Neuropathic Pain/polyneuropathy

Question 1

What is neuropathic pain?

Answer 1

Neuropathic pain is caused by an abnormal functioning of the sensory nerves delivering abnormal and painful signals to the brain.

Question 2

What causes neuropathic pain?

Answer 2

Postherpetic neuralgia from shingles in the distribution of a dermatome and is usually on the trunk

Nerve damage from surgery

Multiple sclerosis

Diabetic neuralgia which typically affects the feet

Trigeminal neuralgia

Complex regional pain syndrome

Question 3

What are the typical features of neuropathic pain?

Answer 3

Burning
Tingling
Pins and needles
Electric shocks
Loss of sensation to touch of the affected area

Question 4

What questionnaire can be used to diagnose neuropathic pain?

Answer 4

DN4 questionare
This is used to assess the characteristics of the pain and examination of the affected area. They are then scored out of 10 for their pain. A score of 4 or more indicates neuropathic pain.

Question 5

What can be used for neuropathic pain?

Answer 5

There are four first line treatments for neuropathic pain:

Amitriptyline is a tricyclic antidepressant
Duloxetine is an SNRI antidepressant
Gabapentin is an anticonvulsant
Pregabalin is an anticonvulsant

Question 6

Even though trigeminal neuralgia is a type of neuropathic pain, what is used for trigeminal neuralgia?

Answer 6

Carbamazepine is used as first line for trigeminal neuralgia, and if this doesn’t work then refer to a specialist

Question 7

What is complex regional pain syndrome?

Answer 7

This is a condition where areas are affected by abnormal nerve functioning causing neuropathic pain and abnormal sensations. It is usually isolated to one limb. Often it is triggered by an injury to the area.

The area can become very painful and hypersensitive even to simple inputs such as wearing clothing. It can also intermittently swell, change colour, change temperature, flush with blood and have abnormal sweating.

Treatment is often guided by a pain specialist and is similar to other neuropathic pain.

Question 8

What is polyneuropathy?

Answer 8

A disorder where there is damage to multiple peripheral nerves

Question 9

What can polyneuropathy cause?

Answer 9

Either affects the axon of nerves or the myelin (demyelination/axonal loss)

Can affect lower motor neurones, somatosensory and autonomic nerves

Question 10

What are the causes of polyneuropathy?

Answer 10

The most common are: diabetes, alcohol, B12

Metabolic causes- diabetes, hypothyroidism
Toxins- alcohol, drugs (especially chemo), heavy metals
Vit deficiencies- B1,3,6,12, folate
Inflammatory- gullain barre syndrome, vasculitis, connective tissue disorders
Hereditary- charcot marie tooth disease
Neoplastic- carcinoma, lymphoma
Idiopathic

Question 11

What is the clinical presentation of polyneuropathy?

Answer 11

Sensory- distal sensory loss, poor balance, loss of dexterity, numbness in the feet, paraesthesia, neuropathic pain

Motor- remember that polyneuropathy affects the lower motor neurones, therefore there will be LMN signs- hypoteflexia, muscle weakness, wasting, fasciculation

Autonomic- innervates many different organs, so the symptoms are very varied- orthostatic hypootension, sweating dysfunction, erectile dysfunction, gastric paresis (patient will present with early satiety and bloating)

Question 12

What is the late clinical presentation of polyneuropathy?

Answer 12

Patients will present with the consequences of damage to these different nerves

• skin changes
• foot ulcers
• charcot joint

Question 13

What would the presentation of axonal degeneration be?

Answer 13

Usually chronic, develops over months- years
Sensory symptoms > motor symptoms in early disease
Produces a symmetric length dependent polyneuropathy- glove and stocking
Normally not proprioceptive however if there is early proprioceptive loss then think dorsal column pathology like vit B12 deficiency

Examples= diabetes, alcohol, vit deficiencies

Question 14

If the mechanism behind the nerve damage is demyelination how does this present and what are the causes?

Answer 14

This typically affects the motor nerves
Patients often present with weakness- which usually starts distally

Acutely it is caused by GBS, with patients having a history of GI or respiratory infection, acute paralysis reaches maximum intesity after 2 weeks of symptom onset

GBS is an emergency it can lead to respiratory failure

Chronically it is caused by chronic inflammatory demyelinating polyneuropathy, charcot marie tooth type 1

Question 15

How do charcot marie tooth patients present?

Answer 15

Inverted champagne bottle legs
Foot drop
High arch
Hammer toes

Question 16

What ix are done for polyneuropathy?

Answer 16

Initial bloods- FBC, U and Es, CRP, glucose, HbA1C, LFTs, TFTs, b12/folate, serum electrophoresis

Depending on clinical picture

• nerve conduction studies
• lumbar puncture if you are suspecting GBS (will show raised proteins)
• specific blood tests
• skin and nerve biopsy

Nerve conduction studies…
These help distinguish axonal from demyelinating
Axonal- there will be a normal conduction velocity and a reduced amplitude
Demyelinating- reduced conduction velocity, conduction block

Question 17

How do you manage polyneuropathy?

Answer 17

Treat the underlying cause if possible
Diabetes- control the blood glucose
Alcohol- stop alcohol use and replace thiamine

Symptom management
Neuropathic pain- amitriptyline, duloxetine, gabapentin, pregabalin
Foot care, foot wear
Physiotherapy, occupational therapy

Prevent complications
- diabetic foot clinic at least annually, education, footwear

GBS
- IV immunoglobulin, DVT prophylaxis, ventilation if required