Peripheral Neurology

Question 1

Complete the following sentences about peripheral nerve anatomy:

1. incoming sensory information enters via ? [1]
2. motor information exits cord via ? [1]
3. collections of nerve cell bodies in PNS known as ? [1]

Answer 1

1. posterior root
2. anterior root
3. ganglia

Question 2

What are the 3 types of peripheral nerve fibres and what do each respond to? [3]

Answer 2

1. Large fibres (myelinated)
   
   • motor nerves
   • proprioception
   • vibration
   • light touch
2. Thinly myelinated fibres
   
   • light touch
   • pain
   • temperature
3. Small fibres (unmyelinated)
   
   • light touch
   • pain
   • temperature

Question 3

Describe how an action potential is propagated at the neuromuscular junction [7]

Answer 3

1. Action potential propagates through an axon to the neuromuscular junction
2. Voltage-gated Ca²⁺ channels open
3. Ca²⁺ influx causes neurotransmitter-filled vesicles to fuse with the cell membrane
4. ACh is released into the synaptic cleft and binds to receptors, causing the ion channels to open
5. ACh binds to the postsynaptic receptors and causes the influx of Na⁺, which depolarises the cell
6. Postsynaptic muscle cell depolarises, causing the opening of voltage-gated Ca²⁺ channels.
7. The influx of Ca²⁺ initiates muscle contraction

Question 4

The clinical presentation of neuropathy depends on the type and distribution of affected fibres. What clinical signs would be present if:

1. motor nerve fibres are affected? [2]
2. large myelinated sensory nerve fibres are affected? [4]
3. small (thinly myelinated/unmyelinated) nerve fibres are affected? [5]
4. autonomic nerve fibres are affected? [4]

Answer 4

1. if motor neurons affected:
   
   • weakness
   • muscle atrophy
2. if large myelinated sensory neurons affected:
   
   • sensory ataxia,
   • loss of vibration sense
   • +/- numbness and tingling
3. if small nerve fibres affected:
   
   • impaired pin prick,
   • temperature, painful burning
   • numbness and tingling
4. if autonomic neurons affected:
   
   • postural hypotension,
   • erectile dysfunction,
   • GI disturbance,
   • abnormal sweating

Question 5

Length-dependent axonal neuropathy:

1. what is it? [1]
2. who gets it? [1]
3. presentation? [5]

Answer 5

1. What is it?
   
   • Most common type of neuropathy that causes diffuse involvement of peripheral nerves
2. Who gets it?
   
   • Age > 50 years
3. Presentation?
   
   • Length dependent: starts in toes/feet
   • Symmetrical
   • Slowly progressive
   • No significant sensory ataxia
   • Any weakness is distal and mild

Question 6

What are the causes of length-dependent axonal neuropathy? [11]

Answer 6

1. Diabetes
2. Alcohol
3. Nutritional: Folate/B12/thiamine/B6 deficiency
4. Immune mediated: Rheumatoid arthritis, Lupus, vasculitis, polyarteritis nodosa
5. Metabolic/endocrine: Renal failure, hypothyroidism
6. Drugs: Isoniazid, Cisplatin, Amiodarone, Gold
7. Infectious: HIV, hepatitis B & C
8. Inherited: Charcot-Marie-Tooth, hereditary neuropathy with liability to pressure palsy (HNPP)
9. Neoplastic: Myeloma
10. Paraneoplastic
11. Critical illness

Question 7

Describe acute inflammatory demyelinating neuropathy: “Guillain-Barré syndrome”

1. Cause? [1]
2. Presentation? [3]
3. Treatment? [2]

Answer 7

1. Causes:
   
   • post-infectious autoimmune aetiology
   • (e.g. campylobacter, CMV, EBV)
2. Presentation:
   
   • progressive (ascending) weakness over days
   • flaccid, quadriparesis with areflexia
   • +/- respiratory/bulbar/autonomic involvement
3. Treatment:
   
   • IV immunoglobulin or
   • apheresis

Question 8

What is chronic inflammatory demyelinating polyneuropathy (CIDP) and how do you manage it? [3]

Answer 8

1. chronic form of Guillain-Barré syndrome
2. give steroids and IV immunoglobin

Question 9

What are the typical symptoms of muscle disease? [13]

Answer 9

1. Proximal limb weakness
   
   • difficulty raising arms above head, arising from seated position
2. Facial weakness
   
   • characteristic myopathic facies
   • drooling
3. Eyes
   
   • ptosis
   • ophthalmoplegia
4. Bulbar
   
   • dysarthria
   • dysphagia
5. Neck and spine
   
   • head drop
   • scoliosis
6. Respiratory
   
   • breathlessness (especially on lying flat)
7. Myocardial
   
   • exercise intolerance
   • palpitations

Question 10

What are the different classifications of muscle disease? [6]

Answer 10

1. Muscular dystrophies
2. Metabolic muscle disorders
3. Mitochondrial disorders
4. Myotonic dystrophies
5. Inflammatory muscle disorders
6. Neuromuscular junction disorders

Question 11

Give examples of muscular dystrophies [4]

Answer 11

1. dystrophinopathies (Duchenne/Becker)
2. fascioscapulohumeral (FSH) dystrophy
3. limb girdle dystrophy
4. oculopharyngeal dystrophy

Question 12

Give examples of metabolic muscle disorders [2]

Answer 12

1. glycogen storage diseases
2. defects of fatty acid metabolism

Question 13

Give examples of inflammatory muscle disorders [3]

Answer 13

1. polymyositis
2. dermatomyositis
3. inclusion body myositis

Question 14

Give examples of neuromuscular junction disorders [2]

Answer 14

1. Myasthenia Gravis
2. Lambert Eaton syndrome

Question 15

Describe Myasthenia Gravis under the following headings:

1. What is it? [2]
2. Associated Conditions? [3]
3. Who gets it? [2]
4. Presentation? [6]
5. Investigation [3]
6. Management [2]

Answer 15

1. What is it?
   
   • autoimmune disorder:
   • targeting antibodies to acetylcholine receptor at post-synaptic NMJ
2. Associated Conditions?
   
   • associated with other autoimmune disorders
   • may also be associated with thymic hyperplasia or thymoma
3. Who gets it?
   
   • young women in 20’s
   • older men in 70’s
4. Presentation?
   
   • Fatigable weakness of ocular, bulbar, neck, respiratory and/or limb muscles
5. Investigation
   
   • antibodies to AChR present in 85% of cases;
   • single fibre EMG and repetitive nerve stimulation also abnormal
6. Management
   
   • Pyridostigmine (anti-acetylcholine esterase)
   • Immunosuppressive therapies (e.g. steroids and intravenous immunoglobulin)