What is the underlying pathophysiology of multiple sclerosis?

• A. Autoimmune demyelination of CNS neurons with inflammatory lesions
• B. Neuron death from ischemia
• C. Bacterial infection causing neuropathy
• D. Genetic deficiency of myelin basic protein

Answer: (A)

Multiple sclerosis is an autoimmune inflammatory demyelinating disease of the central nervous system. The immune system targets myelin sheaths around CNS axons, triggering inflammatory lesions and loss of myelin. Autoreactive T cells cross the blood-brain barrier, activating microglia and macrophages and releasing cytokines that damage oligodendrocytes and myelin. This disrupts saltatory conduction along affected fibers and leads to the diverse neurologic symptoms seen, which may recover partially but can leave residual deficits as plaques form and remyelination becomes incomplete. The pattern of lesions in well-defined CNS regions explains optic neuritis, sensory and motor deficits, gait disturbances, and other focal signs, and the disease often follows relapsing-remitting or progressive courses.

Other options don’t fit MS because neuron death from ischemia reflects vascular stroke rather than autoimmune demyelination; bacterial infection causing neuropathy is an infectious process, not primary demyelination by autoimmunity; and a genetic deficiency of myelin basic protein would be a congenital disorder, not an autoimmune CNS demyelinating disease.