Disorders of the neuromuscular junction and muscle Flashcards
What are motor end plates?
Synapses which form between motor neurones and the muscle
Describe the locations of endomysium, perimysium and epimysium
Endomysium surrounds muscle fibres
Perimysium surrounds fascicles
Epimysium surrounds individual muscles
Describe the different muscle fibre types
Type I - slow oxidative, faitgue resistant
Type IIa - fast oxidative, aerobic metabolism
Type IIb - fast glycolytic, easily fatigues
Give examples of presynaptic disorders
Botulism
Lambert eaton myasthenic syndrome (LEMS)
Which organism causes botulism and where is it found?
Clostridium botulinum
Organism present in soil which can infect food and wounds
IVDU can become infected if their drugs are not clean
How does botulism present?
Neuromuscular and respiratory weakness
What is lambert eaton myasthenia syndrome?
A paraneoplastic syndrome with antibodies to presynaptic calcium channels
How does lambert eaton myasthenia syndrome present?
Affects large muscles - patient struggles to get up
Symptoms improve with exercise
Lambert eaton myasthenia syndrome is strongly associated with which condition?
Small cell carcinoma
How is lambert eaton myasthenia syndrome treated?
3-4 diaminopyridine
Give an example of a postsynaptic disorder
Myaesthenia Gravis
Which antibodies are involved in myasthenia gravis?
Anti AChR
Anti Musk
What is the most common disorder of the neuromuscular junction?
Myasthenia Gravis
Who gets myasthenia graves?
More common in females
Presents in females in the 3rd decade
Presents in males in the 6th or 7th decade
What is the pathophysiology behind myasthenia gravis?
Reduced numbers of functioning (ACh) receptors leads to muscle weakness and fatigueabillity
Flattening of endplate folds
75% of patients also have hyperplasia of the thymus
Describe the clinical presentation of myasthenia gravis
Fluctuating weakness
Diplopia and bilateral ptosis (EO muscle weakness)
Tired chewing meals (facial and bulbar muscle weakness)
Proximal limb weakness
Respiratory muscle weakness (late presentation)
How can myasthenia graves be treated acutely and chronically?
ACUTE TREATMENT
Acetylcholinesterase inhibitors
IV immunoglobulin
Thymectomy
CHRONIC TREATMENT
High dose steroids and steroid sparing agents
Plasma exchange or immunoglobulin
Which medication needs to be avoided in patients with myasthenia gravis due to the risk of myasthenia crisis?
Gentamicin
What are fasciculations and what causes them?
Fast spontaneous twitches in muscle
May occur in healthy muscle and be precipitated by stress, caffeine and fatigue
May occur in denervated muscle which has become hyper excitable
What is myotonia?
Failure of muscle relaxation after use
What is myalgia?
Muscle weakness, wasting and hyporeflexia
What causes rhabdomyolysis?
Extreme exercise
Falls
Crush injuries
Acute renal failure and DIC
What is rhabdomyolysis?
Damage to skeletal muscle causes leakage of toxic intracellular contents into plasma
What triad of symptoms does rhabdomyolysis present with?
Myalgia, muscle weakness and myoglobinuria
Give examples of immune mediated muscle disorders
Polymyositis
Dermatomyositis
Describe polymyositis
Symmetrical proximal muscle weakness develops over weeks to months
Raised CK
Responds to steroids
Describe dermatomyositis
Clinically similar to polymyositis but with skin lesions
Helioptrope rash on the face
Big association with underlying malignancy
What is inclusion body myositis?
A degeneratie muscle disorder
Slowly progressive weakness
Characteristic sparing of the thumb
Occurs age >60
Give examples of inherited muscular disorder
Duchenne and Beker muscular dystrophies
Myotonic dystrophy
Describe the genetics of myotonic dystrophy
Most common of the muscular dystrophies
Autosomal dominant inherited disorder
Trinucleotide disorder with anticipation
Describe how myotonic dystrophy presents
Multisytem
Weakness
Cataracts and ptosis
Frontal balding
Cardiac defects
What drugs can cause myopathy?
Corticosteroids
Statins
Amiodarone
Diuretics
Oral contraceptive
