Nerve and muscle disease Flashcards
What are the three types of muscle?
Skeletal, smooth, cardiac
Describe skeletal muscle
Highly organised
There is an endomysium, perimysium and epimysium
What is a fascicle encapsulated by?
Perimysium
What are a large group of fascicles encased in?
Epimysium
What is the smallest contractile unit surrounded by?
Endomysium
Describe smooth muscle
Cells not striated Single central network Significant connective tissue around them No sarcomeres Actin:Myosin ratio 10:1
What are the three types of smooth muscle fibres?
Type I
Type IIa
Type IIb
Describe type 1 fibres
Slow oxidative- dense capillary network, myoglobin, resist fatigue
Describe type IIa fibres?
Fast oxidative- aerobic metabolism
Describe type IIb fibres?
Fast glycolytic, easily fatigued
What is myotonia?
Failure of muscle relaxation after use
What are fasciculations?
Visible, fast, fine, spontaneous twitch
Fasciculations only appear if muscle has pathology TRUE/FALSE
May occur in healthy muscle-triggers include stress, caffeine and fatigue
Usually a sign of disease in motor neurone
What myopathy can statins cause?
Autoimmune myositis (always check CK)
What 5 drugs can cause myopathies?
Statins Hydroxycloroquine Amiodarone Diuretics A-interferon
What is the MRC muscle power grading?
0-No movement at all
1-Flicker of movement when attempting to contract muscle
2-Some muscle movement if gravity removed but none against gravity
3- Movement against gravity but not against resistance
4- Movement against resistance but not full strength
5-Normal strength
Name a postsynaptic disorder
Myasthenia gravis
Name 2 presynaptic disorder
Botulism-Clostridium botulinum
Lambert Eaton Myasthenic Syndrome (LEMS)
What are the synapses formed between motor neurones and muscle called?
Motor end plates
Where do the cell bodies that innervate the motor neurones that innervate the skeletal muscle fibres arise?
Ventral horn of the spinal cord
TRUE/FALSE
A single motor neuron may control many muscles but each muscle cell responds only to one motor neuron
TRUE
What is curare?
Muscle relaxant used in anaesthetics that competes with acetylcholine and blocks transmission of information
What is McArdle’s disease?
AR, usually presents in 1st decade of life
caused by myophosphorylase deficiency
Muscle pain soon after starting exercise
Second wind phenomenon
Why should patients with McArdles disease stop if they get severe pain when exercising?
As it may increase risk of rhabdomyolysis with myoglobinuria and subsequent AKI
Name the chronic autoimmune disease affecting post-synaptic nicotinic acetylcholine receptors at NMJ
Myasthenia gravis
What is the most common disorder of the NMJ?
Myasthenia gravis
What is the typical Myasthenia gravis patient?
F>M (ratio 3:2)
Females in 3rd decade
Males in 6/7th decade
When do the symptoms of myasthenia gravis start?
When the number of Ach receptors decreases to 30% of normal
Clinical features of myasthenia gravis
Muscle fatiguability/weakness
Occular features commonly appear first
Proximal muscle weakness more marked than distal muscles
Jaw, facial muscles, speech and/or swallow and resp muscles are also affected
weakness on neck flexion
Name two complications of myasthenia gravis
Myasthenia crisis
Cholinergic crisis
What is myasthenia crisis?
Weakness of muscles of respiration cause ventilator failure
How do you monitor for myasthenia crisis?
Measure vital capacity and tidal volume
If vital capacity falls below 15mL/kg then urgent elective tracheal intubation and ventilation considered
What is the treatment for myasthenia crisis?
Plasmapheresis
IV immunoglobulins
Systemic steroids
What are the symptoms of cholinergic crisis?
Sweating
Hypersalivation
Bronchial hyper secretions and miosis
Name 4 common associations with myasthenia gravis
Thymic hyperplasia
Thymoma
Hyperthyroidism
SLE
What is the drug to look out for which can exacerbate myasthenia?
Gentamicin
What testing is done for myasthenia gravis?
Anti-AchR
If this is negative can check for anti-MuSK
what are the three investigations for those you suspect to have myasthenia gravis?
Antibody testing (anti-AchR and anti-MuSK) Repetitive nerve stimulation tests Thyroid function test and CT thymus
What is symptomatic control of acetylcholinesterase inhibition with?
