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