Neuromuscular Disorders Flashcards
how do motor neurones supply muscles?
via the NMJ
presynaptic NMJ disorders
- curare
- botulism botox
- Lambert Eaton Myasthenic Syndrome (LEMS)
postsynaptic NMJ disorders
myasthenia gravis
what is curare?
dangerous toxin used in hunting that occupies AChR and does not open ion channel so no muscle contraction (no respiration)
where is botulism toxin found?
soil
food
wounds (infected)
IV drug users- black tar heroin
what does the botulism toxin do to the body?
cleaves presynaptic proteins involved in vesicle formation and blocks vesicle docking with presynaptic membrane so there is no release of ACh
rapid onset weakness without sensory loss
what is LEMS?
antibodies to presynaptic Ca2+ channels
what condition is LEMS associated with?
small cell carcinoma
management of LEMS
3-4 diaminopyridine (blocks K+ channels)
what is myasthenia gravis?
AI antibodies to AChR leading to reduced functioning receptors causing muscle weakness and fatiguability
most patients have thymus involvement
two peaks of incidence in myasthenia gravis?
women in 30s
men 60-70s
presentation of myasthenia gravis
weakness worse throughout the day commonly in extraocular, facial and bulbar muscles (drooping eyelids, diplopia, struggle chew/ speak at the end of the day)
proximal limb weakness
SOB
diagnosis of myasthenia gravis
antibodies to ACh-R and MuSK
edrophonium test= neostigmine given which blocks breakdown and reverses weakness (trial of therapy)
management of myasthenia gravis
acetylcholinesterase inhibitors e.g. pyridostigmine
IV immunoglobulin or plasma exchange in emergency (CRISIS)
thymectomy
steroids and steroid-sparing agents
immune-mediated muscle diseases
- polymyositis
2. dermatomyositis
presentation of polymyositis
over 40 presenting with symmetrical, progressive proximal weakness developing over weeks- months
diagnosis of polymyositis
high CK
management of polymyositis
responds to steroids
presentation of dermatomyositis
symmetrical proximal muscle weakness with skin lesions (heliotrope on face)
50% have underlying malignancy
example of degenerative muscle disease
inclusion body myositis
presentation of inclusion body myositis
slow progressive weakness in 60s with characteristic thumb sparing
management of inclusion body myositis
poor response to steroids
examples of muscular dystrophies
myotonic dystrophy
Duchenne’s
Becker’s
what is myotonic dystrophy?
AD multisystem disorder with trinucleotide repeat
presentation of myotonic dystrophy
weakness frontal balding cataracts ptosis onset in 30s positive FH
presentation of Duchenne’s
woody texture muscle swelling (calves)
toe walker
positive Gower’s sign
presentation of Becker’s
woody texture calves
proximal limb wasting
risk in use of steroids to do with muscles
necrotising myopathy with risk of rhabdomyolysis
what is rhabdomyolysis?
dissolution of the muscle with leakage of toxic intracellular contents into plasma
causes of rhabdomyolysis
crush injuries
toxins
post-convulsions extreme exercise e.g. post-marathon
presentation of rhabdomyolysis
triad of myalgia, muscle weakness and myoglobinuria leading to DIC and renal failure
