From the tiniest Chihuahua to the largest Great Dane, dogs of all shapes and sizes come with the same basic body features: skin, bones, and muscles. But if you’ve noticed your dog looking thinner than normal, without any changes in their eating or exercise habits, or if you’ve found your older dog is having trouble getting around, you might be concerned. Is your dog losing muscle? What is muscle wasting in dogs? What causes it? When should you be worried?
What Are Muscles?
Muscles are the fleshy attachments to joints and bones that allow the body to move. They’re made up of various muscle fibers that work in conjunction or opposition to each other to move the joint. Muscles can be conditioned over time to increase in size and strength, and can also lose conditioning when unused or injured. They’re innervated by nerves running from the brain to the spine and outward. These nerves help control both the tone of the muscle, as well as when it should contract or relax.
What Is Muscle Wasting in Dogs?
Muscle wasting is the term for a muscle losing tone, shape, or size over time. You may also hear it referred to as sarcopenia, which is the general loss of skeletal muscle mass and function. Muscle wasting can occur for a number of reasons, from lack of use, to underlying illness, to aging-related problems. Depending on the cause, treatment and outcome can vary.
Dog Losing Muscle – General Signs to Watch Out For
Some general signs of muscle wasting to watch out for include loss of tone or size and shape of your dog. You may notice this change even if your dog hasn’t changed their eating or exercise habits. Other general signs of muscle wasting include weakness in the joints or limbs. Reluctance to stand or perform daily habits can also be a sign of something wrong. In addition to muscle wasting, your dog may have disease-specific symptoms as well.
If you notice sudden changes to your dog’s body, it is always best to talk with your vet. They can help determine if any of the following issues are to blame, and get your dog started on a treatment plan.
Dog Losing Muscle, Muscle Wasting — Causes
There are many causes behind muscle wasting, however, these are some of the most commonly seen:
Aging-related Loss of Muscle Tone
As your dog ages, they may naturally begin to lose muscle tone over time. This can be due to a number of aging-related factors, such as degenerative joint disease limiting activity. Changes in your dog’s eating or exercise habits and general slowing down may also occur. If your dog has gained weight due to age, they may also have changes to their muscles.
While this can be a normal part of aging, there is still much that can be done to keep your senior dog in shape and slow muscle loss. Keeping up with a regular exercise routine can help keep the muscles toned and in shape. Treating underlying illnesses and keeping the joints healthy with supplements like green-lipped mussel or methylsulfonylmethane (MSM) can also help. Many senior dog food diets have joint supplements such as glucosamine and chondroitin added to them. They are also sometimes lower in calories to help reduce age-related weight gain. By keeping your dog active, you also keep the muscles toned and reduce loss.
One of the most common causes of illness-related muscle loss is called cachexia, or chronic muscle wasting. It can be seen with many different illnesses, however, is a common symptom of advanced diseases such as cancer. Usually occurring in the late stages of illness, cachexia leads to full-body muscle wasting, loss of tone, and additional body changes such as loss of body mass and fat. Cancers of the digestive tract, such as pancreatic or stomach cancer, are the most likely to see severe cachexia. It is diagnosed generally through visual appearance, such as the loss of fullness in the face or body.
Since cachexia is a symptom, and not a direct illness, it isn’t really something that can be treated on its own. Instead, controlling the underlying cancer through chemotherapy, tumor removal, and palliative care can help reduce muscle and fat loss. In some cases, medications such as corticosteroids like prednisone may be given to increase appetite. That said, they’ve shown little promise in helping improve overall symptoms due to cachexia being secondary in nature.
Myositis (Muscle Inflammation)
Inflammation may make you think of swelling increasing size rather than decreasing it. However, myositis, or inflammation of the muscles, can also lead to muscle wasting in dogs if prolonged. It is often an indication of other problems ongoing in the body. Often, it causes painful swelling of the muscles. It can affect just a single muscle or the whole system. Myositis can also affect any muscle in the body, from the eyes to the legs.
