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The underlying cause of the immune response against the acetylcholine receptors is not known but an association with thymomas and other [[Neoplasia - Pathology|neoplasia]] has been documented.

Myasthenia gravis is a disease of the neuromuscular junction that occurs due to a defect or absence of nicotinic acetylcholine receptors on the post-synaptic membrane (in the congenital form) or due to the presence of antibodies that bind to the receptors and prevent them from functioning normally (in the acquired form).  Acquired myasthenia Gravis is the most common form of the disease. The classical focal form of myasthenia gravis affects only the extraocular muscles, the cranial [[Oesophagus - Anatomy & Physiology|oesophagus]] and the muscles innervated by [[Cranial Nerves - Anatomy & Physiology|cranial nerves]] V, VII and IX.  90% of animals diagnosed with myasthenia gravis have [[Megaoesophagus|megaoesophagus]] at presentation.

Additionally immune mediated endocrinopathies such as [[Hypothyroidism|hypothyroidism]] and [[Hypoadrenocorticism|hypoadrenocorticism]] have also been associated with the disease.   

 

Acquired myasthenia Gravis is the most common form of the disease and cases present with generalized muscle weakness which is accentuated by mild exercise.

The focal form of myasthenia gravis affects only the extraocular muscles, the [[Oesophagus - Anatomy & Physiology|oesophagus]] and the muscles innervated by [[Cranial Nerves - Anatomy & Physiology|cranial nerves]] V, VII and IX.  Additionally 90% of animals diagnosed with myasthenia gravis have [[Megaoesophagus|megaoesophagus]] at presentation.

==Signalment==

==Signalment==

Acquired Myastehenia Gravis

'''Acquired Myastehenia Gravis''':

Akitas, German shorthaired pointers, Chihuahuas and some terrier breeds are predisposed to the disease, however Labradors and Golden retrievers are frequently diagnosed with the disease.

 

Dogs 2-3 years old and also older than 9 years old  are more commonly affected by the disease.

Akitas, German Shorthaired Pointers, Chihuahuas and some Terrier breeds are predisposed to the acquired Myasthenia Gravis, however, Labradors and Golden Retrievers are frequently diagnosed with the disease.

Dogs 2-3 years old and also older than 9 years old  are more commonly affected.

 

Abyssinian and Somali are the most commonly affected cat breeds and can be affected at any age.

English Springer Spaniels, Fox Terriers and Jack Russell Terriers are genetically predisposed to congenital Myasthenia Gravis, it has also been documented in Siamese and Domestic Short Haired cats.

English Springer Spaniels, fox terriers and Jack Russell terriers are genetically predisposed.

Has aso been documented in Siamese and Domestic short haired cats.

==Clinical Signs==

==Clinical Signs==

Acquired Myasthenia Gravis:

Three presentations of acquired Myasthenia Gravis have been reported.

three types of disease have been reported in the dog.

Focal disease and Generalized disease which can be acute or chronic in presentation.  

*Focal

*Generalized disease which can be acute or chronic in presentation.  

Animals affected with the focal form present with laryngeal, pharangeal, facial and oesophageal dysfunction.

Animals affected with the '''focal form''' present with laryngeal, pharyngeal, facial and oesophageal dysfunction.

Animals affected by the generalised form present in non-ambulatory tetraparesis often with dyspnoea. Of these dogs 90% will have concurrent megaoesophagus some of whom will have a history of regurgitation or aspiration pneumonia.

Animals affected by the '''generalised form''' present in non-ambulatory tetraparesis often with dyspnoea. Of these dogs 90% will have concurrent [[megaoesophagus]] some of whom will have a history of regurgitation or aspiration pneumonia.

Megaoesophagus does not occur as frequently in cats.  

Megaoesophagus does not occur as frequently in cats.

An association between thymomas and myasthenia has been made in both dogs and cats.

An association between thymomas and myasthenia has been made in both dogs and cats.

