Question

Which is the correct explanation for "onion bulb" formation in CIDP? a. Macrophages phagocytose myelin debris b. Abundant T-cell apoptosis c. Repetitive De- and Remyelination with Schwann cell proliferation d. Nitric oxide release e. Genetic myelin deficiency

Short answer

Answer: The primary cause of onion bulb formation in CIDP is repetitive demyelination and remyelination with Schwann cell proliferation.

Step-by-step solution

Introduction to Onion Bulb Formation

Onion bulbs are a histopathological feature seen in CIDP, characterized by concentric layers of Schwann cells around axons as a result of recurrent demyelination and remyelination.

Option a: Macrophages Phagocytose Myelin Debris

Macrophages play a role in the clearance of myelin debris after demyelination but do not directly contribute to onion bulb formation.

Option b: Abundant T-Cell Apoptosis

T-cell apoptosis is a process that takes place during the immune response, but it is not a primary cause of onion bulb formation in CIDP.

Option c: Repetitive De- and Remyelination with Schwann Cell Proliferation

The repetitive demyelination and remyelination in CIDP lead to onion bulb formation. This process involves the proliferation of Schwann cells, which try to repair the damaged myelin sheath by forming multiple layers around the affected axons.

Option d: Nitric Oxide Release

Nitric oxide is an important signaling molecule involved in many physiological processes, but it is not related to onion bulb formation in CIDP.

Option e: Genetic Myelin Deficiency

While genetic myelin deficiencies may be the cause of some demyelinating diseases, CIDP is primarily an autoimmune disorder and is not directly caused by a genetic myelin deficiency.

Correct Explanation for Onion Bulb Formation in CIDP

Based on the above analysis, the correct explanation for onion bulb formation in CIDP is option c, which states "Repetitive De- and Remyelination with Schwann cell proliferation." Therefore, the answer is c.

Key concepts

Onion Bulb Formation

In Chronic Inflammatory Demyelinating Polyneuropathy (CIDP), one of the hallmark features often observed under the microscope is the formation of structures known as onion bulbs. This phenomenon results from repetitive cycles of demyelination and remyelination. Over time, Schwann cells, which are responsible for producing the myelin sheath around neurons, undergo proliferation to repair the damage.
These Schwann cells create multiple layered formations around the nerve fibers, akin to the layers of an onion, hence the name "onion bulb." This layering attempts to restore the compromised myelin sheath, but the continual cycle of damage and repair leads to this distinctive onion-like appearance.

• Onion bulb formation is indicative of chronic nerve damage.
• It reflects the body's attempt to mitigate the effects of myelin loss.
• It showcases the persistent regenerative efforts of Schwann cells.

The identification of onion bulbs is essential for diagnosing CIDP, highlighting the need for detailed microscopic examination in affected individuals.

Schwann Cell Proliferation

Schwann cells are crucial components in the peripheral nervous system. They produce the myelin sheath that insulates axons, facilitating efficient transmission of electrical signals. In the context of CIDP, Schwann cell proliferation is part of a compensatory mechanism to repair demyelinated axons.
During episodes of nerve injury, Schwann cells re-enter the cell cycle to produce new layers of myelin. This proliferation, while aimed at repairing damaged nerves, can sometimes lead to the formation of abnormal layers around the axon.

• The process is initiated by signals indicating nerve damage.
• Schwann cell proliferation is crucial for nerve regeneration.
• This mechanism is often insufficient in rapid myelin reconstruction.

Despite their regenerative efforts, Schwann cells in CIDP face the challenge of repeatedly restoring the myelin sheath due to ongoing immune-mediated damage, reflecting the chronic nature of the disease.

Demyelination and Remyelination

Demyelination and remyelination are central processes in CIDP. Demyelination involves the loss of the myelin sheath surrounding nerve fibers, predominantly caused by immune system attacks. This leads to the impairment of nerve conduction, manifesting clinically as muscle weakness and sensory dysfunction.
Remyelination, on the other hand, is the body's natural response to repair and restore the damaged myelin sheath. This involves the proliferation of Schwann cells, which begin to migrate, align around the axon, and produce new myelin layers.
In CIDP, the cycle of demyelination and subsequent remyelination is continuous, leading to variable nerve function outcomes.

• Demyelination reduces nerve signal speed and efficiency.
• Remyelination attempts to restore normal nerve function.
• In CIDP, immune dysregulation causes repeated demyelination.

These cycles can eventually cause permanent nerve damage if not adequately managed, making early diagnosis and treatment of CIDP imperative.