Affected dogs may have trouble moving the inflamed muscles, or may have a sudden change in gait or activity levels. If muscles surrounding the digestive tract are affected, you may also see vomiting, diarrhea, or changes in appetite. Myositis can be caused by many underlying conditions. These include infections or parasites affecting the muscles, immune system conditions, and some cancers. Examination, bloodwork, X-rays, and more can be done to narrow down the underlying cause and find the right treatment option.
Treatment depends on the underlying cause of the inflammation. Antibiotics and antiparasitics can help treat parasites or bacteria present. Steroids can help reduce the body’s inflammatory response. Pain medications and physical therapy may also be helpful for reconditioning muscles and reducing pain.
Just like the rest of the body, muscles need nutrients in order to stay healthy, replenish lost tissue, and keep in shape. Muscles are made up of protein strands, however, there are many nutrients they require. In addition, lack of nutrition in the whole body also affects the muscles. If a body is without the right nutrients for long enough, it will first break down any fat stores in the body. From there, the body will break down muscle proteins in an attempt to keep important body systems alive.
Macronutrients such as proteins, carbohydrates, and fats are often the most common deficiency in muscle loss. However, if there is an underlying illness that affects other body systems, such as kidney disease, imbalances of micronutrients such as phosphorus or potassium can also lead to muscle wasting. Diagnosis involves full blood work to check for nutritional deficiency and underlying illness such as kidney disease or food allergies. A complete history, including your dog’s activity levels and health history, is also beneficial.
Treatment varies depending on the cause. Addressing any underlying illnesses that can cause nutritional imbalance is best. Any ingredient allergies should be replaced with tolerated foods to allow for maximum absorption of nutrients. If there has been a change in your dog’s activity levels, such as switching to higher intensity exercise, supplementing additional nutrients can reduce the chances of deficiency. A well-balanced diet or a diet formulated to your dog’s needs such as large breed or high protein foods can help.
In the case of pregnancy and lactation, additional fats and carbohydrates are best. This will prevent the body from breaking its own tissues down to provide nutrition for puppies in these life stages.
Chronic Diseases (Heart Failure, Kidney Disease)
As with nutritional deficiencies, chronic disease can lead to muscle wasting. This can occur both due to a loss of nutrients in chronic illness or as a side effect of the illness itself. Often, imbalances of micronutrients such as phosphorus or potassium or prolonged stress on the body can be a cause. Symptoms depend on the underlying illness. Exercise intolerance, trouble breathing, and swelling of the chest can indicate heart failure. Excessive urination and thirst, vomiting and diarrhea, and changes in appetite can be a sign of kidney problems.
Most chronic diseases are diagnosed by a thorough workup from your vet. Bloodwork is standard to check for organ dysfunction. X-rays can be used to check the lungs and chest for fluid, as well as the size of the heart and kidneys. More specialized tests, such as tissue biopsies or EKGs of the heart can further determine what is going on.
In many cases, treatment is palliative, focusing on reducing symptoms. Diuretics to remove excess fluid from around the chest may ease heart congestion, along with supplemental oxygen. Longer term, medications to regulate blood pressure can help. Medications to support the kidneys can help slow the loss of function. IV fluids, as well as specialized diets, may also be needed to supplement lost nutrition. Like in human medicine, kidney transplantation is possible, however, it is relatively rarely done in pets. Kidney removal, such as with cancers, may also help improve overall health.
Prevention in these cases is often difficult. These problems may be genetic, come on suddenly, or progress rapidly before symptoms appear.
Many specific breeds are prone to genetically related diseases that can lead to muscle wasting. Some cause degeneration of the nerves that innervate the muscles, such as with Dancing Doberman Disease. Others can affect the muscles themselves, as with Labrador Retriever Myopathy. Great Dane Myopathy is another breed-related condition.
