Neuropathy

Nicholas Mallett

Background 

  • Peripheral neuropathy is damage to peripheral nerves. Classical polyneuropathy is slow, chronic, progressive sensory loss in length-dependent fashion.
  • Common etiologies of polyneuropathy: Diabetes, chronic EtOH use, Vitamin Deficiencies/Toxicities, chronic HIV/HBV/HCV, Amyloidosis, Monoclonal Gammopathies, Hypothyroidism, Autoimmune, Medication-related/Iatrogenic, and Critical Illness.
  • Mononeuropathy: sensory +/- motor symptoms in a single peripheral nerve distribution (ie carpel tunnel). Can be from local trauma, compression, entrapment.
  • Radiculopathy is from spine nerve root localization (ie L4), polyradiculopathy if multiple, plexopathy is process affecting multiple nerves in brachial or lumbosacral plexus.
  • Large Fiber Neuropathy: loss of vibration sense/proprioception.
  • Small Fiber Neuropathy: loss of pain/temperature sensation – cannot be dx by EMG/NCS.

Evaluation 

  • Usually diagnosed clinically based on examination and history.
  • Polyneuropathy presents with slow, progressive sensory loss in the classic “stocking and glove” distribution, usually beginning in the lower extremities.
  • Many patients don’t realize numbness until very symptomatic (can’t feel car pedals, burning pain, gait disturbances, etc). Can have +Romberg, falls in dark due to poor proprioception.
  • Reduced reflexes on examination.
  • In cases where exam is not sufficient, EMG/NCS can aid in diagnosis.
  • Important to determine etiology behind neuropathy to determine if able to stop/slow progression.
  • Basic lab work: A1c, B12 (<400 can cause symptoms), SPEP+FLC and Immunofixation.

Management 

  • No treatment to reverse numbness, aim to treat pain if needed.
  • Address underlying etiology to prevent progression.
  • If rapidly progressive, consider referral to Neurology for evaluation.
  • Neuropathic pain management:
    • Gabapentin/Pregabalin – PROS: antiseizure benefits, headache treatment; CONS: dizziness, drowsiness.
    • Duloxetine – PROS: anxiety/depression effect, migraine prophylaxis; CONS: risk of Serotonin Syndrome/Mania.
    • Amitriptyline – PROS: depression treatment, headache prophylaxis; CONS: anticholinergic effects.
    • Alpha Lipoic Acid – relatively benign OTC supplement with antioxidant properties shown to reduce nerve hypoxia with diabetic neuropathy.
    • Topicals: Lidocaine, Capsaicin.
    • Would avoid prescribing opioids for neuropathic pain as they have little benefit.
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