Myasthenia Gravis Flashcards
Myasthenia Gravis is:
- charaterized by severe muscle weakness
- autoimmune disorder
- antibodies are produced agianst the nicotinic receptors
Symptoms of Myasthenia Gravis:
muscle weakness is:
- aggravated by exercise, but improved by rest
- usually less evident on awakening and get worse as the day progresses
Myasthenia Gravis in the Oculomotor muscles
- double vision (diplopia)
Myasthenia Gravis in the Elevator muscles of the eye lid
- lid drooping (ptosis)
Myasthenia Gravis in Oropharyngeal muscles
- difficulty swallowing
Myasthenia Gravis in Facial muscles
- difficulty speaking, and smiling
Myasthenia Gravis in Trunk and Limb muscles
- diaphragm becomes weak (major concern)
Seropositive Myasthenia Gravis
- antibodies to nicotinic receptors in the serum
Seronegative Myasthenia Gravis
- antibodies against muscle-specific kinase (MuSK) (membrane signalling element)
OR - a mutation in Rapsyn (a membrane signalling protein) - NOT autoimmune
OR - congenital due to an inherited deficiency in ACh receptors - NOT autoimmune
Diagnostic tests for Myasthenia Gravis
- Musclar Power test
- Edrophonium (Tensilon) test
- Give tubocurarine at 1/20 the usual therapeutic dose
- Detection of circulating antibodies to AChR, and MuSK
- Measure ACh receptor density from a muscle biopsy (uses radiolabelled alpha-bungarotoxin)
Edrophonium (Tensilon) Test
- it is a short acting acetylcholinesterase inhibitor
- given iv
- positive if there is a marked increase in muscle strength within 1 minute
Only identifies a defect in neuromusclar transmission
Tubocurarine at 1/20 therapeutic dose test
- positive if it decrease muscle strength
Only identifies a defect in neuromuscluar transmission
Antibody test
- finds the cause of muscle weakness
- best diagnostic test
Drug Treatment options
- Oral Acetylcholinesterase inhibitors
- Corticosteroid therapy
- Immunosuppresive drugs
- Plasms Exchange
- Intravenous Immunoglobulin Infusion
- Thymectomy
oral acetylcholinesterase inhibitor
Pyridostigmine (Mestinon)
Prednisone
Corticosteroid
Corticosteroid Therapy
- used for patients with myasthenia gravis confined to eye muscles or generalized muscle weakness
- used for patients who do not respond to conventional treatments
- titrated dose
- when remission is acheived dose is slowly lowered to the effective minimal dose
Adverse effect of Corticosteroid therapy
- weight gain, cataracts, diabetees, insomnia, mood change (depression), and osteoporosis
Depression with Myasthenia Gravis
- depression can be mistaken for Myasthenia Gravis
- during corticosteroid therapy dose will be increased, but increasing the dose will worsen the depression
- then around we go
Immunosuppressive drugs
Azathioprine Cyclosporine Cyclophosphamide - global decrease in immune repsonse - for the most serious or resistant cases
Plasma Exchange (Plasmapheresis)
- removes circulating antibodies
- separation of blood cells from plasma cells
- only temporary improvement
- used for myasthemic crisis
Myasthenic Crisis
- Severe Muscle Weakness event
- severe and sudden exacerbation of the existing disease
- affect on breathing is the main concern
Intravenouse Immunoglobulin Infusion
- treatment for myasthemic crisis
Thymectomy
- removal of the thymus gland in cases of tumor
- option for moderate to severe seropositive myasthenia gravis who are inadequately controlled by drug therapy
- for patients under 45
- miximum improvement occurs in the first year after surgery
