@Autoimmune disorder in which antibodies (Ab) against acetylcholine [Ach] receptors at motor end plates in NM junction.
@ Ab production by B cells defectively regulated by T lymphocytes
@ increased incidence in thymoma pts
C/F
@ Age- 15 to 50 yr
@ females more affected
@ easy fatiguability with muscle paresis
@ reflexes, sensations normal
@ diurnal variations present
@ ocular muscles most commonly affected resulting in Ptosis n diplopia. Pupils not involved
@ bulbar muscle Involvement results in dysphagia, nasal regurgitation n nasal twang
@ proximal Limb muscles involved - difficulty in raising hand above head n problems in getting up 4m squatting or sitting positions
@ involvement of respiratory muscles results in myasthenic crisis can cause death
Myasthenic crisis
@ in pts with MG not on any Rx or drug resistant
Cholinergic Crisis
@ Result of relative overdose of anticholinesterases drugs presents with diarrhea excessive salivation n lacrimation, resp insufficiency urinary incontinence
Investigations
# Tensilon (edrophonium) test
@ it is anticholinesterase inhibitor short duration action
@ 2 mg as test dose followed by 8mg results in dramatic improvement in symptoms within 30 sec n persists up to 1 to 2 minute suggestive of MG
# Others
@ CXR n CT 4 thymic enlargement
@ thyroid function test [10% postive]
@ Ach receptor Ab levels [in > 90% pts]
@ Anti muscle specific protein kinase Ab
@ nerve conduction test, repititive nerve stimulation, exercise testing, single fiber EMG
@ Ice test
patients with ptosis small cube of had placed over eyelid 4 2 min - improvement suggest disease
Management
# Anticholinesterase
@ neostigmine (15mg) or pyridostigmine (75mg) 3 to 6 times a day
side effects like abdominal cramps managed with propantheline 15 mg BD or tds
# Steroids
# Thymectomy
# Immunosuppression by azathioprine cyclophosphamide mycophenolate
# Plasmapheresis n IV Ig 4 short term remission
# Supportive measures
ventilatory assistance n nasogastric tube
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