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A chronic disorder of the neuromuscular junction that interferes with the chemical transmission of acetylcholine between the axonal terminal and the receptor sites located in the muscle cell membrane.
myasthenia gravis
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cause of myasthenia gravis is
unknown
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Loss of function of acetylcholine receptors on muscle cell membrane (sarcolemma) results in muscle weakness and potentially
paralysis in a descending pattern (think Mind to Ground)
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Myasthenic crisis refers to exacerbation of symptoms that result in
respiratory impairment
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Symptoms improve with administration of what type of drugs
anticholinesterase drugs
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clinical signs of myasthenia gravis is slow to abrupt onset- weakness of the
facial muscles, particularly of the eyelids
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drooping of the eyelids
ptosis
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tongue and laryngeal muscles may also be affected- 2 types of impairs
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Progression of weakness moves from
upper to lower extremeties
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Short-acting anticholinesterase drug
10 mg is injected via IV while areas of major muscle weakness are observed
Muscle weakness will resolve within 20-30 seconds and remain nearly normal for a few minutes if MG is the cause of the patient’s weakness
tensolin test
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Confirm the diagnosis
Identify the muscles involved
Determine the degree of fatigability
Electromyography
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Presence of thymoma by:
- Computed tomography (CT) scan
- Magnetic resonance imaging (MRI) scan
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Pulmonary function testing
- Decrease in volumes and expiratory flows
- Obstructive AND Restrictive pattern
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Arterial blood gases
- Respiratory acidosis (↓pH, ↑PCO2)
- Acute ventilatory failure
Hypoxemia
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Inhibit the function of cholinesterase, increasing the concentration of acetylcholine to compete with the circulating anti-acetylcholine antibodies, which interfere with the ability of acetylcholine to stimulate the muscle receptors
Tensilon (edrophonium chloride)
Cholinesterase inhibitors
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Prostigmin (neostigmine)
-Overuse may result in a cholinergic crisis, which is characterized by
increasing muscle weakness and which, through involvement of the muscles of respiration, may result in death
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due to an increase in the severity of the disease, is also accompanied by extreme muscle weakness, and thus may be difficult to distinguish from cholinergic crisis on a symptomatic basis
what type of chrisis
Myasthenic crisis
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Corticosteroids
Prednisone
Cyclophosphamide (Cytoxan, Neosar)
Azathioprine (Imuran)
are what type of drugs
immunosuppresents
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Administration of adrenocorticotropic hormone (ACTH)
is what type of therapy
Adrenocorticotropic Hormone Therapy
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removal of the thymus
Tymectomy
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Replacing patient’s plasma with human processed plasma (human albumin)
Plasmapheresis
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But what is our role? - Respiratory Therapy
- Vital capacity (VC)
- Normal is 60-80ml/kg
- <10 ml/kg = impending ventilatory failure
Negative inspiratory force (NIF) or maximal inspiratory pressure (MIP)
Measurement greater than -20 to -30 cmH2O usually indicates severe weakness of the inspiratory muscles
- Oxygen therapy
- Bronchopulmonary hygiene therapy
- Hyperinflation therapy
- Mechanical ventilation if patient clinically demonstrates impending or acute ventilatory failure (↓pH, ↑PCO2)
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