10.11.3 Peripheral Neuropathies

Question 1

Classify polyneuropathies

Answer 1

Acute/subacute polyneuropathies
- Time to nadir
— < 4 weeks: acute
— 4-12 weeks: subacute
- Often reversible

Chronic polyneuropathies
- Time to nadir > 12 weeks —
- Often not reversible

Question 2

Causes of acute polyneuropathy

Answer 2

• Guillain-Barré syndrome
• Porphyria
• Thiamine deficiency neuropathy
• Severe hyperkalaemia

Question 3

Causes of subacute polyneuropathies

Answer 3

• Thiamine deficiency neuropathy
• Paraneoplastic neuropathy

Question 4

Causes of chronic polyneuropathies

Answer 4

• Diabetic polyneuropathy
• Toxic polyneuropathies (Alcohol; Medications)
• HIV infection
• Inflammatory (CIDP;Paraproteinemic)
• Nutritional / vitamin deficiencies
• Hereditary
• Other systemic diseases (Chronic renal failure)

Question 5

Symptoms of polyneuropathies

Answer 5

Symptoms
- Sensory: numbness, paresthesias, pain, ̄ temperature or pain
sensation
- Motor: weakness, clumsiness, incoordination

Signs
- Distal sensory loss, distal weakness, distal reflex loss

Question 6

Guillian-Barré Syndrome - acute/ subacute polyneuropathies
Pathogenesis
Types x2

Answer 6

Post-infectious illness:
- Respiratory tract or GIT
- 3 days - 6 weeks after infection
- Reported by 2/3 patients
- Mechanism: “molecular mimicry”

1. AIDP - Acute inflammatory demyelinating polyneuropathy
- Inflammatory attack on myelin sheath
- Commonest form of GBS (± 90%) —

2. Axonal forms (AMAN & AMSAN)
- Antibody-mediated attack at nodes of Ranvier
- About 10% of cases

Question 7

Guillian-Barré Syndrome
Clinical

Answer 7

• Proximal and distal weakness with areflexia (absent reflexes)
• No / minimal sensory symptoms
• Usually no sphincter dysfunction
• Cranial nerve dysfunction —
  ➡️Most often facial weakness

Question 8

GBS and HIV infection

Answer 8

• GBS more common in HIV-infected people
• Clinical features similar
• CSF findings similar, except for the presence of up to ± 100 lymphocytes
• Treatment similar
• Outcome appears to be similar

Question 9

GBS outcome

Answer 9

2-8% mortality rate

Survivors:
- 70 % recover completely / minimal symptoms
- 20% unable to run
- 8% unable to walk unassisted —
- 2% bedridden

Question 10

Porphyria

Answer 10

• Group of inherited disorders of haem synthesis

Clinically
- Abdominal pain
- ± skin lesions
- Seizures and delirium
- Polyneuropathy with global weakness — (Acute intermittent porphyria; Porphyria variegata)

Question 11

Paraneoplastic neuropathy

Answer 11

• Subacute sensory (ataxic) (or sensorimotor) neuropathy —
• Not painful
• Often presents before the cancer
• Thus:
  — Subacute sensory neuropathy: aggressive search for cancer

Question 12

Diabetic polyneuropathy
General
Clinical features
Complications

Answer 12

• ⬆️ incidence with ⬆️ duration of diabetes

Clinical features
- Insidious onset of numbness, paresthesias, burning pain, hyperesthesia
- Slow progression over years
- Starts distally, progresses proximally
- Sensory complaints most frequent
- Motor involvement (less frequent and later)
- Often associated carpal tunnel syndrome

Sensory loss may lead to
- Repetitive trauma to skin, bone, joints (Charcot joints) —
- Impaction of foreign objects
- Foot ulcers
- Sepsis