Myasthenia Gravis In Dogs

Myasthenia gravis (MG) is a rare, autoimmune, or acquired neurological disorder affecting transmission at the neuromuscular junction. Specifically, Myasthenia gravis is an abnormality in the transmission of information from one nerve to another due to a decrease in the number of receptors for a neurotransmitter (acetylcholine) crucial to this transmission.

Myasthenia Gravis literally means muscle (my-), weakness (asthenia), grave (gravis) - grave muscle weakness. The core clinical manifestation of Dogs with myasthenia gravis is extreme muscle weakness and excessive fatigue. The condition may affect bulbar, ocular, limb, and respiratory muscles. This connection of respiratory musculature in MG can lead to a serious crisis.

Two forms of MG are documented in veterinary medicine: The congenital MG (a disease that the dog is born with) carries a very poor prognosis. This happens when dogs from birth itself have a reduced number of acetylcholine receptors.

The acquired version is thought to be a less threatening disease in which the dog’s own immune system mistakenly attacks its own acetylcholine receptors, as a threat (cause unknown) thereby thwarting normal nerve communication.

Eye muscles

• Weakness of the eye muscles (ocular myasthenia)
• Drooping of one or both eyelids (ptosis)
• Double or blurred vision (diplopia)

Face and throat muscles

• Impaired sounds
• Cause difficulty swallowing (dysphagia)
• Chewing problems
• Change facial expressions

Neck and limb muscles

• Cannot hold up the head (Weak neck muscles)

Respiratory and GI symptoms:

• Wretching
• Regurgitating (Megaesophagus)
• Coughing (aspiration pneumonia)
• Difficulty breathing (aspiration pneumonia)

Nervous system:

• Absent or decreased blink reflex
• Spinal reflexes are normal but maybe fatigued
• Absent or decreased gag reflex

Other symptoms:

• Overall weakness
• Inability to walk properly/Falling
• Inability to stand/ move for long periods of time
• The desire to rest rather than exercise and move around

Anti-acetylcholinesterase medications: Pyridostigmine bromide (brand name Mestinon)

This drug enhances the availability of acetylcholine and so boosts muscle activation and contraction. Depending on individual circumstances, it may be essential to give immunosuppressive drugs that will suppress the immune system to discontinue attacking the receptors.

Megaesophagus: Elevated feeding techniques are used to minimize the effects of gravity.

Pneumonia: Antibiotics will be given, if the condition worsens, oxygen therapy, IV fluid therapy, and supportive care will be recommended.

For dogs that do not experience severe aspiration pneumonia or difficulty swallowing and weakness of the throat, the prognosis is good for complete recovery within 5-6 months.

Better the prognosis for your dog, if more attention is paid to the prevention of aspiration pneumonia.

Physical therapy: Massage can help relieve the dog’s sore muscles.

Proper treatment and careful home care can help dogs with myasthenia gravis maintain a quality of life for a reasonably long time.

Prevention is not possible for MG. Treatment and survival rates vary depending on the grade and stage of the muscle weakness.

Good overall health and early detection are the only ways to prevent MG.

Check your dog on a regular basis and consult your veterinarian immediately if you find any eye muscle defects and/or inability to walk properly or fall frequently.

Jack Russell Terrier, Springer Spaniel, Smooth Fox Terrier, German Shepherd, Golden Retriever, Labrador Retriever, Puppies, Senior Dogs

Causes:

• Congenital (present at birth)
• Autoimmune disorder
• Secondary to cancer

Types:

Congenital MG: This is an inherited autosomal recessive trait characterized by muscle weakness (myasthenia) and is seen in puppies.

Acquired MG: An autoantibody-mediated obliteration of acetylcholine receptors (AChR) at the postsynaptic side of the neuromuscular junction causes MG for reasons unknown. It’s most prevalent among middle-aged to older dogs.

Clinical forms of myasthenia gravis:

Ocular MG: Symptoms are restricted to eye muscles and eyelid movements. About 15 percent of dogs with MG have the ocular form

Generalized MG: Muscles of the face, legs, and arms are most affected

Transient neonatal MG: Some puppies born to dogs with MG will have temporary muscle weakness due to transplacental transfer of maternal autoantibodies against the acetylcholine receptor (AChR). This automatically wears off after a few weeks.

Morbidity:

• The most common presentation: generalized MG symptoms account for 60% of cases.
• Focal presentation: There may be a weakness of a particular muscle group and this accounts for about 30 - 35% of cases. Commonly affected muscles include the facial muscles (decreased palpebral reflex), laryngeal/ pharyngeal muscles (leading to loss of bark and/or dysphagia ), or esophagus (leading to megaoesophagus).
• The least common presentation: The fulminating form and these account for the remaining 5-10% of cases. This form presents with an acute, non-ambulatory quadriparesis with decreased spinal reflexes and decreased muscle tone. These dogs often have sudden onset of megaesophagus and facial nerve weakness.

Mortality:

Most of the cases have a normal life span Even in moderately severe cases; most dogs can continue to live comfortably with treatment. The life expectancy of MG dogs is normal except in rare cases.

Diagnosis:

• Blood testing for antibodies associated with MG
• Repetitive nerve stimulation test
• Edrophonium chloride test: Tensilon (or a placebo) is a short-acting anticholinesterase administered intravenously, and the dog is made to perform muscle movements under vet observation.
• MRI or CT scans to rule out a tumor
• ACh receptor autoantibody test:

This test is the gold standard test for diagnosing MG. The possibility to get a false negative result in 2% of generalized cases (seronegative).

Prognosis:

Myasthenia Gravis can be very mild to severe. The outcome is typically good for a complete recovery unless severe difficulty eating or the presence of cancer or severe pneumonia.

MG Treatment in dogs usually lasts for months. Your vet will periodically re-examine the pet on a regular basis to check for improvements. Regular blood tests will be performed to determine anti-AChR antibody levels.

Even in severe cases, early diagnosis, and with appropriate treatment, your pet may make a full recovery.

Contact your vet right away, if you notice any of the following:

• Signs of pneumonia, include cough, decreased appetite, and lethargy.
• Weakness of the eye muscles (ocular myasthenia)
• Drooping of one or both eyelids (ptosis)

Foods to avoid:

• Avoid fatty foods or high in fiber
• Cutback on greasy, oily, spicy foods
• Avoid crunchy or chewy snack foods
• Avoid dairy products like milk, yogurt, etc
• Bread products and roasted nuts
• Avoid tougher meats

What to feed:

• Smaller, more frequent meals of a high-quality, high-calorie food
• Choose softer foods such as mashed, soft, or pureed foods
• Moisten/soften foods with chicken broth, gravy, or butter
• Finely chop up veggies, chicken, or meat.
• Watch the salt intake of dogs such as from canned soups or frozen meals.
• Add calcium-rich foods and supplements such as like broccoli, salmon, Sardines, and Dark leafy greens.

Although MG is treatable, most pets require months of medication and special feeding.

Pet owners should remember that it is a progressive condition and we can try to slow the progression.

With the right supportive care and medications, pets can live a longer, quality life.