Multiple Sclerosis (MS) is a chronic disease of the central nervous system (CNS) involving the brain and spinal cord. It is an autoimmune condition where the immune system attacks the myelin sheath, the protective covering around nerve fibers. This damage disrupts communication between the brain and the rest of the body. While MS is a progressive and disabling disease, it is rarely the direct cause of death. Mortality in individuals with advanced MS occurs due to secondary complications arising from long-term disability and immobility.
Multiple Sclerosis and Organ System Function
The pathology of MS involves inflammatory demyelination and neurodegeneration. Myelin destruction slows electrical signals along the nerves, causing characteristic symptoms like weakness, impaired coordination, and sensory loss. Over time, this damage leads to the irreversible loss of axons and brain tissue atrophy, driving permanent neurological disability.
MS primarily targets the CNS; it does not cause the failure of peripheral organs like the heart, liver, or kidneys. Instead, it compromises the body’s ability to control these functions by damaging communication pathways. For example, the brain stem regulates involuntary actions such as breathing, heart rate, and swallowing. Severe damage in this region can directly impair the muscles responsible for these life-sustaining functions.
As the disease progresses, muscle weakness and spasticity develop, leading to loss of mobility and independence. This severe disability causes fatal complications. Weakness in the chest and diaphragm muscles reduces lung capacity and the ability to cough effectively, setting the stage for respiratory illness. Damage to the nerves controlling the throat muscles results in dysphagia, or difficulty swallowing, which contributes to terminal complications.
Common Terminal Complications
The cause of death in advanced MS is almost always a secondary condition resulting from accumulated disability. Respiratory issues are the most common terminal event. Aspiration pneumonia occurs when a person with dysphagia inhales food or liquid into the lungs. This foreign material introduces bacteria, leading to a severe lung infection that the weakened respiratory system struggles to clear.
Respiratory failure is a major risk, resulting from the progressive weakening of breathing muscles. The inability to expand the lungs fully causes shallow breathing and chronic respiratory insufficiency. This makes the person highly susceptible to infections like influenza or bacterial pneumonia, a risk compounded by general immobility.
Infections originating elsewhere can escalate rapidly to life-threatening sepsis. Severe urinary tract infections (UTIs) are common because MS often causes bladder dysfunction, leading to incomplete emptying or requiring catheterization. Prolonged immobility also leads to pressure ulcers (bedsores), which can become deeply infected and cause systemic sepsis if bacteria enters the bloodstream.
Vascular complications are linked directly to prolonged physical inactivity. Immobility increases the risk of deep vein thrombosis (DVT), or blood clots that form in the legs. If a clot fragment travels to the lungs, it causes a pulmonary embolism (PE), a sudden blockage of a lung artery that can be rapidly fatal.
Life Expectancy and Disease Modifying Therapies
Life expectancy for people with Multiple Sclerosis has improved due to advances in supportive care and treatment. Life expectancy is typically reduced by about five to ten years compared to the general population. Many individuals with a less aggressive disease course or who respond well to treatment live a full or near-full lifespan.
The advent of Disease Modifying Therapies (DMTs) has played a role in this improved outlook. DMTs target the inflammatory and autoimmune processes of MS, reducing the frequency of relapses and slowing disability accumulation. Using DMTs has been shown to reduce mortality risk and improve long-term survival.
Proactive management of symptoms and complications is important in mitigating mortality risk. This includes preventing infections through diligent bladder and bowel care, ensuring adequate nutrition, and engaging in physical therapy to maintain mobility. Managing the secondary conditions that arise from advanced disability reduces the risk of a life-limiting terminal event.