Description

• Defined as pain caused by direct nerve injury in either peripheral or central nervous system
• Can exist without ongoing disease
• Can arise from damage to nerve pathways at any point from terminals of the peripheral nociceptors to cortical neurons in the brain
• Causes include traumatic nerve injury, infection, metabolic injury, autoimmune disease, neoplasm, drugs, radiation, and neurovascular disorders.

Epidemiology

Includes chronic conditions that affect up to 10% of the population

• Cancer—up to 20% have neuropathic pain from either cancer or treatment
• Herpes zoster—lifetime incidence is ~25%. Up to 10% develop chronic postherpetic neuralgia.
• HIV—33 million people infected across the world; ~35% have neuropathic pain.
• Diabetic neuropathy—affects 0.8% of population

Etiology and Pathophysiology

• Positive symptoms due to changes in peripheral nerves, loss of inhibitory mechanisms in central nervous system (CNS), and central sensitization
• Negative symptoms (sensory deficits) reflect neural damage.
• Associated with numerous conditions, including:
  • Demyelinating disorders (multiple sclerosis, Guillain-Barré syndrome)
  • Neoplasm (primary/metastatic)
  • Neurovascular (central poststroke syndrome, diabetes, trigeminal neuralgia)
  • Autoimmune disease (Sjögren syndrome, polyarteritis nodosa)
  • Structural disease (herniated disc disease) (1)

Risk Factors

• General risk factors include older age, female gender, physical inactivity, and manual occupation.
• There is growing evidence of genetic factors.
• Includes conditions that cause nerve damage or potentiate symptoms from damaged nerves:
  • Diabetes
  • Herpes zoster
  • Trigeminal neuralgia
  • HIV
  • Lyme disease
  • Cancer and chemotherapy
  • Stroke
  • Multiple sclerosis
  • Trauma
  • Surgery
  • Limb amputation
  • Nutritional deficiencies
  • Medications

Commonly Associated Conditions

• Depression/anxiety: presence worsens quality of life significantly
• Insomnia
• Substance abuse