Myasthenia gravis, an autoimmune disorder affecting the myoneural junction, is characterized by varying degrees of weakness of the voluntary muscles. Women tend to develop the disease at an early age (20-40 yrs of age) In men (60-70 yrs of age)
Ocular muscle – diplopia (double vision) Ptosis (drooping of the eyelid)Major signs and symptoms Bulbar symptom- weakness of the muscle of face and throat Generalized weakness- resulting decrease vital capacity and respiratory failure Dysphonia (voice impairment)- this may result increase risk for choking and aspirationMyasthenia gravis is purely a motor disorder with noeffect on sensation or coordination.
Myasthenic crisis Cholinergic crisis
is an exacerbation of the diseaes process. Crisis may result from disease exacerbation or a specific precipitation event.Most common precipitator is infection; medicattion change, surgery, pregnancy and high environmental temp.Symptoms Severe generalized muscle weakness and respiratory And bulbar weakness that may result respiratory failure
Symptoms of anticholinergic overmedication may mimic the symptoms of exacerbation Differentation can be achieved with the edrophonium chloride (tensilon) test.Difference between myasthenic & cholinergicMyasthenic- improves immediately following adminstration of edrophoniumCholinergic- crisis may experience no improvement or deteriorate
Myasthenic crisis – neostigmine methylsulfate, prostigmine is admin IM or IV until the pt. is able to swallow oral anticholinestrase meds.-plasma pheresis and IVIG- reduce antibody loadCholinergic crisis – all anticholinestrase meds should be stop- Atrophine sulfate should be given- an antidote for anticholinestrase medication.
Anti cholinestrase test Edrophonium chloride (tensilon) injected through IV- 2mg at a time to a total of 10mg (30sec after injection, facial muscle weakness & ptosis should resolve for about 5min=+). Atrophine (o.4mg)should availabale for side effects. Repetitive nerve stimulation test- it records the electrical activity in target muscle after nerve stimulation. MRI- for enlarged thymus gland
Administration of anticholinestrase agent Pyridostigmine bromide (mestinon) & neostigmine bromide (prostigmine)Effect: provide symptomatic refief by increasing the relative concentration of available acetylcholine at the neuro muscular junction. Improve strength and less fatigueImmunosuppresive therapy CorticosteroidsEffect: to reduce production of the antibodyPrednisone taken on alternate days to lower the incidence of side effects.
Plasmapheresis- blood cells & antibody containing plasma are separated, then cells and plasma substitutes are reinfused.Effect: plasma exchange used to treat exacerbations. The improvement may last only a few weeksIV immune globulin – nearly effective as plasmapheresis in controlling symptoms exacerbation. Thymectomy - it can decrease or eliminate the need for medication