Myasthenia Gravis in Dogs

Myasthenia Gravis, also abbreviated MG, is a neuromuscular disease found in dogs. The chief cause of the condition is discovered to be anomalous transmission of information between nerves. This happens due to decrease in the number of receptors of a certain chemical which is essential for transmission. These are the neurotransmitter called acetylcholine.

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Every muscle in the body is regulated by its own nerve; however, this does not have direct link with the muscle. There are actually small gaps in the ‘neuromuscular junctions’, these are the junctions between muscles and nerves. The signals along the nerve are transmitted in the form of electrical current. When these electrical current reaches the end of the nerve at the junction the signals must be passed across this gap.

There is a chemical messenger called acetylcholine which serves as the bridge through this gap. This messenger is secreted from the end-point of the nerve, traverses across the gap and gets attached to specific acetylcholine receptor of the muscle. The acetylcholine links to the receptor as a key fits to its lock. It then stimulates signals that lead to muscles contraction. When myasthenia gravis affects a dog the remission of message between muscles and nerves becomes abnormal and inappropriately transmitted.

If contraction of muscles becomes abnormal then the muscles may becomes weak. Weakness of the muscles can include the limbs and unable the affected dog from standing or exercising, etc. The condition may also affect other muscles in the body of the animal. The muscles associated with the pipe that transfers food from mouth into the stomach, also called oesophagus stomach, are usually weak in dogs affected with Myasthenia Gravis. This is why affected dogs may face difficulties swallowing food and may often throw it out after eating. In serious cases muscles associated with breathing may also become affected.

There are two types of MG recorded in dogs which are congenital and acquired. Congenital MG is one that is present in the animal since birth while acquired is the one which is developed later in lifetime.  Out of the two acquired type of MG is said to be common. This type of MG is seen in breeds such as Akitas, German shorthaired pointer, golden retriever, German shepherd dog, etc. Congenital MG is rarely recorded and is present in breed such as Springer Spaniels, fox terriers, etc.

Myasthenia Gravis dog

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Causes 

Dogs with congenital Myasthenia are born with little acetylcholine receptors. The acquired type of MG is said to occur due to defected immune-system. Immune system is responsible for protecting the body from invaders that do not belong to the body. Production of antibodies can help the immune system to protect the body. In case of acquired myasthenia gravis the antibodies produced by immune system attacks acetylcholine receptors. It is not determined why such occurrence takes place in dogs’ body. MG can be caused due to cancer in some cases. It may also be associated with underlying immune system diseases or with hypothyroidism. Irrespective of the cause acetylcholine will not be able to get restored to normal health if receptors are anomalously low.

Symptoms of Myasthenia Gravis

The most common core of symptoms experienced in case of Myasthenia Gravis is weakness of muscles. Affected dog may suffer from muscles weakness at different regions such as eyes, facial muscles, throat, limbs, esophagus, etc. This may cause early and easy exercise fatigue. This is recorded in 60% of affected dogs. Dogs may also find it difficult to swallow food and may throw it out after eating. Symptoms of MG may develop in days or weeks and may be broad spectrum. Signs associated with this condition may vary greatly from one dog to another. However, in dogs the prognosis is usually good if they manage to survive the first month of affliction. This is because weakness is severe during the first month. The treatment of the condition can be long-running. In some cases wherein tumors are also recorded the dog may have to be surgically treated.

Diagnosis

Simple blood test can help in evaluating antibodies against these acetylcholine receptors. This test is also known as AChR test. This is the test that can detect around 98% cases of Myasthenia Gravis in dogs. When the count of antibodies is less than 0.6 nmol/L symptoms associated with it generally resolves. However, this test can be done only in one laboratory in San Diego, US. Thus it can prove to be expensive and may take a couple of weeks to obtain results. .

Tensilon Test is another tentative way of diagnosing the condition. In this test endrophonium chloride injection is given to the affected dog. The reaction of this substance can be seen in a video output. This is in fact a quick way of diagnosing MG.  Few other tests that can help in determining the prevalence of Myasthenia Gravis include tissue biopsy, chest radiography, etc.

 Treatment for Myasthenia Gravis

With early diagnosis and appropriate treatment the condition can be dealt with successfully and the affected dog may also regain normal life expectancy. The treatment for MG in case of acquired form is greatly depended on medicines that can decrease breakdown of acetylcholine. This allows longer time for neurotransmission. One of the most commonly used and primary canine medicine is Mestinon or Pyridostigmine hydrochloride.  In order to determine an effective and suitable dosage, adjustments may be done consistently.  In case of the congenital MG same drugs are used but puppies do not respond well to the drug. Unfortunately if there is no improvement and condition becomes worse the pups may have to be euthanized.

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