Flashcards in Muscle and neuromuscular junction disease Deck (11):
What are 2 pre-synaptic muscle disorders?
Lambert-eaton myaesthenic syndrome
what is botulism?
-what is this cause by?
-what is the pathophysiolofy
Clostridium botulinum. Found in soil. Food and woulds can become infected. Intravenous drug users – black tar heroin.
Botulinum toxin cleave presynaptic proteins involved in vesicle formation and block vesicle docking with the presynaptic membrane. Rapid onset weakness without sensory loss. Some medical (and cosmetic) uses of toxin
What is Lambert eaton myaesthenic syndrome? what is this strongly associated with?
Lambert Eaton Myasthenic Syndrome -antibodies to presynaptic calcium channels leads to less vesicle release. Strong association with underlying small cell carcinoma.
Presynaptic problem that is the sequelae to cancer
What is myaesthenia gravis?
Postsynaptic autoimmune disorder:
-antibodies to acetyl choline receptors (AchR)
-reduced no. of functioning receptors leads to muscle weakness and fatiguability
What is the pathophysiology of myaesthenia gravis?
-reduced number of ACh receptors and flattening of endplate folds
-even with normal amounts of ACh transmission becomes inefficient
-symptoms start when ACh receptors reduced to 30% of normal
-as the Ach receptors are blocked they die and grow back, but less and less do grow back
-ACh antibodies are found in 80 - 90% patients
-Antibodies block binding of ACh but also trigger inflammatory cascades that damage the folds of the postsynaptic membrane
Thymus plays a role, 75% patients have hyperplasia or thymoma
At what age does myaesthenia gravis affect people?
May occur at any age but two peaks of incidence
females in 3rd decade
males in 6th or 7th decade
female:male ratio - 3:2
describe the clinical features of myaesthenia gravis
Weakness typically fluctuating - worse through the day
Most common presentation with extraocular weakness, facial and bulbar weakness
Weakness fluctuates and repetitive motions are hardest e.g. speaking/swallowing
Limb weakness typically proximal
Ptosis – extraocular weakness most common
Bilateral facial weakness
What is the treatment of myaesthenia gravis?
acetylcholinesterase inhibitor – pyridostigmine
increase concentration of Ach in cleft initiallyy
ultimately autoimmune so use immunosupression
steroids / azathioprine
emergency treatment with plasma exchange or immunoglobulin
What is the typical history for inclusion body myositis?
Historically thought to be inflammatory but little response to steroid
Typically slowly progressive weakness in 6th decade of life with characteristic thumb sparing
What is myotonic dystrophy?
-what are the clinical features?
Commonest muscular dystrophy
Myotonia, weakness, cataracts, ptosis, frontal balding, cardiac defects
Trinucleotide repeat disorder with anticipation