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Veterinary Forum April 2008 (Vol 25, No 4)

Canine Geriatrics — head to tail

by C. J. Ellis

    Getting old is not a disease, but it does complicate how senior dogs are treated — especially now with the growing number of aging pets

    Old age is not a disease, the experts remind everyone, but it can involve a multitude of problems — some that may be predictable, and some that are not.

    Veterinary medicine, unlike its human counterpart, is still in its infancy when it comes to specialization, says Sonya Gordon, BSc, DVM, DVSc, DACVIM (Cardiology). Human medicine specialties have been around a long time, which might explain why gerontology is such a hot topic — or is it because the baby boom generation is entering the scene?

    Alongside the baby boom generation of owners is the growing number of aging pets. "The average age of dogs is older," Gordon says, "and with senior dogs, you have to treat the entire body because all systems are interrelated. It does, however, make treating each disease more difficult."

    Click to see box Senior Dogs and the Role of Nutrition

    Window to the body

    Paul E. Miller, DVM, DACVO, a past president of the American College of Veterinary Ophthalmologists, agrees that treating an aging pet population means treating the whole body.

    "Most general practitioners are aware that the eye is the window to the interior of the body, and many diseases often are initially visible through an ophthalmic examination. Because of the transparency of the cornea and the lens, the eye is the only place in the body where you can directly see the arterial and venous systems by looking at the fundus," explains Miller, who is clinical associate professor of ophthalmology at the University of Wisconsin"Madison School of Veterinary Medicine.

    "Many conditions may first present as an ophthalmic problem, such as systemic hypertension, which can cause fluid to accumulate underneath the retina, vascular changes or bleeding into the back of the eye," he says.

    Likewise, diabetes may become apparent through the sudden onset of cataracts, and various coagulation disorders will show up as bleeding, he adds.

    In fact, a whole section of ophthalmology, called ocular manifestations of systemic disorders, represents what a large percentage of veterinary ophthalmologists see — disorders that are not exclusive to the eye but reflect other underlying health abnormalities.

    What are the primary problems affecting geriatric dogs? "They all will develop nuclear sclerosis, a compaction of the fibers of the lens that often gives an older dog a blue-looking lens," Miller offers. "In some cases, it is easy to mistake this condition for a cataract."

    But the two problems are distinguishable, he says, by using an ophthalmoscope to check the retina. "With nuclear sclerosis, you can see through [the sclerosis], whereas with a cataract, you won't be able to see through it."

    There also is a tendency for older dogs to develop age-associated, or senile, cataracts. The exact cause, however, remains unclear. "People with this type of cataract have it surgically repaired because it interferes with the vision they need for everyday activities, such as driving, but most senior dogs are not affected from a quality-of-life standpoint," Miller says, adding with a smile that dogs don't need to drive, read or do needlepoint.

    However, cataract surgery should be considered in an older dog if vision impairment is affecting its quality of life.

    If a senior dog is not a good candidate for cataract surgery because confounding systemic disease precludes anesthesia, Miller says that practitioners need to explain how owners can help the pet adjust to having poor or no vision. "I recommend that owners read the book Living with Blind Dogs because it is a useful aid in ensuring quality of life for vision-impaired dogs."

    One exciting treatment for diabetic cataracts that is currently undergoing testing shows promise, he adds. Peter Kador, PhD, professor, department of pharmaceutical sciences at the University of Nebraska Medical Center, teamed up with two veterinary ophthalmologists, Milton Wyman, DVM, DACVO, from The Ohio State University, and Daniel Betts, DVM, DACVO, from Iowa State University, in developing an eye drop that inhibits aldose reductase, an enzyme actively involved in the onset of diabetic cataracts in dogs.

    "Preliminary studies suggest that the drug will likely make a difference in preventing the formation of diabetic cataracts," Miller says. "About one-half of our patients [at the University of Wisconsin] undergoing cataract surgery are diabetic, and if we could prevent our diabetic patients from developing cataracts, I think we could make a significant improvement in their lives."

    In addition, other individuals are working on breakthrough treatments for retinal disorders in dogs, Miller says, including gene therapy in dogs with genetic retinal disorders. By inserting the desired gene underneath the retina, some improved vision has been demonstrated in these dogs.

