Polyneuropathy

Basics

A peripheral nerve disorder in which many nerves throughout the body malfunction simultaneously
Typically affects distal nerves most prominently
Acute polyneuropathy causes:
- Infectious:
  - Toxin-producing bacteria
  - Viruses
- Autoimmune:
  - Guillain–Barré syndrome (GBS)
- Toxic (heavy metals):
  - Lead
  - Mercury
- Drugs:
  - Anticonvulsants (phenytoin, lithium)
  - Antibiotics (dapsone, isoniazid, metronidazole, nitrofurantoin, sulfonamides)
  - Chemotherapy (oxaliplatin, paclitaxel)
  - Sedatives (hexobarbital and barbital)
Cancer:
- Multiple myeloma
- Direct tumor invasion
- Postradiation or surgery
Chronic polyneuropathy causes:
- Diabetes (most common)
- Alcohol abuse
- Nutritional deficiencies:
  - Thiamine
  - B₁₂
- HIV
- Hypothyroidism
- Liver failure
- Kidney failure
- Lung cancer
- Chronic inflammatory demyelinating polyneuropathy (CIDM)

In the US, the prevalence of polyneuropathy is ∼2% in the general population
It is 8% in patients > 55 yr of age
The most common cause in the US is diabetes and it occurs in ∼50% of diabetics on insulin

Myelin dysfunction:
- Parainfectious immune response triggered by antigens that cross-react with antigens in the peripheral nervous system:
  - Encapsulated bacteria:
    - Campylobacter sp
    - Diphtheria
  - Viruses:
    - Enteric
    - Influenza viruses
    - HIV
  - Vaccines:
    - Influenza
- GBS:
  - Acute onset due to myelin dysfunction
  - Rapidly progressive weakness and may lead to respiratory failure
- CIDM:
  - Chronic illness of myelin dysfunction
  - Symptoms may recur or progress over months and years
Oxidative stress:
- As the myelin begins to regenerate, sodium channel receptors can become altered, leading to reduced resting potential and increased ectopic impulses
Vasa nervosum compromise:
- Vascular supply to nerves compromised leading to nerve infarction and electrical instability
- Primary dysfunction of the axon
- Most often the result of toxic–metabolic disorders:
  - Diabetes
  - Nutritional deficiencies
  - Drugs/chemicals

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