Muscular & neuromuscular treatments Flashcards
Myopathy acquired causes
- autoimmune
- toxic: corticosteroids , statins , chloroquine , colchicines, alcohol
- Viral - HIV , HCV
- metabolic - Ca, K +?-
- Critical illness myopathy - immobilization
- endocrine - thryoid, parathyroid, addison’s , cushing’s
What is dermatomyositis and how does it present
Cause of inflammatory myopathy , autoimmune
- Gottron papules ( red patches on knuckles ) , periorbital odema , heliotrope rash , V sign , shawl sign , mechanic’s hands
- Acute or subacture proximal weakness, myalgia
- CK 10-50x the normal ( high )
- Anti-Mi2, Anti-MDA5, Anti0TIF-Ia , etc.
- associated with malignancies ( 10-20%) : lung , breast , ovarian , lymphoma
- muscle biopsy : perifasicular atrophy
Treatment for Dermatomyositis
- Steroids
- long term immunosuppressants parallel with steroid : methotrexate, azathioprine, mycophenolate mofetil
- If not effective : IVIG , ciclosporin
- 3rd line : rituximab , cyclophosphamide
Common NMJ disorders
1- Lambert eaton myasthenic syndrome
2- organophosphate poisoning
3- Botulinum toxin
4- congential myasthenic syndromes
What antibodies might be seen with myasthenia Gravis
Anti muscle specific kinase ( MuSK )
What is MG ( explain physiologically what happens )
AChR antibodies bind to and block receptor leading to degradation and endocytosis of AChRs and degeneration of motor end-plate and loss of postsynaptic folds.
Leads to reduced muscle membrane depolarization and increase in threshold required to initiate muscle action potential
MG presention
1- Fatiguability
2- diurnal variation
3- weakness of extra-ocular muscles: ptosis and ophthalmoplegia
4- weakness of neck extension/flexion : head drop
5- proximal limb weakness and finger extensor weakness
6- rare wasting
7- preserved reflexes
8- sensory normal
MG investigations
- AChR antibody , MuSK antibody
- Ice pack test : Ptosis will resolve after ice
- Tensilon test : endrophonium IV to assess objective improvement in muscle strength
- Neurophysiology
- Exclude thymoma ( CT chest )
MG neurophysiology
RNS
- decrement of > 10% over 5 responses = MG
- can be normal in ocular MG
- unreliable if limb is cold or patient on acetylcholinesterase inhibitors
Single fibre EMG ( SFEMG)
- increased variability in interval b/w paired action potentials of 2 muscle fibres in a single motor unit - jitter = evidence of defect in neuromuscular transmission
- jitter could be found in myopathy or denervation
MG management
1- Pyridostigmine ( plus propantheline ) : acetylcholinesterase inhibitor
- inhibits Ch breakdown by acetylcholinesterase in synaptic cleft
2- steroids
3- steroid-sparing agents : azathioprine , ciclosporin , methotrexate, mycophenolate mofetil
4- IVIg, PLEX
5- Rituximab
MG exacerbating factors
- Infection
- stress , trauma , post-op
- cholinesterase inhibitors withdrawal
- rapid introduction or increase of steroids
- electrolyte imbalance
- anaemia
drugs
Myasthenic crisis presentation and management
Neurological emergency
On onset :
- increase muscle weakness and diplopia
- respiratory failure
- O2 saturation and blood gases could be normal until late in crisis
- FVC : less than 1L = requires ICU support
Management :
- IVIg , plasma exchange , ventilation , NBM 7 NG feeding
Most common causes of polyneuropathies
- Diabetes, vitamin deficiency ( BT12 ) , endocrine , toxins, hereditary , infectious , inflammatory
What is Guillain Barre Syndrome
Acute inflammatory demyelinating polyradiculoneuropathy ( AIDP )
- acute infectious triggers
- proximal weakness but all other signs of neuropathy
Guillain Barre Syndrome presentation
Progressive weakness : hrs to days
- Areflexia
- peak of symptoms in less than 4 weeks from onset
- symmetrical
- predominantly affects motor more than sensory ( might first start with tingling and then weakness )
- autonomic dysfunction : BP, cardiac arrhythmia
- facial involvement and bulbar involvement
