Onion bulb formation

What it means

Repeated episodes of segmental demyelination and remyelination lead to the accumulation of supernumerary Schwann cells around axons, which is referred to as onion bulb formation. This finding affects peripheral nerves.

This feature is characteristic of chronic demyelinating neuropathies as well as certain hereditary neuropathies. Onion-bulb formation may be observed in electron microscopic examinations of peripheral nerve biopsy material. Often, this examination is performed on the sural nerve.

Rare diseases that can present with this2

The range is how often this sign appears among people diagnosed with each disease — it is not a probability of having any of them. Many of these signs also occur in common, non-rare conditions. A sign on this page is a conversation to have with a clinician, not a conclusion.

Part of the broader category

Also called: Onion bulb formations