Pyridostigmine
What immunosuppressive agents are used to improve myasthenic weakness and establish remission
Corticosteroids
Azathioprine
In myasthenia gravis what is morbidity due to?
Resp failure and aspiration pneumonia
Describe muscular dystrophy
Inherited, non inflammatory, progressive, no central or peripheral abnormality
What is the commonest muscular dystrophy in adults?
Myotonic dystrophy
What is myotonic dystrophy and how is it inherited?
Multisystem progressive disease
AD: tri-nucleoide repeat on Ch 19 (with anticipation)
What are the clinical features of myotonic dystrophy?
Sternocleidomastoid & distal limb muscle affected first Facial weakness ptosis, ophthalmoplegia Christmas tree like cataracts Hollowing of temples Early frontal balding
What is Lambert-Eaton Myasthenic syndrome (LEMS)?
NMJ disorder caused by impaired release of acetylcholine by pre-synaptic terminal due to autoimmune antibodies
What has LEMS got a strong association with?
Underlying small cell carcinoma
What are the clinical features of LEMS?
Insidious onset of weakness of proximal muscles (lower extremity mainly affected) Autonomic features (constipation, postural hypotension, impotence and dry mouth) Deep tendon reflexes diminished/abscent
What is diagnosis of LEMS established by?
Presence of anti-VGCC antibodies
Characteristic electrophysiological findings using a 20-50Hz repetitive stimulation
CT scan (to rule out malignancy)
What is the treatment for LEMS?
3,4-diaminopyridine (amifampridine)
What is Charcot-Marie-Tooth disease?
A group of hereditary neuropathies
Can be inherited or AD (most common), AR or X-linked
Onset in first 2 decades with motor symptoms In lower limbs
Sensory loss follows same pattern as muscle weakness
Inverted champagne bottle appearance
What does Charcot Marie Tooth disease look like histopathologically?
Schwann cells proliferate and form concentric arrays of demyelination around the demyelinated axon - onion bulb appearance
What is Guillian Barre syndrome?
Acute neuromuscular weakness causing demyelination and axonal injury
With GBS what infections do most patients have a preceding history of?
Campylobacter
How does GBS present?
Symmetrical, progressive ascending sensorimotor paralysis
Usually stops progressing 4wks from its onset
How is GBS diagnosed?
Usually clinical
However
LP (show high CSF protein) and nerve conduction studies (suggestive of patchy proximal and distal demyelination ) sometimes helpful
What is the management of GBS?
Plasma exchange or IV immunoglobulins
What is chronic inflammatory demyelinating polyradiculoneuropathy (CIPD)
Acquired demyelinating peripheral nervous system disease characterised by progressive or relapsing proximal and distal weakness with hyporeflexia/areflexia and a distal sensory loss (paraesthesia and numbness)
How is CIDP diagnosed?
CliniCAL
Supported by electrophysial nerve conduction studies & CSF analysis (high protein)
What is the treatment for CIPD?
Oral steroids or IV immunoglobulins
What is Spinal muscular atrophy?
AR neuromuscular disorder
Congenital degeneration of anterior horns of spinal cord (LMN lesions) which leads to progressive muscular wasting often leading to early death
What does the severe form of spinal muscular atrophy manifest itself as in early life?
Floppy baby syndrome
What is poliomyelitis?
Symmetrical progressive proximal weakness developing over weeks to months
What is poliomyelitis caused by?
Poliovirus (faecal-oral transmission
The infection causes destruction of cells in the anterior horn of spinal cord (LMN death)
What is dermatomyositis similar to?
Clinically similar to poliomyelitis but ass with skin lesions, “heliotrope” rash on face
up to 50% have underlying malignancy
How does inclusion body myositis present?
Typically slowly progressive weakness in 6th decade of life with characteristic thumb sparing
What is rhabdomyolysis?
Dissolution of muscle
Damage to skeletal muscle causes leakage go large quantities of toxic intracellular contents into plasma
How does rhabdomyolitis present?
Triad
Myalgia
Muscle weakness
Myoglobinuria
What can be complications of Rhabdomyolysis?
Acute renal failure
DIC
What is botulism- clostridium botulinum from?
Organism present in soil
Food and wounds can become infected
ALSO IV drug users-black tar heroin
How does botulism-clostridium botulinum present?
Rapid onset weakness without sensory loss
How does botulism-clostridium botulinum work its magic?
It cleaves presynaptic proteins involved in vesicle formation and blocks vesicle docking with the presynaptic membrane