    Gus Aguirre, VMD, PhD, DACVO, professor of medical genetics and ophthalmology at the University of Pennsylvania, and Kristina Narfstrom, DVM, PhD, DECVO, the Ruth M. Kraeuchi endowed professor of veterinary ophthalmology at the University of Missouri, have both received national media attention for their work in genetics and ophthalmology, Miller adds.

    Orthopedics — moving in the right direction

    In the case of orthopedics, revolutionary technology is already on the scene, says Darryl Millis, DVM, CCRP, DACVS, a professor of small animal clinical sciences at The University of Tennessee College of Veterinary Medicine.

    From total hip replacement to regenerative cellular therapy, to shock wave therapy, orthopedics today offers a bright future for tomorrow's generations of dogs.

    "Hip replacements are fairly common now at referral facilities," Millis says, "and senior dogs that are free of major underlying medical conditions can be good candidates for the procedure." He does, however, prefer to exhaust more conservative approaches first.

    "Although hip replacement is very successful, there are complications, including dislocation, infection or loosening of the implant, so I make sure we first try dietary and medical management with NSAIDs, Adequan, a prescription diet such as Hill's Prescription Diet Canine j/d or other joint disease diets, omega-3 fatty acids and rehabilitation."

    Millis advocates general strengthening and conditioning, active joint range of motion and aquatic exercises. "Aquatic exercises are extremely beneficial for arthritic patients because the buoyancy of water reduces force and concussion on painful joints, and the resistance of water helps with muscle strengthening and cardiovascular fitness. Underwater treadmill walking likewise is valuable for patients with moderate to severe osteoarthritis," adding that joint flexion and overall range of motion are increased with underwater walking.

    The bottom line, though, is that practitioners have to work hard in managing the disease process, Millis says. "Just because you start with one combination of treatments doesn't mean it will always be effective, so identifying what works best for the individual dog may require numerous trial therapies and constant reevaluation. The goal is to help patients become more comfortable for the duration of their lives."

    Toward that end, some new approaches are gaining respect quickly, including adipose-derived stem cell therapy. "I was certified to perform the procedure last year," Millis says, "and the dogs we treated had fairly severe arthritis. Most of them have responded well."

    The procedure, he adds, does not require an orthopedic specialist, and Kathy Mitchener, DVM, an oncologist and certified acupuncturist involved in the pain management of all patients, including those with osteoarthritis, agrees: "This procedure is perfect for osteoarthritis patients with some other problem that precludes aggressive treatment because stem cell therapy is so minimally invasive."

    How does the therapy work? "The honest truth is that no one knows exactly how stem cells turnaround the pathways," explains Mitchener, who owns Angel Care Cancer Clinic for Animals, in Memphis, Tenn.

    "We know that the processes of osteoarthritis are catabolic and destructive and that stem cells produce factors that halt this destructive process, turning it into an anabolic process that builds up rather than tears down. We know that the treatment stabilizes cartilage, produces factors that improve the integrity of the joint fluid and decreases inflammation, thereby improving pain and joint mobility."

    Both Millis and Mitchener add that the credentialing process is clear and easy to follow and involves taking a test after each module has been completed, although practitioners can review modules as often as necessary.

    "Once you pass the credentialing course," Mitchener says, "Vet-Stem overnights all essential harvesting supplies. The company is there 24/7 to answer your questions. Plus, specialists such as Jamie Gaynor [at Colorado Pet Rehabilitation] are very gracious about addressing your concerns."

    Mitchener did just that when she was apprehensive about harvesting cells from the shoulder of a very thin dog, and the recommendation was to harvest abdominal fat instead. "The reality is that, technically, harvesting from the abdomen is easier than doing a spay procedure," she says.

    Both Millis and Mitchener say that with critical, elderly patients, it is important the procedure be done quickly, and the last abdominal harvest and injection series Mitchener did required only 45 minutes for each procedure.

    After two tubes — about 50 grams — of fat are harvested, they are sent overnight, along with a blood sample, to the company, where the stem cells are processed and sent back to the practitioner — all within 48 hours.

    "When the patient returns, we use a lighter plane of anesthesia to inject up to three individual joint doses, along with one intravenous dose," explains Mitchener. Stem cell therapy provides the opportunity to treat the pain associated with osteoarthritis as well as decrease inflammatory response.

    Although relatively new in small animal medicine, another technology gaining ground is shock wave therapy.

