Peripheral Neuropathy

Basics:

  • One axon -> covered by endoneurium
  • Multiple axons make up a fascicle which is covered by perineurium
  • Multiple fascicles + blood vessels -> covered by epineurium

 

Classification of peripheral neuropathy:

  • Mononeuropathy: single nerve; median N in CTS
  • Mononeuritis multiplex: single nerves in multiple locations with asymmetrical pattern (vasculitis)
  • Polyneuropathy: multiple nerves contiguous or symmetrical, typically length dependent (meaning they affect longest fibers first) -> “stocking-glove” distribution
  • Examples: DM (most common), toxins, HIV, SLE, alcohol, vit B12 def, uremia

 

Negative symptoms Positive symptoms Examples
Motor Weakness, hyporeflexia, wasting, hypotonia, deformity Fasciculations, cramps GBS, lead toxicity, Charcot-Marie-Tooth
Sensory Large fibers ↓ vibration, proprioception, reflexes, ataxia Paresthesia Paraneoplastic, vit B6 toxicity
Small fibers ↓ pain, temperature Dysesthesias, allodynia DM, amyloid, drugs (vincristine)
Autonomic ↓ sweating, BP, urinary retention, impotence, vascular color changes ↑ sweating, BP

 

  • B6 def or toxicity, cancer, amyloid, HIV, cisplastin\chemo, Sjogren -> affect dorsal root ganglion
  • Sensorimotor axonal polyneuropathy: alcohol, DM, hypothyroid, uremia, B12 def, monoclonal gammopathy
  • Allodynia: excessive pain as a response to a non-painful ordinary stimulus -> migraine, peripheral neuropathy
  • Clues for inherited neuropathy: deformities, long duration, indolent progression, few positive symptoms, family Hx

 


Axonopathy:

  • Axonal degeneration
  • On exam: weakness + atrophy
  • Length dependent -> legs more than arms
  • Example: DM
  • NCS: decreased CMAP amplitude
  • Worse prognosis, more common

 

Myelinopathy:

  • On exam:
    • Weakness, but no atrophy, global arreflexia
    • Hypertrophic nerves? Bc of the repeated process of demylination – remyelination (esp peroneal or post auricular N)
  • Examples: GBS, CIDP, Charcot-Marie-Tooth
  • Charcot-Marie-Tooth is initially a myelinopathy, but they develop secondary axonopathy
  • Histopathology:
    • Cross section: onion bulb
    • Longitudinal: teased fiber
  • NCS: decreased conduction velocity, conduction block or temporal dispersion
  • EMG: reduced recruitment w\out much denervation
  • Better prognosis

 


Diabetic Peripheral Neuropathy: 

  • Typical (most common type): distal symmetrical sensorimotor polyneuropathy -> painful
  • Atypical: asymmetry or prox more than dist, motor involvement
  • Autonomic: gastroparesis, resultants diarrhea, arrhythmia and postural hypotension
  • CN: isolated 3rd (pupil sparing) > 4th > 6th
  • As soon as they develop neuropathy, it will continue to progress even if you tell the pt to tightly control their blood sugar

 


Guillian Barre Syndrome (GBS): ‘the peripheral form of MS’

  • Acute, motor and sensory (large fiber), length dependent, preceded by illness\infection (most common is campylobacter jejuni)
  • Pathogenesis: molecular mimicry
  • Clinical:
    • Sensory: distal + symmetrical paresthesia, loss of proprioception and vibration, neuro pain
    • Motor: distal weakness, areflexia. Resp muscls (diaphragm) weakness is the main issue
    • Autonomic: hypo\hyper-tension, arrhythmia, bladder dysnfunx
  • Types:
    • Acute inflammatory demyelinating polyneuropathy (AIDP) -> most common worldwide
    • Other axonal types (AMSAN, AMAN) -> most common in Saudi
  • CSF: “albuminocytologic dissociationhigh protein (albumin) but normal WBCs? Demyelination in the roots, myelin secretes protein in CSF, not infectious process
  • NCS: decreased motor nerve conduction velocity
  • Variant: Miller Fisher Syndrome: triad: opthalmoplegia, areflexia, ataxia (anti-GQ1b)
  • Treatment:
    • ABCs + monitor for resp failure and arrhythmia (cause of death)
    • No role for steroids!
    • IVIG or plasma exchange (equally effective)

 


Chronic Inflammatory Demyelinating Polyneuropathy (CIDP): the chronic form of GBS’

  • Chronic relapsing sensorimotor polyneuropathy with increased protein in CSF and demyelination
  • Course is fluctuating (in contrast w\ GBS)
  • Treatment: 1st line -> prednisone

 


Download the PDF version: here


References:

  • Dr Ali Alshehri’s lecture notes
  • Toronto notes
  • Step up to medicine

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