Depending on what the underlying disease process affects, such as the nerves or muscles, symptoms and treatment can vary. In most cases, nerve-related conditions will present with difficulty walking, stiffened gaits, loss of proprioception (ability to know where a limb is in relation to the body), and eventually muscle wasting. For dogs with muscle-related conditions, the muscles may be affected first. Dogs with muscular myopathies may have loss of muscle mass or may not have normal muscle growth. They, however, will still have normal movement and gait. Most affected breeds will show signs early in life that slowly progress over time.
Nerve-related breed myopathies gradually worsen over time and have limited treatment options outside of keeping the dog as healthy and comfortable as possible. In muscle-related myopathies, such as Labrador Retriever Myopathy, the dog may have a progression of symptoms until adulthood and then stabilize. There may also be long-term symptoms such as shaking or trembling of the muscles. Testing involves urine testing as muscle wasting usually produces byproducts found in the urine. Supplementing with amino acids such as L-carnitine may help slow progress.
Fibrotic Myopathy is an uncommon illness. It involves wasting of the muscles of the upper leg and thigh only. No other muscles are affected. Symptoms include loss of mass of the thigh and hip muscles, along with a stiffening of these muscles. This can lead to an abnormal gait or limp.
Diagnosis involves ruling out other issues such as injuries or nerve damage to the hind legs. Tissue samples to check for changes in the muscle makeup, such as changes in the connective tissue thickness, can also help diagnose this condition. Treatment is limited, however, surgery and physical therapy may help loosen tight muscles and allow for more normal movement. Prognosis is also guarded, as dogs can have a relapse of symptoms after the initial incident has cleared up. Since the cause of this disease isn’t known, there aren’t any preventive measures that can be taken.
Polymyositis refers to the inflammation of the muscle tissues. It can occur in both a chronic and acute form, with symptoms coming on suddenly in the acute form. Affected dogs may be reluctant to move, lethargic, or lose weight. Rapid muscle mass loss can also occur. Affected muscles may also become swollen or painful.
Diagnosis is done through several tests. Bloodwork can rule out inflammatory conditions and immune-mediated polymyositis. Electromyography (measuring the electrical conduction through muscles) and muscle biopsies can rule out other causes. Corticosteroids such as prednisone can work in acute cases to relieve swelling and inflammation. Prognosis is usually good, even in acute cases that become long-term. Additional physical therapy and rehabilitation can help dogs that have had severe muscle wasting.
Like Acute Polymyositis, Immune-mediated Polymyositis presents with similar symptoms. These include lethargy, pain and swelling of affected muscles, and muscle wasting. Since the condition is also immune-related, other symptoms occur that differentiate it from acute non-immune cases. This includes full-body systemic symptoms such as fever, vomiting, diarrhea, and general malaise. Immune-mediated polymyositis is often a secondary result of other immune system conditions, such as Lupus.
Diagnosis and treatment of Immune-mediated Polymyositis is similar to its acute form. Bloodwork and biopsy of the muscle can be used to rule out other conditions. Unfortunately, diseases such as Lupus are often diagnosed by ruling out other diseases, rather than specifically testing for it. This can lead to delays in treatment and diagnosis. However, treatment with corticosteroids such as prednisone is effective in treating polymyositis until a longer-term treatment plan can be created.
Prevention is easier if the underlying condition is kept under control through long-term medication treatments. If the underlying condition is treated, it can reduce the chances of polymyositis recurring.
Masticatory Myositis, or inflammation of the jaw muscles, gets its own mention due to the uniqueness of the condition. It is unknown why this condition happens specifically, but it is thought that the immune system may be to blame. If the immune response affects the muscles of the jaw specifically, it can lead to difficulty chewing. Other signs of Masticatory Myositis include swelling of the face and jaw, pain, loss of appetite (due to inability to eat), and loss of muscle mass in the face.
