NMJ, Muscle Pathologies - Myasthenia Gravis, Lambert Eaton Syndrome, Polymyositis, Dermatomyositis, DMD, BMD, GBS ☺️ Flashcards
MG
Epidemiology
Pathophysiology
Presentation
Not common
- young women, older men
- less common in childhood
AI - ACh rec AB => muscle contraction reduced
Gradual/rapid onset after illness, stress, pregnancy
Fatiguable, painless muscle weakness that improves with rest
- eyes, eyelid, facial, speech muscles
- limbs, resp muscles
No impact on GU, heart
MG
Investigations
Blood
- AChR - negative does not rule it out
- MuSK AB
- high association with other AI (T1DM, thyroiditis)
Imaging
- thymic hyperplasia - overactivity
- thymoma => rarely malignant but removed eventually
Diagnostic - rep EMG stimulation
-decreased amplitude over time
MG
Management
Lifestyle - avoid triggers
- sufficient rest, stress reduction
- flu/pneumonia jab
Symptomatic - pyridostigmine (AChesterase inh)
Immune system control - CS (induce remission, taper down eventually)
2nd line - DMARD (aza, methotrexate etc)
Crisis - breathing and swallowing problems => ICU resp suppoort, plasmaphresis, IVIG
LES
Pathophysiology
Presentation
AI AB against presynaptic VGCC in peripheral nervous system
Repeated muscle contractions => increased muscle strength
-limb girdle weakness (mainly in legs)
Autonomic involvement - urination/defecation issues, impotence
Hyporeflexia
Eye symptoms not a feature
LES
Investigations
EMG => incremental response to repetitive electrical stimulation
Autoantibody serology
Chest CT - small cell lung cancer association
LES
Management
Manage small cell lung cancer
AChinh or aminopyridines (blocks K channels => increase Ca influx)
Severe - CS + DMARD
-eg pred + azathio
Plasmapheresis
IVIG
Polymyositis and dermatomyositis
- pathophysiology and presentation
- epidemiology
Inflammatory => symmetrical proximal muscle weakness
- can be tender
- resp muscle weakness, IDL
- dysphagia, dysphonia
- Raynaud’s
P - no skin signs D - heliotrope rash on cheeks, eyelids -photosensitive -red papules over finger extensors -dry, scaly, cracked hands on palmar -nail fold capillaries
Middle aged females
Polymyositis and dermatomyositis
- investigations
- management
High CK -other muscle enzymes high (LDH, aldolase, AST, ALT) AB - more specific P - anti Jo D - anti Mi
EMG
Definitive - Muscle biopsy
Definitive - prednisolone
Supportive
-sun protection
-exercise
DMD and BMD
- pathophysiology
- presentation
X recessive - mutated dystrophin gene
-needed to connect muscle membrane to actin
DMD - frameshift => severe form
BMD - non frameshift => milder form
DMD
- Progressive proximal muscle weakness
- Calf pseudohypertrophy
- Gowers sign - arms needed to stand up
- Waddling gait
- Loss of walk by 12
- Intellectual impairment common
BMD
- 10 y/o+
- Intellectual impairment less common
DMD and BMD
- investigations
- management
High CK - released in muscle damage
Definitive - molecular diagnosis
1st line - CS
- improve motor and lung function
- delay loss of ambulation, cardiomyopathy
Physio, OT input
Myotonic dystrophy
- epidemiology, pathophysiology
- presentation
Inherited AD myopathy - 20-30 years old
-affected skeletal, cardiac, smooth muscle
DM1, 2
Myotonic dystrophy - contracted muscle destruction
- frontal balding
- arrythmias
- early cataracts
- DM
DM1 - distal weakness
DM2 - proximal weakness
Myotonic dystrophy
- investigations
- management
Definitive - genetics
- DM1 - CTG repeat C19
- DM2 - repeat expansion C3
No cure, focus on managing symptoms
Physio - maintain strength and endurance, control MSK pain
OT - canes, braces, walkers
Symptomatic management
- arrythmias
- cataracts
GBS
- presentation
- pathophysiology
Adults, males
Immune mediated attack on Schwann cells in PNS
-often triggered by infection
Infection trigger (campylobacter jejuni)
- leg, back pain => PROGRESSIVE ASCENDING SYMMETRICAL WEAKNESS OF ALL LIMBS
- more motor than sensory loss
- reduced reflexes
Resp muscle weakness
Urinary retention, constipation
Diplopia
Bilateral facial palsy
Dysphagia
GBS
- investigations and diagnosis
- management
Definitive
- nerve conduction - demyelination => slow conduction
- lumbar puncture - normal WCC, high protein
ABG - resp acidosis
Spirometry - restrictive (muscle weakness)
-may require ventilation
IVIG - stop harmful AB from causing further damage
Plasmapheresis
Resp failure support
Complete recovery in a year
-long term rehab needed
What could be a possible differential
- how does this differ to GBS
- timeframe and management
Chronic inflammatory demyelinating polyneuropathy
- AB mediated inflammation => demyelination of peripheries
- insidious onset over months
- treated with steroids, IS
