A peripheral nerve biopsy shows concentric layers of myelin forming multiple lamellae around an axon ('onion bulb' appearance) on light microscopy. This histological finding is characteristic of which condition?

• A Guillain-Barré syndrome (acute inflammatory demyelinating polyneuropathy)
• B Diabetic peripheral neuropathy
• C Charcot-Marie-Tooth disease (hereditary motor and sensory neuropathy) ✓
• D Amyloid neuropathy

Explanation

Onion bulb formations in peripheral nerve biopsies result from repeated cycles of demyelination and remyelination, causing concentric proliferation of Schwann cells around an axon. This is the hallmark of hereditary hypertrophic neuropathies, particularly Charcot-Marie-Tooth disease type 1 (CMT1, HMSN Type I), where mutations in myelin proteins (PMP22, MPZ, connexin-32) cause chronic demyelination. Palpably enlarged peripheral nerves (hypertrophic neuropathy) result. GBS shows acute inflammatory demyelination with macrophage infiltration but not onion bulbs. Diabetic neuropathy shows axonal degeneration and basement membrane thickening.

Reference: BD Chaurasia's Human Anatomy, 8th ed.

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Written and medically reviewed by the StethoPrep medical team.