NMJ, Muscle: MG, LES, DMD/BMD, MD, GBS, MND

Question 1

MG
-epidemiology
-pathophysiology
-presentation

Answer 1

Not common
-young women, older men

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

Question 2

MG
-investigations, diagnosis

Answer 2

Blood
-AChR - negative does not rule out possibility
-MuSK AB
-high association with other AI (T1DM, thyroiditis)

Imaging
-thymus hyperplasia - overactivity
-thymoma => rarely malignant but removed eventually

Diagnostic - rep EMG stimulation
-decreased amplitude over time

Question 3

MG
-management

Answer 3

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, metho)

Crisis - breathing and swallowing problems => ICU resp support, plasmapheresis, IVIG

Question 4

LES
-pathophysiology
-presentation

Answer 4

AI AB against presynaptic VGCC in PNS

Repeated muscle contractions => increased muscle strength
-limb girdle weakness (mainly in legs)
Autonomic involvement - urination/defecation issues, impotence
Hyporeflexia

Eye symptoms not a feature

Question 5

LES
-investigations

Answer 5

EMG => incremental response to repetitive electrical stimulation

Autoantibody electrical stimulation

Chest CT - small cell lung cancer association

Question 6

LES
-management

Answer 6

SCLL management

AChinh or aminopyridines (block K channels => increases Ca influx) - diaminopyridine/pyridostigmine
Severe - CS +DMARD (pred + aza)

Plasmapheresis
IVIG

Question 7

Polymyositis and dermatomyositis
-pathophysiology, presentation
-epidemiology

Answer 7

Inflammatory => symmetrical proximal muscle weakness
-tender
-resp muscle weakness, IDL
-dysphagia, dysphonia
-Raynauds

P - no skin signs
D - heliotrope rash on cheeks, eyelids
-photosensitivity
-red papules over finger extensors
-dry, scaly, cracked hands on palmar
-nailfold capillaries

Middle age females

Question 8

Polymyositis, dermatomyositis
-investigations
-management

Answer 8

High CK
-other muscle enzymes high (LDH, aldolase, AST, ALT)
AB - more specific
P - anti Jo
D - anti Mi

EMG

Definitive - muscle biopsy

Definitive - pred
Supportive - sun protection, exercise

Question 9

DMD and BMD
-pathophysiology
-presentation

Answer 9

X recessive - mutated dystrophin gene
-needed to connect muscle membrane to actin

DMD - frameshift => severe
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
-10y/o+
-intellectual impairment less common

Question 10

DMD and BMD
-investigations
-management

Answer 10

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

Question 11

Myotonic dystrophy
-epidemiology, pathophysiology
-presentation

Answer 11

Inherited AD myopathy - 20-30 y/o
Affects skeletal, cardiac, smooth muscle

Myotonic dystrophy - contracted muscle destruction
-frontal balding
-arrythmias
-early cataracts
-DM

DM1 - distal weakness
DM2 - proximal weakness

Question 12

Myotonic dystrophy
-investigations
-management

Answer 12

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

Question 13

GBS
-presentation
-pathophysiology

Answer 13

Adults, males
Immune mediated attack on Schwann cells in PNS
-often triggered by infection - 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

Question 14

GBS
-investigations, diagnosis
-management

Answer 14

Definitive
-nerve conduction - demyelination => slow conduction
-lumbar puncture - normal WCC, high protein

ABG - resp acidosis
Spirometer - restrictive (muscle weakness)
-May require ventilation

IVIG - stop harmful AB from causing further damage
Plasmapheresis
Resp failure support

Complete recovery in 1 year
-long term rehab needed

Question 15

GBS differentials
-timeframe and management

Answer 15

Chronic inflammatory demyelinating polyneuropathy
-AB mediated inflammation => demyelination of peripheries
-insidious onset over months
-treated with IC

Question 16

Investigations used for suspected muscle conditions

Answer 16

EMG neurophysiology - good to rule out other neuropathies

Muscle biopsy analysis - immunohistology, staining

MRI muscle

DNA analysis - gold standard for direct mutation detection

Question 17

MND
-presentation
-investigations
-management

Answer 17

60-70s males

LMN and UMN
-fasciculations
-wasting of intrinsic hand muscles, tibialis anterior (foot drop, high steppage gait)
-eye sparing
-no cerebellar, sensory signs

Clinical diagnosis
EMG - reduced action potentials with increased amplitude

Riluzole
Respiratory care
-NIV BIPAP used at night