Like other types of myositis and polymyositis, diagnosis is through blood work and testing of the muscle fibers to rule out other issues. As with other muscle inflammation, treatment with corticosteroids like prednisone usually produces good results. However, Masticatory Myositis may also go away spontaneously. In some cases, the acute condition may progress to long-term disease. Continued treatment with medications can help reduce symptoms and allow normal movement of the jaw.
A condition common in sporting dogs, especially racing breeds like Greyhounds, Exercise-Related Rhabdomyolysis can cause rapid muscle wasting. Symptoms are sudden and appear 24-72 hours post exercise. It is most often triggered after an intense exercise event, such as a sporting event, race, or work out in the field.
The intense exercise leads to the rapid breakdown of muscle tissue, which then overloads the kidneys. In turn, the kidneys are not able to quickly remove these byproducts of muscle breakdown, leading to acute kidney failure. Along with signs of kidney disease, such as changes to thirst and urination, an affected dog may have swelling or severe pain in the affected muscle.
Urine tests are used to diagnose this condition In addition to blood work. Byproducts of muscle breakdown are filtered by the kidneys and released into the urine in high quantities. IV fluids to support the kidneys, supportive care, and electrolytes can help. Cooling the body, and resting the muscles may also help slow or stop progress. Avoiding intense exercise sessions, and gradually building up stamina may help prevent an event from occurring.
Injury to the muscle, without an underlying medical condition, can also lead to muscle wasting in dogs. This can appear in many different ways, depending on the injury sustained. Dogs with injured muscles may be reluctant to stand on or use the affected limb, and may limp as a result. The limb may also abnormally contract on one side, or lose overall tone and mass. Pain and swelling at the affected area may also signify an injury. Muscle injuries can be acute, with symptoms occurring rapidly, or may come on more gradually over a period of weeks to days.
Diagnosis involves ruling out any underlying health issues, such as immune system conditions or nutritional problems. This is done via bloodwork, X-ray, and sometimes muscle biopsy. A complete history is also beneficial to note any events such as a trip or fall that could indicate an injury occurred. Depending on the cause of the injury, and its location and severity, treatment will vary. Conservative options include pain medications, anti-inflammatories, and kennel rest. This can help the muscle to repair itself in minor injuries.
Physical therapy and surgery may also be options in cases where the muscle can’t repair itself. Surgery can help to relieve tension on abnormally tightened muscles, or remove them completely. Physical therapy, such as underwater treadmill therapy, can help rebuild lost muscle mass and range of movement. Prevention involves reducing the chances of an injury through safer exercise, and gradual build up of intensive routines to build up muscle strength.
Like muscle injuries, nerve injuries can also cause muscle loss in dogs. While the outward appearance may be similar, including lameness, pain and swelling, and loss of mass, the underlying reason is different. Nerves innervate the muscles and give them the signal to move. When there is damage to the nerve, it can’t properly send a signal to the muscle it is connected to.
Since a different set of nerves innervate each side of the limb (alternating which side contracts, and which relaxes), the muscle may appear twisted or constricted to one side. If the entire limb is affected, the entire limb may be locked in place, or hang loosely. If a nerve in the neck or spine is affected, all of the muscles behind it, including the ones controlling muscle tone of the bowels and bladder, may lose normal function.
Diagnosis involves ruling out other conditions, as well as a history to determine if any injury occurred. Treatment greatly depends on the severity of the nerve injury and its location. While nerves can heal, healing is slow, and if not resolved within a year, usually does not heal at all. Surgical repair or amputation of limbs or affected nerves may help. Conservative treatment such as kennel rest and pain and anti-inflammatory medications may help with minor injuries. In the case of full-body paralysis, humane euthanasia may be recommended.
Muscle wasting in dogs can be a serious concern. Keeping your dog healthy and in good physical condition can help with minor issues, but extreme changes should always be checked out by your vet. With proper care and treatment, you can help your dog stay active and in shape longer.