Dementia l: Introduction

Dementia is an acquired, progressive syndrome characterized by a decline in multiple cognitive domains severe enough to impair daily functioning and reduce independence. Although memory loss is a central feature, the diagnosis requires additional deficits involving language, executive function, visuospatial skills, judgment, calculation, or abstract reasoning. These cognitive impairments reflect underlying neurodegenerative or vascular processes that gradually disrupt neuronal networks essential for higher cortical function.

Alzheimer’s Disease

Alzheimer’s disease is the most common cause of dementia and is defined by two hallmark pathological features. Beta-amyloid plaques form when amyloid-β peptides aggregate extracellularly and accumulate between neurons, interfering with synaptic signaling and triggering local inflammatory responses. Neurofibrillary tangles, composed of hyperphosphorylated tau protein, develop intracellularly. When tau becomes excessively phosphorylated, it detaches from microtubules, destabilizing the cytoskeleton and impairing axonal transport. These combined processes lead to synaptic dysfunction and progressive neuronal loss. Degeneration begins prominently in the hippocampus and medial temporal lobes—regions essential for forming new memories—and later spreads to association cortices, contributing to worsening cognitive impairment.

Vascular Dementia

Vascular dementia arises from compromised cerebral perfusion and oxygenation. Ischemic injury may occur through large-vessel infarcts, multiple small-vessel lacunar strokes, or chronic microvascular disease. Each of these processes disrupts cortical and subcortical pathways necessary for cognition. The resulting deficits often appear stepwise, corresponding to successive vascular events, and may include impaired attention, slowed processing speed, and executive dysfunction.

Dementia frequently involves mixed pathology, with both neurodegenerative and vascular contributions. Early recognition of symptoms and underlying mechanisms is essential for appropriate management, risk factor modification, and supportive care planning.