Secondary Spinal Cord Injury llI: Pathophysiology

Vascular damage reduces blood flow, causing ischemia and mitochondrial dysfunction within minutes. ATP depletion leads to ion pump failure, membrane depolarization, sodium influx, and potassium efflux. Intracellular water accumulates, resulting in cellular swelling and progressive tissue injury that worsens over hours to weeks.

Damaged neurons release excess glutamate, overstimulating NMDA receptors and allowing calcium to surge into cells. Elevated intracellular calcium activates destructive enzymes, worsens mitochondrial dysfunction, and promotes progressive neuronal damage. This excitotoxic cascade significantly accelerates cellular injury beyond the initial trauma.

Microglia activate rapidly, and immune cells infiltrate through damaged vessels, releasing cytokines, chemokines, and reactive oxygen species. These inflammatory mediators increase blood-spinal cord barrier permeability, leading to vasogenic edema and extracellular fluid accumulation. Rising tissue pressure further reduces perfusion, creating a self-amplifying cycle of injury.

Oligodendrocytes are especially susceptible to oxidative stress and delayed programmed cell death triggered by sustained hypoxia and inflammation. Their loss results in demyelination of axons, slowing nerve conduction velocity. This demyelination contributes to persistent functional deficits and expanding lesion size beyond the original insult.

Sustained hypoxia and inflammation generate oxidative stress, which damages lipids, proteins, and DNA in neurons and glial cells. This cellular damage triggers delayed programmed cell death, expanding the lesion and worsening neurological deficits. Reactive oxygen species from infiltrating immune cells intensify this destructive process.

In later stages, reactive astrocytes proliferate and form a glial scar that helps contain the injury and limit further damage. However, the glial scar also inhibits axonal regeneration, contributing to long-term functional limitations. This dual role reflects the complex balance between neuroprotection and neuroplasticity.

Secondary injury mechanisms progressively enlarge the area of damage through ischemia, excitotoxicity, inflammation, and demyelination. Patients experience worsening motor and sensory function as the lesion expands and neural conduction becomes impaired. This expansion occurs over hours to weeks, distinguishing secondary injury from the initial traumatic insult.