Multiple sclerosis

Multiple sclerosis
Name	Multiple sclerosis
Synonyms	Disseminated sclerosis, encephalomyelitis disseminata
Caption	An MRI scan showing characteristic lesions in the white matter of the brain.
Field	Neurology
Symptoms	Numbness, weakness, vision problems, fatigue, cognitive impairment
Complications	Mobility issues, depression, epilepsy
Onset	Typically 20–50 years of age
Duration	Long-term
Types	Relapsing-remitting, secondary progressive, primary progressive, progressive relapsing
Causes	Unknown (combination of genetic and environmental factors)
Risks	Family history, certain infections, low vitamin D, smoking, living far from the equator
Diagnosis	Based on symptoms, medical tests, MRI scans
Differential	Neuromyelitis optica, sarcoidosis, Lyme disease
Prevention	Unknown
Treatment	Disease-modifying therapies, steroids, physical therapy
Medication	Interferon beta-1a, natalizumab, fingolimod, ocrelizumab
Prognosis	Variable; often reduced life expectancy
Frequency	~2.8 million globally (2020)
Deaths	Rarely directly fatal

Multiple sclerosis. It is a chronic autoimmune disease that affects the central nervous system, comprising the brain and spinal cord. The condition is characterized by the immune system attacking the myelin sheath, the protective covering of nerve fibers, leading to disrupted communication within the nervous system. The course of the disease is highly variable, with symptoms ranging from mild to severely disabling, and it is a leading cause of neurological disability in young adults.

Signs and symptoms

Clinical presentation is highly heterogeneous and depends on the location of demyelinating lesions within the central nervous system. Common early symptoms include unilateral visual impairment, sensory disturbances like numbness, and electric shock sensations with neck flexion. Motor symptoms often involve muscle stiffness and weakness, while cerebellar involvement can cause tremor and gait instability. Many individuals experience significant fatigue, urinary incontinence, and problems with memory and concentration. The course often follows a relapsing and remitting pattern, where acute exacerbations are followed by periods of partial or complete recovery.

Causes and risk factors

The exact cause remains unknown but is believed to involve a complex interaction between genetic predisposition and environmental triggers. Major genetic risk is associated with the HLA-DRB1*15:01 allele. A strongly implicated environmental factor is infection with the Epstein-Barr virus, which is nearly ubiquitous in individuals with the condition. Other risk factors include low levels of vitamin D, possibly linked to reduced sun exposure at higher latitudes, as seen in populations in Northern Europe and Canada. Smoking and childhood obesity are also recognized modifiable risk factors.

Pathophysiology

The disease is defined by focal areas of inflammation and subsequent damage to the myelin sheaths produced by oligodendrocytes in the white matter. This demyelinating process is driven by an aberrant adaptive immune response, where autoreactive T cells, particularly T-helper cells, cross the blood-brain barrier. These cells, along with B cells and macrophages, orchestrate an attack that leads to sclerotic plaques or lesions. Over time, repeated episodes cause axonal damage and progressive neurodegeneration, which underlies the accumulation of permanent disability.

Diagnosis

Diagnosis is primarily clinical but relies on demonstrating dissemination of lesions in both time and space within the central nervous system, as outlined in the revised McDonald diagnostic criteria. Magnetic resonance imaging (MRI) of the brain and spinal cord is the key paraclinical tool, revealing characteristic hyperintense lesions in regions like the periventricular white matter and corpus callosum. Supportive tests include analysis of cerebrospinal fluid (CSF) for oligoclonal bands and assessment of visual evoked potentials. Differential diagnosis involves ruling out conditions such as neuromyelitis optica and neurosarcoidosis.

Management

While there is no known cure, management focuses on modifying the disease course, treating acute attacks, and managing symptoms. Disease-modifying therapies (DMTs) are the cornerstone for reducing relapse rates and delaying disability; these include injectable interferons, monoclonal antibodies like natalizumab, and oral agents such as fingolimod. Acute relapses are often treated with high-dose intravenous methylprednisolone. Symptomatic management employs physical and occupational therapy, medications for spasticity (e.g., baclofen) and neuropathic pain (e.g., gabapentin), and treatment for associated mood disorders.

Prognosis

The prognosis is highly variable and unpredictable. Most individuals are diagnosed with the relapsing-remitting form, but many eventually transition to secondary progressive disease, marked by steady neurological decline independent of relapses. A smaller proportion present with primary progressive disease from onset. Although the condition rarely directly causes death, it can reduce average life expectancy by several years. The degree of disability is often measured using the Kurtzke Expanded Disability Status Scale (EDSS), with outcomes influenced by factors like age of onset, initial symptoms, and response to DMTs.

Category:Autoimmune diseases Category:Neurological disorders