Delirium is a temporary neurological disorder characterized by rapid onset of cognitive impairment and disturbance in consciousness. It can cause confusion, disorientation, and a distorted perception of reality. Delirium can have severe and long-lasting consequences.
Delirium is not a disease itself but rather a symptom of an underlying medical condition or an adverse reaction to a medication. There are several common causes. Infections can precipitate delirium, more so in the elderly. Especially in excessive doses, certain drugs can cause it, particularly sedatives, antipsychotics, and medications with anticholinergic properties. Conversely, abrupt cessation of drug or alcohol use can cause withdrawal delirium, also known as delirium tremens. Another cause of delirium is metabolic disturbance, such from electrolyte imbalances, dehydration, and organ dysfunction, since these can all disrupt brain function. Trauma and surgery can trigger delirium due to stress response and anesthesia. Neurological conditions like strokes, seizures, and brain tumors that affect brain areas responsible for cognitive function can also cause it. Certain psychiatric conditions, such as bipolar disorder and schizophrenia may increase risk of delirium during episodes of extreme mood disturbance. Finally, environmental factors can trigger delirium. Specifically, hospitalization, particularly in the ICU, with constant light, noise, mechanical ventilation, sleep deprivation, sedation, and unfamiliar surroundings, can contribute to what is referred to as ICU delirium. Some individuals may be more vulnerable to developing delirium due to preexisting neurological conditions, such as dementia. In these cases, the underlying brain abnormalities may make them more susceptible to it when faced with stressors like infection or surgery.
Symptoms of delirium are diverse and vary from person to person. However, there are a few hallmark features. Fluctuating alertness, in which individuals alternate between extreme alertness and confusion. Impaired attention, in which they are easily distracted from tasks or conversations. Disorganized thinking, in which it is hard to organize ideas, and potentially also fragmented speech. There may be vivid sensory hallucinations, or the person may hold false beliefs. The person may have an altered sleep-wake cycle, leading to insomnia or daytime sleepiness. Some individuals become agitated, aggressive, or restless, while others become lethargic and withdrawn.
Delirium is closely linked to disturbances in neurotransmitter systems. The changes in neurotransmitter levels during delirium can vary depending on the underlying cause and individual factors, but several key neurotransmitters are often involved.
Decreased levels of acetylcholine are commonly observed in delirium. This neurotransmitter is involved in various cognitive functions, including memory, attention, and alertness. High levels of dopamine are associated with symptoms such as agitation, hallucinations, and delusions, which are often observed in hyperactive delirium. Conversely, low dopamine levels can lead to apathy and decreased alertness seen in hypoactive delirium. Serotonin is involved in mood regulation and sleep-wake cycles. Alterations in serotonin levels can contribute to mood disturbances and disruptions in sleep patterns. Norepinephrine is involved in the body's stress response and plays a role in maintaining alertness and attention. Abnormal levels of this neurotransmitter can lead to symptoms such as restlessness and increased heart rate. The inhibitory neurotransmitter GABA helps regulate brain activity. Changes in its levels may contribute to altered consciousness and sedation.
The hypothalamic-pituitary-adrenal axis and other hormonal systems also come into play. Stress-induced activation of the HPA axis leads to increased cortisol production. Elevated cortisol levels are thought to contribute to cognitive impairment and delusional thinking.
Disruptions in the sleep-wake cycle are common in delirium. Melatonin, a hormone regulating circadian rhythms, is often altered in delirious patients, and this can exacerbate sleep disturbances and further compromise cognitive function.
The frontal cortex, responsible for executive functions, attention, and decision-making, is particularly vulnerable in delirium. Disruptions in this region can lead to impaired judgment and reasoning. Delirium is associated with altered patterns of brain connectivity, and functional imaging studies have shown that there can be disruptions in the normal communication between different regions of the brain. This disruption can explain the fluctuating nature of symptoms seen in delirium, as different brain networks become engaged or disengaged. Structural brain changes, such as white matter lesions, can disrupt neuronal signaling and contribute to cognitive impairment. Blood-Brain Barrier integrity may also be compromised during delirium.
22 июл 2024
