taurine and the large number of food brands that did not supplement with the amino acids. Since these amino acids are involved in so many critical aspects in the body, it’s not a far stretch to think that minor deficiencies may cause disease even if the clinical signs are hidden. Dogs are thought to be able to produce their own taurine and carnitine, thus making supplementation unnecessary; however, a number of studies now contradict this train of thought. Some dogs appear unable to appropriately make the amino acids or unable to make it in sufficient volume. Both taurine and carnitine, among many other factors, are involved in appropriate heart function, and low levels of one or both amino acids can cause symptoms of DCM. In Cocker Spaniels diagnosed with DCM, taurine supplementation can often reverse the disease process. Molosser breeds are very poorly represented in studies concerning DCM and taurine deficiency. 
 
Aside from heart problems, many Molossers are plagued with other health issues, including hypothyroidism. Looking at the breeds that have more than 50 OFA Thyroid submissions, a number of Molosser breeds appear in the top 50 of affected breeds on the registry’s database. Hypothyroidism, diabetes mellitus and pheochromocytoma (a neuroendocrine tumor of the adrenal glands) are metabolic disorders that have been associated with DCM in the dog. This crossover effect illustrates the importance of looking at the whole dog when diagnosing and treating DCM.
 
The most common element that has been associated with DCM is doxorubicin (Adriamycin), a common chemotherapeutic. 
 
The infectious causes of DCM, although considered rare in dogs, are perhaps the most troubling because there is very little research concerning their true incidence, and they can often be overlooked in the dog. 
 
Among viral causes, parvovirus is the best studied, but even then only a few cases have been identified where very young dogs (2 to 4 weeks of age) have developed signs of cardiomyopathy that can be directly linked to the viral infection. 
 
Another prevalent infectious disease that has been linked to DCM is borreliosis, a bacterial infection that causes Lyme disease. Lyme disease is transmitted by at least one species of tick, the Ixodes tick, which is found in many areas of the US. The disease is considered emerging by the Centers for Disease Control; they provide a map on their website illustrating the four categories of risk. Emerging or not, many veterinarians do not routinely test for the disease, so hidden, or occult, cases can go undiagnosed. Although Lyme disease can be controlled with common antibiotics and an infection seldom shows clinical signs of heart disease, little is known about the exact connection between the bacterial disease and DCM. Some studies in people have found the bacteria in heart cells of patients with new, unexplained dilated cardiomyopathy, while other studies have failed to find this connection. The major concern is that that signs of heart disease could emerge long after the initial infection of Lyme disease.
 
Infection with the tropanosome protozoa is even less common. Your veterinarian may not even remember the specifics concerning the two infectious diseases that it causes: Chagas disease, typically found in South America, and Leishmaniasis, found in many foreign countries. Many Molosser breeds are native to or are imported from breeders in these areas, which include the Mediterranean basin of Europe and Africa, the Middle East, and parts of South America, Asia and Africa. A number of studies indicate that the diseases are present in dog populations in the U.S., in dogs that may not even show signs. Although Chagas and Leishmaniasis are typically transferred by an insect vector – the reduviid bug and the sand fly, respectively – the two diseases have been shown to be transferred via blood and even during breeding, a scary thought for breeders. Specific work is being done by Dr. Peterson at Iowa State University to identify the prevalence of Leishmaniasis in the Neapolitan Mastiff population in the United States. 
 
It can be very difficult to directly link an infection to DCM. Many of the diseases can be hidden, and never be diagnosed or treated, instead simply resolving on their own or staying at such low levels so as never to be found. In some cases, the disease itself can be identified in the heart of a dog that has died from DCM, but there is also a chance that the causal disease – i.e., the tropanosome or bacteria – is no longer identifiable in the heart tissue when the dog dies from DCM. 
 
While considering all of the non-hereditary causes of DCM, it is important to remember that the condition has been shown to be hereditary in a number of breeds. Smart breeding practices such as pedigree analysis and testing with disclosure of affected animals can help minimize the genetic components of DCM. Health screening and regular health exams can help minimize the other causes of DCM. Only with appropriate education and surveillance can we help reduce this disease.
 
 

DCM at a Glance

 
Clinical Signs
Symptoms can vary, depending on how much the disease has progressed and the individual dog. Loss of appetite, lack of energy and fluid accumulation in the lungs and abdomen are common.
 
Diagnosis
Diagnosis is complicated, as the disease can be found before signs are noticed. A thorough cardiac evaluation is usually enough to find the disease. Screening exams can include  a 24-hour ECG recording.
 
Treatment
Treatment is usually very individualized, depending on the specific signs (or lack thereof) that the dog is showing. A range of drugs is often used, including a relatively new one, pimobendan. 
 
Prognosis
The prognosis is poor with DCM, as the disease is progressive, irreversible and ultimately leads to the death of the dog. Medical management of the disease can prolong the quality of life once the dog is showing signs.

 

About the Author

Dr. White is a breeder-veterinarian who breeds and shows Neapolitan Mastiffs. She owns a mixed-animal house-call practice in Oregon. She enjoys working with breeders and performance-dog enthusiasts and is a founding member of the Mastino Health Foundation.

 

 

 

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