Internal Medicine

0521779407-14 CUNY1086/Karliner 0 521 77940 7 June 4, 2007 21:16

1026 Myasthenia Gravis

■Electrophysiologic studies to detect impaired neuromuscular trans-

mission

■Assay of serum acetylcholine receptor antibody & muscle-specific

tyrosine kinase (MuSK) antibody levels

differential diagnosis

■Drug-induced myasthenia is distinguished by history of use of causal

agent

■Pattern & variability of weakness distinguishes myopathies, motor

neuropathies, motor neuronopathies

management

■Assess severity of disease & adequacy of ventilation; provide venti-

latory support as needed

■Avoid or replace meds interfering w/ neuromuscular transmission

(eg, aminoglycoside antibiotics, beta blockers, calcium channel

blockers, magnesium salts)

specific therapy

■Anticholinesterases (eg, pyridostigmine) may relieve or reduce

symptoms; dose has to be individualized; overmedication enhances

weakness

■Steroids often helpful when response to anticholinesterases is poor,

but may lead to initial worsening of symptoms; dose is individual-

ized, but initial high dose is tapered to lower maintenance dose

■Azathioprine or mycophenolate mofetil may be helpful if above mea-

sures are inadequate

■Thymectomy may lead to remission

■Plasmapheresis or IV immunoglobulins often helpful for major or

acute disability, or prior to thymectomy

follow-up

■Regular follow-up needed to avoid complications & ensure optimal

therapy

complications and prognosis

■Involvement remains purely ocular in 20% of cases

■Disorder may worsen during systemic infections, thyroid disease,

pregnancy or w/ drugs affecting neuromuscular transmission

■Thymoma is present in 10–20% of pts & is assoc w/ more severe

disease

■Avoid inhalational anesthesia if possible; avoid or use neuromuscu-

lar blockers w/ great care