    "We have done some preliminary work that shows this procedure is as effective as NSAID therapy in terms of increasing weight bearing," Millis says.

    "A high-energy acoustic wave — basically a sound wave — is transmitted through the tissue and reaches a designated depth, where it releases its energy, causing an increase in cell activity, growth factors and blood vessel infiltration for healing purposes, as well as probably some form of analgesia we really don't understand yet." It is the same technology used in lithotripsy, he adds.

    And the beat goes on

    Although it may not seem as exciting and glamorous as some of the breakthrough technology in orthopedic disease, Gordon says, degenerative valve disease remains the number one cause of heart failure in dogs. "Because it is so common, it is taking its toll more than any other defect or disorder."

    Treatment of valve degeneration differs according to the clinical stage of the disease. So, she adds, when it comes to treatment, there is sad news and there is happy news.

    "The happy news is that, although the disease is terminal, treatment of the clinical stage — once the dog starts coughing and having breathing problems — is now good with the licensing [in 2007] of pimobendan [Vetmedin, Boehringer Ingelheim Vetmedica]."

    In the final stage, Gordon explains, dogs can be really sick. "Because the heart is so tired, we strengthen it and off-load it to reduce the work load as well as inhibiting the mechanisms that lead to progression and, ultimately, death."

    So although in some respects it is a simple disease, it really is not that simple to treat because practitioners need to think of it in terms of stages — before dogs are sick and after dogs are sick, she stresses.

    "And that is the sad news," Gordon adds. "Although we have a good handle on helping these dogs after they are sick, it is a terminal disease, so it would be nice to prolong the asymptomatic stage. However, to date, no medication has been demonstrated to significantly slow this disease's progression in its early stages. But we are moving forward in this regard."

    For instance, some novel agents look intriguing based on scientific rationale and experimental model data, and researchers are actively investigating in this area, with the goal of identifying an oral agent that, when initiated early, will delay the onset of heart failure.

    "Some researchers are specifically pursuing identification of the underlying etiology of degenerative heart disease, including the elucidation of signaling pathways with potential genetic implications," Gordon says.

    "I realize it is not glamorous to give a dog medicine every day for 3 or 4 years, but if it can keep the dog alive longer with quality of life, I think that would be exciting," she adds.

    Heart diseases may not be glamorous, Gordon says, but they are real, so primary care practitioners need to look at the heart in that context when dealing with mature populations. "The heart is living in an aging body that is at risk for many comorbidities, such as kidney disease, systemic hypertension, endocrine disease, orthopedic disease, respiratory disease, etc.

    "If a dog has leaky valves, what effect does that have on other organs? In the long run, it leads to reduction in cardiac output, and eventually the dog may develop breathing problems because of edema in the lungs."

    And all this is happening to the same population that is affected by so many other diseases. "Heart disease in an aging dog means you likely are not going to be treating a 'normal' dog. For instance, the same signs that happen with respiratory disease happen with cardiac disease — they mimic each other. But treatment for one is not the right treatment for the other."

    On the horizon, however, are novel tests, such as measurement of levels of circulating biomarkers in the blood. These tests will undoubtedly help primary care practitioners diagnosis, stage and treat heart disease in both the dog and cat.

    "NT-pro BNP [N terminal pro B-type natriuretic peptide] is getting a lot of attention, and there will be new material published in JAVMA in the next few months and new data presented at the annual ACVIM Forum in June," Gordon says.

    "What is currently one of the most exciting aspects of veterinary cardiology," she explains, "is the plethora of recent and ongoing multicenter national and international clinical studies.

    "As a specialty, we are moving into the era of internationally recognized evidence-based medicine, and companies are taking these common diseases seriously by investing in developmental research and clinical trials designed to answer questions that have the potential to impact the lives of many dogs. Some of these studies are not glamorous, but they are necessary."

    The future is bright, she says, "because there will be answers to some of these questions before I retire."

    That's good news — for general practitioners, for pet owners and, of course, for the baby boom generation of senior dogs.

    NEXT: Clinical Report: Common disease is often overdiagnosed

    didyouknow

    Did you know... According to the American Animal Hospital Association (AAHA), only about 14% of senior animals undergo regular health screenings as recommended by their veterinarians.Read More

    These Care Guides are written to help your clients understand common conditions. They are formatted to print and give to your clients for their information.

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