Polyneuropathy

Long lists of causes of peripheral neuropathy make peripheral nerve disease a dry and uninspiring subjectOverell JR Peripheral neuropathy: pattern recognition for the pragmatist Practical Neurology 2011;11:62-70

This page examines sensory changes caused by involvement of multiple nerves = polyneuropathy.

Pathophysiology

  1. Axonal polyneuropathy (most common)
    • Axons degenerate in distal-to-proximal pattern.
    • Axonal vulnerability is correlated with length; longer axons are the first to be affected, producing LL symptoms/signs, sensory > motor
    • Progresses to weakness of the LL and UL producing a “glove and stocking” sensory loss
    • Can progress to intercostal nerves and sternal sensory loss
    • Causes include:
      • Diabetes
      • Alcohol
      • Amyloidosis
      • Hypothyroidism
      • Vitamin deficiencies (B12, folate)
      • Lyme disease
      • Hereditary Motor and Sensory Neuropathy Type II
  2. Demyelinating polyneuropathy
    • Causes include:
      • Guillain-Bare syndrome
      • Chronic inflammatory demyelinating polyneuropathy (CIDP)
      • Hereditary Motor and Sensory Neuropathy Types I & III (e.g. Charcot-Marie-Tooth)
      • Myeloma
      • Refsum’s = AR peroxisomal disorder leading to an accumulation of phytanic acid
      • POEMS paraneoplastic syndrome = Polyneuropathy, Organomegaly, Endocrinopathy, Myeloma protein, Skin changes
      • HIV

Symptoms

  • Classically the glove and stocking distribution
  • Symmetrical distal sensory loss, burning, with varying degrees of reflex loss or weakness, most commonly LL>UL.
  • Border between normal and absent sensation is usually gradual (in contrast to functional sensory loss)
  • Demyelinating sensory neuropathies tend to produce parasthesia.
  • The figure below summarises modalities commonly affected:

On examination

  • Skin: shiny, dry, hair loss, ulcers (autonomic neuropathy)
    • Skin can appear red, warm and swollen, or pale and cool with autonomic dysfunction.
  • If chronic – Charcot’s joints (loss of pain and proprioception)
  • Ataxia (loss of proprioception)
  • Romberg sign +ve (indicating a sensory ataxia vs. cerebellar ataxia)
  • Painful neuropathy? Likely alcohol related
  • If motor:
    • Wasting, weakness, fasciculations, loss of reflex
    • Plantars downgoing
  • Check postural BP/HR if suspicion of autonomic failure

Often all modalities will be affected. If certain modalities are affected, consider if it is predominantly large fibre or small fibre:

  • Large: loss of vibration/proprioception
  • Small: loss of temperature/pain/autonomic
    • Diabetes, alcohol, amyloid, leprosy, heavy metals, hypothyroid

Diagnosis

  • Bloods
    • FBC, U&E
    • HbA1c, Glucose
    • ESR, CRP
    • LFT
    • TFT
    • B12/folate
    • Serum electrophoresis
    • Autoimmune screen
    • Syphilis, Lyme, HIV
  • CSF
    • Raised protein in CIDP/GBS
  • Nerve conduction
    • Axonal
      • Mostly preserved conduction velocity, CMAP small, distal motor latency normal
    • Demyelinating
      • Reduced conduction velocity, conduction block, CMAP normal, distal motor latency prolonged

Treatments

  • Treat cause
  • Axonal
    • Generally speaking, try to minimise exposure to offending agent
  • Demyelinating
    • Refer to management of CIDP/GBS: intravenous immune globulin, glucocorticoids, and plasma exchange
  • Painful neuropathy
    • Consider trial of gabapentin/carbamazepine/TCA