Myasthenia gravis: Difference between revisions
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==Treatment== | ==Treatment== | ||
#Always evaluate tidal volume, FEV, negative inspiratory force, ability to handle secretions | |||
#Meds | |||
#*Pyridostigmine | |||
#**If pt's usual dose has been missed the next dose is usually doubled | |||
#**PO route: 60-90mg q4hr | |||
#**IV route: 1/30th of the PO dose (2-3mg) by slow IV infusion | |||
#*Neostigmine | |||
#**0.5mg IV | |||
#[[Intubation]] | |||
#*If possible avoid depolarizing AND non-depolarizing agents | |||
#**If pt requires paralysis use non-depolarizing agent at smaller dose | |||
#**If must use depolarizing agents, will need higher doses | |||
#Plasmapherisis | |||
#IVIG | |||
==See Also== | ==See Also== | ||
Revision as of 23:49, 19 July 2015
Background
- Autoantibody degradation, dysfunction, and blockade of acetylcholine receptor at the NMJ[1]
- Thymus is abnormal in 75% of pts
- Thymectomy resolves or improves symptoms in most pts, especially those with a thymoma
- No sensory, reflex, pupillary, or cerebellar deficits
Myasthenic Crisis versus Cholinergic Crisis
- Myasthenic Crisis
- Respiratory failure is feared complication
- Much more common
- D/t med non-compliance, infection, surgery, tapering of immunosuppressants, meds
- Cholinergic Crisis
- Excessive anticholinesterase medication may cause weakness and cholinergic symptoms
- Rarely if ever seen w/ dose limitation of pyridostigmine to less than 120mg q3hr
- If on usual dose of meds assume exacerbation due to MG even w/ cholinergic side effects
- Edrophonium (Tensilon) test to distinguish the two is controversial
- Give 1-2 mg IV slow push. If any fasciculations, resp depression, or cholinergic symptoms within a few minutes, problem is likely cholinergic crisis (no more edrophonium). If no evidence of cholinergic excess, give total of 10 mg and observe improvement in case of myasthenic crisis.
- Side effects of Edrophonium: Arrhythmias, Hypotension, Bronchospasm
- Treatment: Atropine
Clinical Features
- Symptoms worsen with repetitive use / as the day progresses[2]
- Ice Pack Test- should improve symptoms temporarily (usually ptosis; high specificity)
- Place ice-pack on eyes for 2 mins, if ptosis decreases by ≥2mm the test is positive
- Ice Pack Test- should improve symptoms temporarily (usually ptosis; high specificity)
- Muscle weakness
- Proximal extremities
- Neck extensors
- Facial/bulbar muscles (dysphagia, dysarthria, dysphonia)
- Ocular weakness
- Ptosis
- Diplopia
- CN III, IV, or VI weakness
Differential Diagnosis
Drug-induced myasthenia
- Antibiotics (aminoglycosides, fluroquinolones, clindamycin, metronidazole, macrolides)[3]
- Steroids
- Anticonvulsants (phenytoin, barbiturates, lithium)
- Psychotropics (haloperidol)
- Beta-blockers / calcium-channel blockers
- Local anesthetics
- Narcotics
- Anticholinergics (diphenhydramine)
- NMJ blocking agents (roc, sux)
Weakness
- Neuromuscular weakness
- Upper motor neuron:
- CVA
- Hemorrhagic stroke
- Multiple sclerosis
- Amyotrophic Lateral Sclerosis (ALS) (upper and lower motor neuron)
- Lower motor neuron:
- Spinal and bulbar muscular atrophy (Kennedy's syndrome)
- Spinal cord disease:
- Infection (Epidural abscess)
- Infarction/ischemia
- Trauma (Spinal Cord Syndromes)
- Inflammation (Transverse Myelitis)
- Degenerative (Spinal muscular atrophy)
- Tumor
- Peripheral nerve disease:
- Neuromuscular junction disease:
- Muscle disease:
- Rhabdomyolysis
- Dermatomyositis
- Polymyositis
- Alcoholic myopathy
- Upper motor neuron:
- Non-neuromuscular weakness
- Can't miss diagnoses:
- ACS
- Arrhythmia/Syncope
- Severe infection/Sepsis
- Hypoglycemia
- Periodic paralysis (electrolyte disturbance, K, Mg, Ca)
- Respiratory failure
- Emergent Diagnoses:
- Symptomatic Anemia
- Severe dehydration
- Hypothyroidism
- Polypharmacy
- Malignancy
- Aortic disease - occlusion, stenosis, dissection
- Other causes of weakness and paralysis
- Acute intermittent porphyria (ascending weakness)
- Can't miss diagnoses:
Treatment
- Always evaluate tidal volume, FEV, negative inspiratory force, ability to handle secretions
- Meds
- Pyridostigmine
- If pt's usual dose has been missed the next dose is usually doubled
- PO route: 60-90mg q4hr
- IV route: 1/30th of the PO dose (2-3mg) by slow IV infusion
- Neostigmine
- 0.5mg IV
- Pyridostigmine
- Intubation
- If possible avoid depolarizing AND non-depolarizing agents
- If pt requires paralysis use non-depolarizing agent at smaller dose
- If must use depolarizing agents, will need higher doses
- If possible avoid depolarizing AND non-depolarizing agents
- Plasmapherisis
- IVIG
See Also
Source
- ↑ Medications and Myasthenia Gravis (A Reference for Health Care Professionals) PDF
- ↑ Tintinalli's Emergency Medicine: A Comprehensive Study Guide, 7e (2010), Chapter 167. Chronic Neurologic Disorders
- ↑ Sanders DB, Guptill JT. Myasthenia Gravis and Lambert-Eaton Myasthenic Syndrome. Continuum. 2014 Oct;20(5)