NMJ and muscle conditions

Question 1

What is a myopathy?

Answer 1

Muscle pathology -> weakness

Question 2

Describe the presentation of Duchenne’s muscular dystrophy

Answer 2

• Presents in early childhood with problems walking, fatigue, etc
• Progressively worsening weakness
• Pseudohypertrophy of the calves
• Family Hx

Question 3

Which tests can differentiate myopathy from motor neuropathy?

Answer 3

• CK (and other enzymes) raised in myopathy eg. Duchenne’s, myositis
• EMG
• NCS

Question 4

Describe the presentation of inflammatory myositis

Answer 4

• Chronic progressive symmetrical proximal muscle weakness
• Usually painless
• May have derm involvement: shawl sign, Gottron’s papules, heliotrope rash, mechanic’s hands
• Systemic symptoms: SOB, palpitations, athralgia, weight loss

Question 5

What are the types of myositis?

Answer 5

Polymyositis: muscle only
Dermatomyositis: muscle and skin
Inclusion body myositis: distal muscles earlier

Question 6

Describe the diagnostic process for suspected myositis

Answer 6

• History and examination suggestive eg. chronic progressive prox. muscle weakness
• Bloods: general screen FBC, U+Es, LFTs, TFTs, cortisol, B12, ESR, CRP, HIV, CK, LDH, ANAs
• EMG
• MRI
• Muscle biopsy to confirm diagnosis

Question 7

Name some causes of myopathy

Answer 7

Infection/inflammation: inflammatory myositis, HIV
Autoimmune: scleroderma, etc.
Metabolic: hypothyroidism, Cushing’s, hypercalcaemia
Congenital: dystrophies

Question 8

Explain the pathophysiology of MG

Answer 8

Antibodies to the AChR -> blocks the depolarisation of the myocyte in the NMJ
-> weakness with fatiguability

Question 9

Describe the presentation of MG

Answer 9

-Extraocular muscles -> diplopia, bilateral ptosis
-Bulbar muscles -> dysphagia, quiet speech
-Facial muscles -> ‘myasthenic snarl’
-Neck muscles -> head droop
-Limbs -> proximal muscle weakness
Symptoms are worse towards the end of the day, worsening with repetition
Progressively worsening

Question 10

Describe the epidemiology of MG

Answer 10

<50s F and assoc w autoimmune disease eg. RA

>50s M and assoc w thymic tumour

Question 11

Describe the diagnostic process in suspected MG

Answer 11

• History and examination suggestive eg. progressively worsening muscle weakness w fatiguability
• Bloods: general screen for metabolic causes of myopathy, antibodies (anti-AChR)
• EMG
• Tensilon test (edrophonium IV)

Question 12

Describe the management of MG

Answer 12

Chronic:

• Mild: cholinesterase inhibitor eg. pyridostigmine. +/-Steroids
• Moderate: pyridostigmine, steroids, immunosuppressants, etc.
• Biologics
• Thymectomy if thymoma present, severe disease, or + AChR antibodies

Question 13

Describe the management of myasthenic crisis

Answer 13

A to E approach

• Stabilise airway, consider need for I+V, ICU
• IVIG or plasma exchange
• Start high dose steroids

Question 14

List the side effects of anti-cholinesterase drugs

Answer 14

SLUDGE

• Salivation
• Lacrimation
• Urination
• Diarrhoea
• GI cramps
• Emesis

Question 15

Describe the pathophysiology of LEMS

Answer 15

Antibody to voltage gated calcium channels on the pre-synaptic membrane -> decreased release of ACh into synaptic cleft of NMJ
-Assoc w SCLC

Question 16

Describe the presentation of LEMS

Answer 16

• Progressive muscle weakness. Often limbs > eyes

- Worse in the morning, improves with use

Question 17

Describe the diagnosis of LEMS

Answer 17

• History and examination suggestive
• Bloods: VGCC, anti-AChR antibodies, etc
• Imaging: CXR, HRCT
• Edrophonium test: only small improvement vs MG

Question 18

Describe the presentation of neurofibromatosis

Answer 18

2 types:
1- presents in teens/young adults. Characterised by Cafe au Lait spots, Lisch nodules, neurofibromas. Multiple organ system involvement - LDs, gliomas, renal, etc.
2- Cafe au Lait spots, bilateral acoustic neuromas, cataracts