• Clinical science

Polyneuropathy

Abstract

Polyneuropathy is a systemic disease which involves damage to multiple peripheral nerve fibers. The condition can be caused by diabetes mellitus, alcoholism, hereditary diseases, toxins, infectious or other inflammatory conditions. The classic presentation is a symmetric distal sensory loss or burning sensation associated with motor weakness. Further clinical features depend on whether an axonal or demyelinating nerve injury has occurred. Diagnostic tests, usually beginning electrodiagnostic testing, are indicated in patients with atypical clinical features, unknown etiology, and/or severe or rapidly progressive symptoms. Therapy includes treatment of the underlying disorder and symptomatic therapy (e.g., control of neuropathic pain).

Etiology

References:[1][2][3][4][5][6][7][8][9]

Clinical features

General

  • Symmetric distal sensory loss or burning and motor weakness (most common presentation)
    • Burning-foot syndrome: ↓ fine touch, vibration: , pain; , tingling, pins-and-needles sensation or formication . Distribution most often in a distal and symmetric pattern (glove and stocking pattern)
    • Atrophy and paresis of muscles (e.g., “stork-legs” in the case of HMSN type I)
    • Ataxia (e.g., sensory ataxia due to vitamin B12 deficiency)
    • Deep tendon reflexes

Axonal vs Demyelinating

Axonal Demyelinating
Chronic Acute Chronic Acute
Natural history
  • Slow decline over years
  • Months to years of slow, yet incomplete recovery
  • Variable (periods of recovery, stabilization, exacerbations, or slow decline)
  • Variable
Characteristics
  • Affects longer axons first (begins in lower extremitiessternum (intercostal nerves) → head)
  • Early disease: sensory symptoms > motor symptoms
  • Similar, but symptoms more severe
  • Significant pain
  • Early disease: motor symptoms = sensory symptoms
  • Early disease: motor symptoms > sensory symptoms
  • Distal muscle wasting: feet, lower legs, hands (severe cases)
  • Distal sensory loss (pain, temperature, proprioception, vibration)
  • Reduced or absent distal reflexes (usually begins in the ankles)
  • Generalized muscle weakness: distal > proximal
  • Diffusely reduced or absent reflexes

References:[10][11][12][9]

Subtypes and variants

Diabetic polyneuropathy

  • Definition: progressive peripheral nerve injury due to chronic hyperglycemia
  • Clinical features
    • Sensory deficits
    • Cranial nerve involvement is very common (especially of the oculomotor and abducens nerve)
    • Trophic skin changes; (due to autonomic neuropathy; ): anhidrosis; , edema, ulcers
    • Autonomic features: erectile dysfunction, gastric atony; , postprandial diarrhea, tachycardia at rest, impaired pupillary tone
    • Diabetic amyotrophy: initially painful proximal muscle weakness; distal sensory loss may occur
  • Treatment: control of blood glucose and foot care

Alcoholic polyneuropathy

Hereditary motor sensory neuropathies

References:[13][12][14][15][16][17][18][19][20][21][22][23][24][25][26]

Diagnostics

Further tests are usually indicated in patients with atypical clinical features, an unknown etiology, and/or severe or rapidly progressive symptoms.

  • Electrodiagnostic testing
    • Nerve conduction studies on the sural nerve: to determine the type of neuropathy and with it the possible cause
      • Primary demyelination = ↓ impulse conduction velocity, normal amplitude
      • Axonal degeneration = normal impulse conduction velocity, ↓ amplitude
    • Electromyography; (EMG): e.g., spontaneous electrical activity at rest; (denervation potentials) in the case of axonal degeneration
  • Laboratory tests (selection depends on the suspected underlying disorder)
  • If necessary: nerve-muscle biopsies (useful to identify a small fiber sensory neuropathy or infiltrative disorders), skin biopsy (useful to identify small fiber sensory neuropathies), molecular genetic tests for suspected hereditary disorders

References:[27][9][28][29]

Differential diagnoses

References:[30][31]

The differential diagnoses listed here are not exhaustive.

Treatment

Treatment efficacy can only be assessed after 2–4 weeks of therapy! Since complete pain relief is often not possible, a tolerable level of pain can be an acceptable treatment goal!

The patient can be weaned off medications slowly after one year or once the underlying cause has been effectively treated (e.g., optimal control of serum glucose levels in cases of diabetic neuropathy)!

References:[9][32][33][34]