Muscle Weakness in Dogs

Acetylcholine enables your dog’s muscles to receive and act upon nerve impulses that create movement. Lack of this neurotransmitter disrupts the communication channels between nerves and skeletal muscles causing generalised weakness. If your dog is born with this condition (congenital MG), it usually shows the effects between six to eight weeks of age.

Acquired myasthenia gravis can appear anytime. Dogs with muscle weakness become progressively weaker, they have problems standing up after they have been lying down, and they become tired easily. Exercise tends to make the symptoms worse.

Myasthenia gravis can be defined as muscle weakness. Affected dogs have abnormal numbers of functional receptors needed for a neurotransmitter known as acetylcholine.

Your pet's body weakness tends to get progressively worse although it comes and goes in cycles. Exercise can aggravate the condition. 

• Your dog will be unable to sustain active exercise and may even show reluctance to join in activities 
• Difficulty in swallowing demonstrated by needing several attempts to swallow
• Excessive drooling 
• Staggering, swaying gait - sometimes resulting in a sudden collapse 
• Breathing may vary in sounds, often being quite loud and strained 
• Coughing that is due to aspiration pneumonia 
• Your dog may sleep with its eyes open 
• Noticeable voice changes 

Types

• Congenital myasthenia gravis - Puppies born with too few acetylcholine receptors on the muscles, this condition is noticeable from six to eight weeks of age
• Acquired myasthenia gravis can affect small dogs usually around 1 to 4 years of age or after nine years; larger dogs tend to become affected a bit earlier
• Myasthenia gravis is classified as an autoimmune disease
• Three further categories for acquired MG are mild or focal, involving only one body part (for example, the esophagus), moderate (limb weakness with or without megaesophagus) and severe (rapid progression and usually fatal)
• This condition can affect both male and female dogs

• The cause of myasthenia gravis is produced by a reduction in cellular receptors for the neurotransmitter acetylcholine at the connection between nerve endings and where the skeletal muscle cells join 
• Muscle weakness caused by the condition is a disorder resulting from a breakdown of communication between the delivery of impulses from the nerves to the muscles 
• Without proper communication between the nerves and muscles your dog will become weak as their muscles are not contracting correctly and the muscles become weakened 
• If your dog suffers from cancer (especially thyroid gland tumors), Addison’s disease or low circulating levels of platelets they are more likely to develop acquired myasthenia gravis as they age
• Muscles around the muscles that assist with eating (mastication) can also be affected, and your dog will find chewing and swallowing to be difficult 
• Congenital myasthenia gravis is considered by experts to be a partly hereditary condition 
• The muscle weakness is aggravated by exercise and relieved by rest

A typical symptom of muscle weakness in dogs is your companion displaying severe weakness after only a short period of exercise. Muscle tremors and an awkward, stiff gait are another sign that all is not right. As myasthenia gravis can affect the muscles of your dog’s throat, signs such as regurgitating food and water, drooling and difficulty swallowing should send you to visit your veterinarian to have your dog assessed for this condition. The acquired form affects Terrier breeds, German Shepherds, Golden Retrievers and German Shorthaired Pointers. The congenital form affects  Jack Russell Terriers, Springer Spaniels, and others. 

Your veterinarian can administer a blood test to detect any antibodies aimed at the acetylcholine receptor. Another test, called the Tensilon test, where your dog will get a short acting antidote that boosts the effects of acetylcholine on the muscle, will also be done. In patients that have myasthenia gravis, there will be a sudden increase in muscle strength after the injection that will have your dog up on his feet and even running around. Unfortunately, the effects wear off after only a few short minutes.  

Other tests include an electromyogram (EMG) to deliver electrical stimulation to individual nerves or muscle of an anesthetised animal. How well these react to the stimulation helps to diagnose the severity of the condition. X-rays of the chest area may be done to rule out cancer which can trigger myasthenia gravis. These x-rays will also help evaluate the esophagus condition and detect pneumonia caused by food particle inhalation.

While there is no cure or preventative measures for this disease, there is treatment through medication and a high level of care that will enable your dog to maintain a quality of life for a long time. Your dog will be admitted to hospital if his condition is severe. If your dog has aspiration pneumonia or is unable to eat or drink without bringing it all back up again, then the hospital will be required to stabilise the condition. Treatment of pneumonia includes intensive injections and oral antibiotic therapy, placement of an intravenous catheter and supportive nursing care along with intravenous fluids. If your dog cannot retain his food, a gastrostomy tube will be carefully placed to allow nutrition and hydration to occur.

There are several drugs that are used to concentrate the action of acetylcholine at the neuromuscular junction sites. These medications are anticholinesterase drugs and are administered either orally or via injection. These drugs help to build up the muscle strength by reducing your dog’s antibodies attack on the muscle receptors which allows the muscles to work unhindered. Corticosteroids may be needed as treatment as well. Keeping your dog’s head elevated will help their food go down. Preventing aspiration pneumonia is vital to allow your dog to recover. Ensuring your dog’s head remains elevated during feeding and for approximately 15 minutes afterwards will help.

The outlook with treatment is good, although care must be taken to avoid severe secondary pneumonia due to the inhalation of food material. Treatments for this condition can last many months with constant monitoring to check on improvements in health will be required by your veterinarian. Regular blood tests will also need to be done to measure the levels of antibodies against the acetylcholine receptors.

Muscle weakness is a debilitating disease, but early diagnosis and a high level of care given to your pet can control the symptoms allowing your dog a full and active life. Full recovery is possible but depends on quick diagnosis and administration of prompt treatment.