Congenital Myasthenia Gravis

'''Congenital Myasthenia Gravis''' presents with similar signs to the acquired form except that megaoesophagus is only rarely associated.

Presents with similar signs to the acquired form except that megaoesophagus is rarely found.

==Laboratory Tests==

==Laboratory Tests==

Acquired Myasthenia Gravis

'''Acquired''' Myasthenia Gravis:

Identifying serum antibodies for acetylcholine receptors is the test most commonly used to diagnose the disease.

 

Identifying '''serum antibodies for acetylcholine receptors''' is the test most commonly used to diagnose the disease.

Additionally the tensilon (edrophonium chloride) test can be undertaken where edrophonium chloride is given intravenously and an improvement is noted in affected patients which is demonstrated by increased muscle strength.

The '''tensilon (edrophonium chloride) test''' can also be undertaken where edrophonium chloride is given intravenously and an improvement is noted in affected patients which is demonstrated by increased muscle strength.

Also an ElISA is now available which identifies circulating antibody to the acetylcholine receptor.

Additionally an ELISA is now available which identifies circulating antibody to the acetylcholine receptor.

Congenital Myasthenia Gravis

'''Congenital''' Myasthenia Gravis

Autoantibodies are not present in this form of the disease as animals are born without the receptors. Diagnosis is based on the response to anticholinesterase treatment.

Autoantibodies are not present in this form of the disease as animals are born without the receptors and consequently diagnosis is based on the '''response to anticholinesterase treatment'''.

==Radiography==

==Radiography==

Lateral thoracic radiographs will often reveal megaoesophagus in dogs and a thymoma in cats.

Lateral thoracic radiographs will often reveal megaoesophagus in dogs and or a thymoma or other neoplastic mass in dogs and cats.

==Treatment==

==Treatment==

Anticholinesterase agents inhibit the cholinesterase enzyme breaking down acetycholine resulting in increases level and duration of the neurotransmitter in the synaptic cleft.

'''Anticholinesterase agents''' are the most common treament for Myasthenia Gravis. They inhibit the cholinesterase enzyme breaking down acetylcholine resulting in increased levels and duration of the neurotransmitter in the synaptic cleft.

Anticholinesterase agents include Pyridostigmine bromide and neostigmine

Anticholinesterase agents include pyridostigmine bromide and neostigmine.

 

Animals should be fed from a height and also have their head held in an elvated position for 5 minutes after feeding to avoid aspiration of food and the development of aspiration pneumonia.

Certain drugs including [[Aminoglycosides|aminoglycosides]] and antiarrhythmic drugs can interfere with neuromuscular transmission and should be avoided in myasthenia gravis patients.

The use of immunosuppressants in Myasthenia Gravis is documented but controversial, particularly in patients suffering from aspiration pneumonia.

Certain drugs including aminoglycosides and antiarrhythmic drugs can intefere with neuromuscular transmission and should be avoided in myasthenia gravis patients.

==Prognosis==

==Prognosis==

Animals suffering from acquired Myasthenia Gravis may be affected over a varied time span from months to years and animals can go into remission.

Animals suffering from acquired Myasthenia Gravis may be affected over a varied time span from months to years and animals can go into remission.

Animals with the congenital form do not go into remission and often deteriorate.

The prognosis also depends on the underlying cause of disease which may be neoplastic.

Animals with the congenital form have a poor prognosis they do not go into remission and often deteriorate.

 

==References==

==References==

[[Category:Antibody Mediated Autoimmune Diseases]]

[[Category:Antibody Mediated Autoimmune Diseases]]

[[Category:To Do - caz]]

[[Category:Immunological Diseases - Dog]][[Category:Neurological Diseases - Dog]][[Category:Musculoskeletal Diseases - Dog]]

[[Category:Dog]]

[[Category:Expert_Review]]

[[Category:Muscles - Developmental Pathology]][[Category:Muscles - Degenerative Pathology]]