La d A middle-aged female patient presented with slowly progressive motor weakness, nuchal rigidity, and difficulty in swallowing and carrying out day-to-day activities. A provisional diagnosis of multiple sclerosis is suspected. Which of the following cells are affected in multiple sclerosis?

Correct Answer: D. Oligodendrocytes

Multiple sclerosis (MS) is a demyelinating autoimmune disease of the central nervous system (CNS) characterized by selective destruction of myelin sheaths that insulate axons. The primary target cells in MS are oligodendrocytes, which are the myelin-producing glial cells in the CNS. Each oligodendrocyte extends multiple processes to myelinate segments of several axons simultaneously, forming the myelin sheath that enables rapid saltatory conduction. In MS, autoreactive T cells and B cells infiltrate the CNS and attack oligodendrocytes and myelin, leading to demyelination plaques (lesions) scattered throughout the brain and spinal cord. This demyelination disrupts action potential propagation along axons, causing the progressive neurological deficits seen in this patient: motor weakness (pyramidal tract involvement), nuchal rigidity (brainstem/cervical cord involvement), and dysphagia (bulbar involvement). The clinical presentation—slowly progressive course with multifocal CNS involvement—is pathognomonic for MS. While other glial cells may be secondarily involved in the inflammatory cascade, oligodendrocytes are the primary and specific target of the autoimmune attack in MS. This distinguishes MS from other demyelinating conditions and explains why oligodendrocyte dysfunction is the fundamental pathological mechanism.

Why the other options are wrong

A. Ependymal cells — Ependymal cells line the ventricular system and produce cerebrospinal fluid; they are not involved in myelination. While MS plaques may occur near ventricles, ependymal cells are not the primary target. This is a distractor that confuses CNS location with pathological mechanism. B. Astrocytes — Astrocytes provide metabolic support and form the blood-brain barrier but do not produce myelin in the CNS. Although astrocytes participate in the inflammatory response and gliosis during MS, they are secondary responders, not the primary target. NBE may use this to confuse students who know astrocytes are important glial cells. C. Microglia — Microglia are CNS-resident macrophages that participate in immune surveillance and phagocytosis of myelin debris during MS. However, they are effector cells in the inflammatory cascade, not the primary target of autoimmune attack. Confusing microglia with oligodendrocytes is a common trap for students who focus on inflammation rather than demyelination.

High-Yield Facts

Mnemonics

CNS Myelin Producer = OLIGO Oligodendrocytes = One cell type that makes myelin in CNS. Remember: Oligo = few (one oligodendrocyte myelinates many axons, unlike PNS Schwann cells which are 1:1). Use when distinguishing CNS vs PNS demyelination. MS = Myelin + Oligodendrocytes Suffer MS attacks myelin → oligodendrocytes die → demyelination → conduction block. When you see 'demyelinating disease of CNS,' think oligodendrocytes first.

NBE Trap

NBE pairs MS with 'glial cells' broadly to lure students into choosing astrocytes or microglia, which are indeed involved in MS inflammation but are not the primary target. The trap is conflating secondary inflammatory response with primary pathology—oligodendrocytes are the specific autoimmune target, not just any glial cell.

Clinical Pearl

In Indian clinical practice, MS is less common than in Western populations but is increasingly recognized in young adults presenting with optic neuritis or transverse myelitis. The key bedside insight is that demyelination causes conduction block (not just slowing), which explains why MS patients often have sudden, severe deficits that may partially recover as inflammation resolves and remyelination begins—a feature that distinguishes MS from axonal degeneration diseases like ALS.

_Reference: Robbins & Cotran Pathologic Basis of Disease, Ch. 28 (CNS Demyelinating Diseases); Harrison's Principles of Internal Medicine, Ch. 380 (Multiple Sclerosis)_