Muscle Loss in Dogs and Cats

Author: Dr. Beth Turner

Published: December 20, 2023

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senior dog and cat sleeping together by the fire

With age comes beauty but also aches, pains, and muscle loss. And this isn’t just in people. Pets suffer the same issues as they age. But it's not only aging pets that can suffer from loss of muscle that can lead to aches and pains.

People are fortunate in that they can express how their body is feeling. Sadly, our beloved pets can’t. That is why it is important to understand how to assess your pet’s body condition as well as muscle condition. This combination gives a better overall picture of your pet’s health.

Recognizing that your pet is losing muscle mass is critical since it can indicate any number of underlying medical issues, some of which are very serious.

There are various medical conditions, such as heart disease, kidney disease, or cancer, that cause loss of muscle. This can be caused by the production of high levels of hormone-like substances that cause muscle loss, dysregulation of muscle protein metabolism, or impairment of muscle cell regeneration.

Other reasons pets may lose muscle are genetics, decreased activity due to injury, arthritis or weight gain, certain medications (e.g., corticosteroids ), or parasites. More causes of muscle loss are listed below.

When pets lose muscle mass, they can suffer with:

  • Weakness
  • Poor mobility
  • Pain
  • Poor immune function which decreases their ability to heal from illness, injury, or surgery.

There Are Two Kinds of Muscle Loss in Pets

What exactly does muscle loss mean? Simply put, it is when the muscles of your pet’s body waste away. Muscle loss falls under two general headings, and knowing the difference is helpful.

To complicate matters further, both can occur at the same time in older pets. This increases their risk of injury and disease and lowers their body’s immune system, hindering recovery.

Cachexia

When muscle loss is due to chronic disease (heart disease, kidney disease, cancer, etc.), it is referred to as cachexia. This is also the term used when muscle loss is due to injury or acute (sudden) illness. Cachexia can hinder recovery due to the negative effects it causes (i.e., it weakens the immune system).

Sarcopenia

When muscle loss is associated with aging, in the absence of disease or illness, it is referred to as sarcopenia. Just like us, as our pets age, their muscle mass diminishes, but their fat mass increases. That is why their weight seems stable. This is why muscle loss can often be missed in older pets.

Another issue with sarcopenia is that the remaining muscle doesn’t function as well. This is why older pets have increased physical disabilities, like getting up from their bed.

As mentioned, fat replaces the muscle. This makes some people think their pet has lost weight (fat), but they likely gained more fat and lost the weight in muscle mass.

Besides weight loss and weakness, you may also notice the following with muscle loss:

  • Muscles are flabby, soft, and weak
  • Muscles are visibly thinner
  • Sunken muscles
  • Poor coordination
  • Abnormal gait
  • Limping
  • Dragging paws
  • Weakness that is progressive in the hindlimbs
  • Changes in posture where the back may appear to be sagging
  • Difficulty getting up or standing

Several years ago, one of our team member's dogs was losing muscle mass in his hind legs as he aged. They used a wheelchair to help their senior pup walk – as he easily fell over without the assistance of a sling or wheelchair. This helped him use his muscles and lessen the speed of deterioration. Read more tips on helping your dog or cat with mobility issues.


 


How to Know If Your Pet Is Suffering from Muscle Loss

Knowing how to assess muscle condition is essential and should be done routinely throughout your pet’s life. The sooner you notice changes in your pet’s muscle condition, the quicker the cause can be diagnosed, and treatment or management of the condition can be started. The earlier treatment is begun, the more likely it will be successful.

When you delay having your pet’s weight or muscle loss evaluated by a veterinarian, it is possible that irreversible damage can occur to their body that shortens their lifespan.

How to Assess Your Pet's Muscle Condition

You will need to use visualization along with touch to determine your pet’s muscle condition. Your veterinarian does this assessment every time your pet goes for their wellness exam.

A 4-point muscle condition score (MCS) assesses your pet’s muscle mass over their spine, shoulder blades, skull, and hip, and then a grade of normal, mild loss, moderate loss, and severe loss is given to each location.

This chart shows the four levels of muscle loss and what to look for. The chart shows a dog, but the same applies to a cat.

NOTE: The epaxial muscles, those on either side of the spine, are typically where you will not see muscle loss first. Other locations can be variable.

Normal muscle mass: When there is almost no depression in the area when pressed with your finger, or you are unable to pinch up tissue between your thumb and fingers.

Mild muscle loss: If you can slightly depress tissue with your finger or pinch up a small amount of tissue between your thumb and fingers.

Moderate muscle loss: When you can clearly depress tissue with your finger or obviously grab tissue between your thumb and fingers.

Severe muscle loss: When there is a very obvious depression into the tissue with your finger, or you can very easily lift up a section of tissue between your thumb and fingers.

 

Issues that Can Result in Muscle Loss

There are a variety of conditions and diseases that can cause muscle loss. Anytime you suspect your pet has suffered muscle loss, a consultation with your veterinarian is essential.

  • Heart disease/failure
  • Chronic kidney disease
  • Diabetes
  • Cancer
  • Infiltrative and inflammatory bowel disease – inflammatory cells, such as lymphocytes, invade the lining of the intestines and prevent the absorption of nutrients
  • Severe intestinal parasitism
  • Organ failure – liver, kidney
  • Hyperthyroidism (more common in cats than dogs)
  • Protein-losing nephropathy – protein is lost from the body through the kidneys
  • Protein-losing enteropathy – protein is lost from the body through the intestines
  • Muscle disorders – masticatory myositis, muscle trauma, tumors, etc.
  • Medications, such as corticosteroids
  • Poor quality diet
  • Lack of activity due to injury or arthritis

dog and cat with muscle loss issues

How to Diagnose the Cause of Muscle Loss?

If your pet is on a good quality diet and they are eating, then it’s far more likely that their weight and muscle mass loss is due to one of the conditions in the list provided above, which means that a visit to your veterinarian is in order.

Being underweight for an extended time puts your pet at risk of compromised health and decreased quality of life. Underweight pets can become malnourished, immunocompromised, and have poor healing. Plus, they are at increased risk of physical injury, disease, organ failure, and more.

Your veterinarian will take a detailed history of your pet and perform a physical examination. Based on your pet’s history and the physical exam findings, they will recommend testing, which may include blood work (complete blood count), chemistry, urinalysis, fecal analysis, x-rays, ultrasound, specialized lab tests, and possibly others.

Once a diagnosis of the cause of the muscle loss is determined, your veterinarian will recommend a treatment plan tailored to your pet. Following their recommendations will help your pet’s recovery be more successful.

Remember, the sooner intervention occurs, the better the outcome. Starting from the time your pet is young, get them routine veterinary care, feed them a high-quality diet, maintain them at their ideal weight, provide regular exercise, and regularly perform body condition score (BCS) and muscle conditions score (MCS) checks.

To assess your pet's body score, use these charts:

Body condition chart for dogs

Body condition chart for cats

The ideal body score for your pet is 4 or 5 (on a 1 to 9 scale). When pets have a body condition score less than 3 they are getting too thin and bony.

About the author

Profile picture for Dr. Beth Turner

Dr. Beth Turner

Beth Turner is a veterinarian with over 20 years of experience. She graduated from North Carolina State College of Veterinary Medicine and following graduation, she began her career as an associate veterinarian and worked closely with the local shelter.

In 2007 she accomplished her dream of practice ownership, designing and building her own clinic. Another meaningful role, while running her clinic, was serving as her county's shelter veterinarian. This gave her the opportunity to help improve the lives of many animals in her community as well as work with the rescue she loved. She sold her practice in 2019 to move across the country.