Peripheral neuropathies

Question 1

What is peripheral neuropathy?

Answer 1

• Disease of the peripheral nerves that can occur at any point in the body.
• This can affects motor, sensory and/or ANS
• It can involve one or multiple i.e. mononeuropathy or polyneuropathy
• Damage can be axonal or demyelinating neuropathies depending on aetiology
• Affects 1 in 10 over 55y.
• Peripheral neuropathy should be considered when a pt comes in presenting with motor and sensory sx.

Question 2

Describe four types of sensory fibres

Answer 2

(1. ) Aα and Aβ are large, myelinated fibres.
(2. ) Αα = signals regarding proprioception
(3. ) Aβ = light touch, pressure, vibration.

(4. ) Aδ and C are small fibres. Both transmit signals regarding pain.
(5. ) Aδ = myelinated, signals about cold sensation
(6. ) C = unmyelinated, signals about warm sensation

Question 3

Causes of mononeuropathies

Answer 3

Can affect anyone although those with diabetes, excess alcohol or toxins, genetic syndromes will be at a predisposition

(1. ) Entrapment neuropathies examples:
- Carpal tunnel syndrome (median nerve)
- Ulnar neuropathy (entrapment at cubital tunnel)
- Peroneal neuropathy (entrapment at fibular head)

(2. ) Cranial mononeuropathies (III or VII cranial nerve palsy)
- Idiopathic, immune mediated, ischemic

Question 4

Causes of polyneuropathy (7)

Answer 4

(1. ) Inflammatory/Immune
- CHRONIC: CIDP and MMN
- ACUTE: GBS
- Others: Vasculitis, rheumatoid arthritis, SLE etc

(2.) Infectious: hepatitis, HIV, Lyme

(3. ) Hereditary
- CHRONIC: Charcot Marie Tooth Disease (CMT), HLPP

(4.) Toxins: Alcohol, pharmaceuticals

(5. ) Systemic medical conditions
- diabetes, renal failure, sarcoidosis, amyloidosis, hypothyroidism, gluten sensitivity / coeliac disease

(6.) Vitamin deficiency (commonly B12)

(7. ) Idiopathic
- Chronic idiopathic axonal polyneuropathy

Axonal PN Causes = Vasculitis, DM, Sarcoidosis, infection (HIV, hepatitis etc), CIAP, alcohol
Demyelinating PN Causes = MMN, CMT, CIDP, GBS etc

Question 5

Clinical Features of AXONAL PN (3)

Answer 5

PN typically starts by affecting longest peripheral nerves first so Sx typically affect distal before upper limbs. Can be categorised in the following:

(1. ) Symmetrical sensorimotor/sensory neuropathies
- Longer fibres are affected first
- Initially sensory, but eventually sensorimotor
- Commonest type of neuropathy
- Usually sensory sx: tingling, burning etc, and eventually moves higher up

(2. ) Asymmetrical Sensory/sensory ganglionopathies
- Dorsal root ganglia is affected
- Purely sensory
- Presents with patchy distribution of Sx
- Associated with: paraneoplastic, Sjogren, Gluten sensitivity, Coeliac

(3. ) Asymmetrical sensorimotor neuropathies/mononeuritis multiplex
- Multiple nerve involvement
- sensorimotor + asymmetrical + randomly affect any nerve without specific pattern.
- Sx: Right arm (median is affected), little finger (ulnar nerve), leg, foot
- Painful and occurs in the context of vasculitis.

Question 6

Guillain barre syndrome (GBS): what is it? Sx? Ix? Tx?

Answer 6

(1. ) Immune mediated ACUTE demyelinating ascending PN.
- Leads to weakness in arm and legs and can lead to RESP FAILURE. Affects both motor and sensory.
- Often triggered by infection (campylobacter, EBV).

(2. )
- Symmetrical ascending weakness starting in feet
- Paraesthesia, neuropathic pain
- Dec reflex (remember it is a PN so LMN lesion)
- Bell palsy
- As it progresses: bulbar, respiratory weakness
- RAPID DETERIORATION TO RESP FAILURE

(3. ) Ix
- Bedside spirometry (FVC) is essential***
- Nerve conduction Studies: reduced signal
- LP show a raised protein
- GM1 Abs (25%)

(4. ) Mx
- ITU
- Plasma exchange + IV Ig
- Ventilation
- VTE prophylaxis (LMWH) to prevent blood clots as PE is leading cause of death in GBS

Question 7

What Sx may be seen in motor, sensory, autonomic neuropathies?

Answer 7

(1. ) Motor nerve involvement like LMN lesions
- Muscle cramps
- Weakness
- Fasciculations
- Atrophy
- High arched feet

(2. ) Small-fibre neuropathies = burning pain sensation, loss of touch, vibration etc
(3. ) Autonomic involvement = postural hypotension, disturbance of sweating, cardiac rhythm, gastrointestinal, bladder and sexual dysfunction

Question 8

Ex + Ix of peripheral diseases

Answer 8

Examination:
Hallmarks of PN is the sensory impairment and the diminished or absent reflexes
- Reduced or absent tendon reflexes
- Sensory deficit
- Weakness + muscle atrophy 

Nerve Conduction Studies

• Key in discriminating between demyelinating and axonal neuropathies, and in identifying entrapment neuropathies
• Demyelinating = reduced conduction velocities or conduction block
• Axonal = reduced amplitudes of potentials

Question 9

Tx of Peripheral Neuropathies

Answer 9

Aim is to identify any reversible cause and stop progression if possible.

Symptomatic Tx in Chronic:

• Pain (i.e. amitryptilline, gabapentin, pregabalin etc)
• Cramps (i.e. quinine)
• Balance (i.e physiotherapy/ walking aids)

Question 10

GBS clinical features

Answer 10

(1. ) Motor weakness – often distal and ascending
(2. ) Paraesthesia
(3. ) Respiratory involvement
(4. ) Autonomic involvement – HR changes, BP changes, urinary control symptoms
(5. ) serology - ab present