Clinical meaning
Delirium is an acute, fluctuating disturbance in attention, awareness, and cognition that develops over hours to days and represents a medical emergency. Unlike dementia, delirium is typically reversible when the underlying cause is identified and treated. The pathophysiology involves widespread disruption of neurotransmitter signaling, particularly an imbalance between acetylcholine (which decreases) and dopamine (which increases) in the brain. This neurochemical disruption impairs the reticular activating system, which controls arousal and attention, and disrupts cortical-subcortical connectivity. The aging brain is particularly vulnerable to delirium because of age-related reductions in cerebral blood flow, decreased cholinergic reserve, increased blood-brain barrier permeability, and reduced neuronal density. These changes mean that even minor physiological insults such as urinary tract infections, constipation, dehydration, or medication changes can trigger delirium in elderly patients. Inflammatory cytokines released during acute illness (interleukin-1, interleukin-6, tumor necrosis factor-alpha) cross the compromised blood-brain barrier and directly impair neurotransmission. Oxidative stress and neuroinflammation further damage vulnerable neurons. Delirium exists in three motor subtypes: hyperactive (agitation, hallucinations, restlessness), hypoactive (lethargy, reduced responsiveness, withdrawal), and mixed (alternating between the two). Hypoactive delirium is the most...