Neuromuscular Disorders

Question 1

how do lower motor neurone disorders present?

Answer 1

weak, flaccid and wasted muscles
low tone
fasciculations
reduced/absent reflexes

Question 2

what is the role of the neuromuscular junction?

Answer 2

makes the muscle contract by providing the connection between the motor neurone and the muscle

Question 3

where do the motor neurones that innervate skeletal muscle fibres arise?

Answer 3

in the ventral horn of the spinal cord

Question 4

what are motor end plates?

Answer 4

the synapses formed between motor neurons and muscles

Question 5

how many motor neurons does each muscle cell respond to?

Answer 5

only one

however, a single motor neurone can control many muscle cells

Question 6

what enzyme breaks down acetylcholine and what are the products?

Answer 6

acetylcholinesterase

acetate and choline

choline is sequestered into presynaptic vesicles

Question 7

name two presynaptic disorders of the neuromuscular junction

Answer 7

botulism

lambert eaton myasthenic syndrome (LEMS)

Question 8

what causes botulism?

Answer 8

clostridium botulinum

Question 9

what is the pathophysiology of botulism?

Answer 9

botulinum toxin cleaves presynaptic proteins involved in vesicle formation, blockiung the vesicle from docking with the presynaptic membrane

this prevents muscle contraction

Question 10

how does botulism present?

Answer 10

rapid onset weakness without sensory loss

ascending paralysis

Question 11

what is the treatment for botulism?

Answer 11

supportive care

Question 12

how long does botulism last?

Answer 12

around 12 weeks

Question 13

what is the pathophysiology behind LEMS?

Answer 13

antibodies to presynaptic calcium channels lead to less vesicle release = reduced muscle contraction

Question 14

what condition does LEMS have a strong association with?

Answer 14

underlying small cell lung carcinoma

Question 15

how is LEMS managed?

Answer 15

3-4 diaminopyridine

Question 16

name a postsynaptic disorder of the neuromuscular junction

Answer 16

myasthenia gravis

Question 17

what is the pathophysiology behind myasthenia gravis?

Answer 17

autoimmune condition where antibodies to acetylcholine receptors (AChR) are produced

this reduces the number of functioning receptors causing muscle weakness and fatigue

Question 18

what condition is myasthenia gravis associated with?

Answer 18

thymic hyperplasia/thymoma

Question 19

when do symptoms start in myasthenia gravis?

Answer 19

when AChR levels reduced to 30% of normal

Question 20

when are the two peaks of incidence of myasthenia gravis?

Answer 20

females in 20’s

males in 50’s-60’s

Question 21

what is the most common initial presentation of myasthenia gravis?

Answer 21

extraocular weakness
facial weakness
bulba weakness

then becomes generalised

Question 22

how does myasthenia gravis present?

Answer 22

fatigable weakness of skeletal muscle

Question 23

what is ocular myasthenia gravis?

Answer 23

when weakness remains only in the extraocular muscles

Question 24

what parts of the limbs are usually involved in myasthenia gravis?

Answer 24

proximal parts become weak

Question 25

how is myasthenia gravis diagnsoed?

Answer 25

serum AChR antibodies single fibre EMG CT chest to look for a thymoma

Question 26

what three things are included in the acute treatment of myasthenia gravis?

Answer 26

acetylcholinesterase inhibitor IV Ig or plasma exchange thymectomy if needed

Question 27

name an acetylcholinesterase inhibitor that can be given for myasthenia gravis

Answer 27

pyridostigmine this improves muscle strength

Question 28

what emergency treatments can be given for myasthenia gravis?

Answer 28

IV immunoglobulin | plasma exchange

Question 29

what drugs can be given for long term myasthenia gravis management?

Answer 29

immunomodulating drugs | steroids

Question 30

what should be given alongside steroids in myasthenia gravis?

Answer 30

steroid sparing agents such as azathioprine or mycophenolate

Question 31

what antibiotic should be avoided in patients with myasthenia gravis?

Answer 31

gentamicin

Question 32

what is the smallest contractile unit of skeletal muscle?

Answer 32

the muscle fibre

Question 33

what is each skeletal muscle fibre surrounded by?

Answer 33

endomysium

Question 34

what is a fascicle and what encapsulates this?

Answer 34

20-80 smooth muscle fibres encapsulated by perimysium

Question 35

what forms an individual skeletal muscle?

Answer 35

many smooth muscle fascicles surrounded by epimysium

Question 36

name six possible signs and symptoms of muscle disease

Answer 36

``` myalgia weakness wasting hyporeflexia fasciculations myotonia ```

Question 37

what are fasciculations?

Answer 37

visible, fast, fine and spontaneous twitches usually a sign of disease in the motor neuron, not the muscle

Question 38

what is myotonia?

Answer 38

failure of muscle relaxation after use

Question 39

when can fasciculations occur in normal muscles?

Answer 39

precipitated by stress, caffeine and fatigue

Question 40

what blood test is often done if muscle disease is suspected?

Answer 40

CK elevated in many muscle disorders

Question 41

what is the characteristic feature of dermatomyositis?

Answer 41

heliotrope rash

Question 42

what underlying condition do many patients with dermatomyositis have?

Answer 42

malignancy

Question 43

how does polymyositis present?

Answer 43

symmetrical, progressive proximal weakness developing over weeks - months raised CK

Question 44

what drug does polymyositis respond to?

Answer 44

steroids

Question 45

what is the most common type of muscular dystrophy?

Answer 45

myotonic dystrophy

Question 46

what is the inheritance pattern of myotonic dystrophy?

Answer 46

autosomal dominant

Question 47

how does myotonic dystrophy present?

Answer 47

``` myotonia weakness cataracts ptosis frontal balding cardiac defects ```

Question 48

how does inclusion body myositis usually present?

Answer 48

slowly progressive weakness in the sixth decade of life with characteristic thumb sparing