Peripheral nerve disorders

Nerve Injury & Repair - Anatomy Under Attack

• Nerve Sheaths

  • Epineurium: Dense connective tissue covering the entire peripheral nerve.
  • Perineurium: Surrounds nerve fascicles; forms the blood-nerve barrier.
  • Endoneurium: Surrounds individual axons and their Schwann cells.

• Seddon Classification of Nerve Injury

• Wallerian Degeneration & Regeneration

⭐ Axonal regeneration in the PNS occurs at a rate of approximately 1 mm/day or 1 inch/month.

Guillain-Barré Syndrome - Ground-Up Invasion

• Acute, immune-mediated demyelinating polyneuropathy, often post-infection (Campylobacter jejuni, viruses).
  • Pathogenesis involves molecular mimicry, targeting peripheral nerve myelin or axons.

• Clinical: Rapidly progressive, symmetric ascending weakness (📌 "ground-to-brain").
  • Starts in legs, ascends to arms, trunk, and face.
  • ↓ or absent deep tendon reflexes.
  • Autonomic dysfunction (tachycardia, BP changes) and respiratory failure are life-threatening complications.
• Diagnosis & Management:
  • Nerve conduction studies show slowed velocity.
  • Treatment: IV immunoglobulin (IVIG) or plasmapheresis.

⭐ Key finding is albuminocytologic dissociation in CSF: markedly ↑ protein with a normal cell count, typically seen after the first week.

Chronic Neuropathies - Slow Burn & Wreckage

• Diabetic Neuropathy: Most common cause of peripheral neuropathy.

  • Pathogenesis: Metabolic & vascular damage from chronic hyperglycemia. ↑Advanced glycation end products (AGEs) & sorbitol, ischemic injury to vasa nervorum.
  • Clinical: Distal, symmetric sensory or sensorimotor "stocking-and-glove" pattern. Autonomic neuropathy (gastroparesis, orthostatic hypotension) is common.
  • Morphology: Axonal degeneration. Hyalinization of endoneurial arterioles.

• Charcot-Marie-Tooth (CMT) Disease: Most common hereditary peripheral neuropathy.

  • Pathogenesis: Genetic defects in myelin- or axon-related proteins (e.g., PMP22 duplication in CMT1A).
  • Clinical: Distal muscle atrophy (e.g., peroneal), sensory loss, pes cavus ("stork leg" deformity).
  • Morphology: Repetitive demyelination & remyelination forms concentric layers of Schwann cells.

⭐ Exam Favorite: The characteristic finding in demyelinating forms of CMT is "onion bulb" formation, visible on nerve biopsy, resulting from cycles of Schwann cell proliferation.

High‑Yield Points - ⚡ Biggest Takeaways

• Guillain-Barré syndrome is an acute, ascending paralysis, often post-Campylobacter infection, with albuminocytologic dissociation in CSF.
• Diabetic neuropathy, the most common type, manifests as a distal, symmetric "stocking-glove" sensory loss.
• Charcot-Marie-Tooth is a hereditary motor-sensory neuropathy causing pes cavus and distal muscle atrophy.
• Wallerian degeneration refers to axonal breakdown distal to injury, with debris cleared by macrophages.
• Segmental demyelination from Schwann cell damage slows nerve conduction velocity, a key feature in GBS.