MG Flashcards
epidemiology and definition?
more common in females between 20-40 yrs old. autoimmune neuromuscular junction disorder
pathophysiology and associated conditions?
autoantibodies against post-synaptic acetylcholine receptors at NMJ. associated with thymoma and other autoimmune diseases (thyroid, SLE, RA)
classifications? seropositive vs seronegative MG?
ocular MG: involving eye muscles
generalized MG: involving all skeletal muscles ocular, limbs, bulbar, respiratory (NOT HEART).
seropositive means present antibodies against AchR.
seronegative means antibodies against AchR aren’t present but anti-musk can be positive
clinical features?
DESCENDING FATIGUABLE WEAKNESS of skeletal muscles, worse with use better with rest.
eyes: ptosis, blurry vision, diplopia
bulbar: dysarthria, dysphagia
respiratory: dyspnea, respiratory failure
proximal muscles: weakness (difficulty standing from chair, brushing hair, climbing stairs)
NORMAL REFLEXES AND REACTIVE PUPILS.
simpson test: looking up for >1 minute produces eyelid fatigue
exacerbating factors for MG?
diagnosis?
infections, surgery, pregnancy
diagnosed by detection of antibodies or EMG.
test for AchR antibodies or anti-musk (if seronegative)
EMG will show decremental response with repetitive nerve stimulation
chest CT: to find thymoma
DDx?
lambert-eaton: autoimmune NMJ disorder with autoantibodies against presynaptic voltage gated calcium channels. ASSOCIATED with small cell cancer
present with ASCENDING PROXIMAL MUSCLE WEAKNESS that IMPROVES with use. also with autonomic symptoms (dry mouth, constipation)
diagnosed with detection of antibodies, EMG showing incremental response, and lambert sign (hand grip strength improves after several seconds)
treated with amifampridine (blocks presynaptic potassium channels, increase AP duration and Ca concentrations)
treatment and MG crisis?`
treated with acetylcholine esterase inhibitors (pyridostigmine). can add steroids if inadequate symptom control. Thymectomy.
MG crisis is acute exacerbation of MG that can lead to respiratory failure and death. must differentiate from cholinergic crisis. treated with prednisone and IV Ig or plasma exchange
MG crisis vs cholinergic crisis?
both present with muscle weakness, SOB, sweating, agitation, disorientation, drowsiness.
cholinergic: miosis, bradycardia, warm flushed skin, present fasciculations
MG crisis: normal pupil, no sweating, cold skin, tachycardia, no fasciculations
