Difference between revisions of "Myasthenia Gravis"
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| − | + | ==Description== | |
| − | + | 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. | |
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| − | Acquired myasthenia Gravis is the most common form of the disease | ||
| − | 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. | ||
==Signalment== | ==Signalment== | ||
| − | + | Acquired Myastehenia Gravis: | |
| − | Akitas, German | + | 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. | 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 | + | Abyssinian and Somali are the most commonly affected cat breed and can be affected at any age. |
| − | + | Congenital Myasthenia Gravis: | |
| − | English Springer Spaniels, | + | 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. |
| + | ==Diagnosis== | ||
==Clinical Signs== | ==Clinical Signs== | ||
| − | + | Acquired Myasthenia Gravis: | |
| − | Focal | + | three types of disease have been reported in the dog. |
| + | *Focal | ||
| + | *Generalized disease which can be acute or chronic in presentation. | ||
| − | Animals affected with the | + | Animals affected with the focal form present with laryngeal, pharangeal, facial and oesophageal dysfunction. |
| − | Animals affected by the | + | 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. |
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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 | |
| + | Presents with similar signs to the acquired form except that megaoesophagus is rarely found. | ||
==Laboratory Tests== | ==Laboratory Tests== | ||
| − | + | Acquired Myasthenia Gravis | |
| − | + | Identifying serum antibodies for acetylcholine receptors is the test most commonly used to diagnose the disease. | |
| − | Identifying | ||
| − | + | 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. | |
| − | + | Also an ELISA is now available which identifies circulating antibody to the acetylcholine receptor. | |
| − | + | Congenital Myasthenia Gravis | |
| − | Autoantibodies are not present in this form of the disease as animals are born without the receptors | + | 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. |
==Radiography== | ==Radiography== | ||
| − | Lateral thoracic radiographs will often reveal megaoesophagus in dogs and | + | Lateral thoracic radiographs will often reveal megaoesophagus in dogs and a thymoma in 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 include | + | Anticholinesterase agents include Pyridostigmine bromide and neostigmine |
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| − | + | Animals should be fed from a height and also have their head held in an elevated position for 5 minutes after feeding to avoid aspiration of food and the development of aspiration pneumonia. | |
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| − | + | Any accompanying megaoesophagus must also be treated appropriately. | |
| + | Certain drugs including [[Aminoglycosides|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. | |
| − | Animals with the congenital form | ||
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==References== | ==References== | ||
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[[Category:Antibody Mediated Autoimmune Diseases]] | [[Category:Antibody Mediated Autoimmune Diseases]] | ||
| − | [[Category: | + | [[Category:To Do - Caz]] |
| − | + | [[Category:Dog]] | |
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Revision as of 08:48, 17 August 2010
 |
This article is still under construction. |
Description
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 and the muscles innervated by cranial nerves V, VII and IX. 90% of animals diagnosed with myasthenia gravis have megaoesophagus at presentation.
Signalment
Acquired Myastehenia Gravis:
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 breed and can be affected at any age.
Congenital Myasthenia Gravis:
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.
Diagnosis
Clinical Signs
Acquired Myasthenia Gravis: three types of disease have been reported in the dog.
- 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 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. An association between thymomas and myasthenia has been made in both dogs and cats.
Congenital Myasthenia Gravis Presents with similar signs to the acquired form except that megaoesophagus is rarely found.
Laboratory Tests
Acquired Myasthenia Gravis 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.
Also an ELISA is now available which identifies circulating antibody to the acetylcholine receptor.
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.
Radiography
Lateral thoracic radiographs will often reveal megaoesophagus in dogs and a thymoma in cats.
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 include Pyridostigmine bromide and neostigmine
Animals should be fed from a height and also have their head held in an elevated position for 5 minutes after feeding to avoid aspiration of food and the development of aspiration pneumonia.
Any accompanying megaoesophagus must also be treated appropriately. Certain drugs including aminoglycosides and antiarrhythmic drugs can intefere with neuromuscular transmission and should be avoided in myasthenia gravis patients.
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 with the congenital form do not go into remission and often deteriorate.
References
Ettinger, S.J. and Feldman, E. C. (2000) Textbook of Veterinary Internal Medicine Diseases of the Dog and Cat Volume 2 (Fifth Edition) W.B. Saunders Company