Demyelination

Demyelination is the loss or damage of myelin, the insulating wrap around axons in the central nervous system (CNS) and peripheral nervous system (PNS). Myelin speeds electrical impulses; its loss slows conduction or blocks signals. In the CNS, oligodendrocytes form myelin; in the PNS, myelin is produced by Schwann cells. Remyelination is possible but often incomplete.

Demyelination arises in various disorders and conditions. Autoimmune diseases such as multiple sclerosis (CNS) and neuromyelitis optica promote focal demyelinating lesions. Acute inflammatory demyelinating polyneuropathy (Guillain-Barré syndrome) affects the PNS. Genetic or metabolic disorders like leukodystrophies (including adrenoleukodystrophy) cause progressive demyelination. In immunosuppressed individuals, JC virus infection can lead to progressive multifocal leukoencephalopathy with demyelination.

Pathology typically shows patchy loss of myelin with relative axonal preservation early on; gliosis and inflammatory cells are common. Over time, axonal injury may ensue. Remyelination can occur but often yields thinner sheaths and incomplete recovery.

Clinical features depend on the affected area. CNS demyelination may cause visual disturbance, weakness, sensory loss, ataxia, and cognitive change; peripheral demyelination leads to symmetric weakness and numbness. Diagnosis uses MRI to visualize CNS lesions, cerebrospinal fluid analysis for oligoclonal bands, and nerve conduction studies to distinguish demyelinating from axonal neuropathies.

Treatment targets the underlying cause when possible. MS therapies reduce relapses; acute CNS events are often treated with steroids. Guillain-Barré syndrome uses plasmapheresis or IVIG. Across forms, supportive care, rehabilitation, and symptom management are essential. Prognosis varies by disease and the extent of axonal damage.