Etiology
The most common causes of AMS are cerebrovascular, traumatic, neurologic, cardiac, psychiatric, metabolic, pulmonary, endocrinologic, infectious, gastrointestinal, or exogenous. They either directly affect the central nervous system (CNS) or have a secondary neurologic impact.[1] An observational study of people ages 65 years and older presenting with AMS (≤1 week) to four emergency departments in Turkey found that the most common etiology was infection (39.5%), followed by neurologic disease (36.5%).[4] Almost any stress can present as AMS in infants, older people, or debilitated patients.
Cerebrovascular
By directly affecting the CNS, the following cerebrovascular causes can alter mental status: stroke, subdural hematoma, epidural hematoma, and subarachnoid hemorrhage.
Traumatic
Head injuries (e.g., concussions, traumatic brain injuries) are common neurologic conditions that alter mental status.[7] Hip tenderness might suggest occult hip fracture, a frequently missed trigger for delirium in frail older patients, particularly if they are bed-bound.[8][9][10]
Neurologic
Dementia, delirium, seizures (status epilepticus or postictal states), tumors, hypertensive encephalopathy, nonconvulsive status epilepticus, and Wernicke encephalopathy may all alter mental state.
Cardiac and pulmonary
Systemic diseases that have neurologic consequences include cardiac disorders such as myocardial infarction, congestive heart failure, and arrhythmias. Pulmonary embolism, hypoxia, and carbon monoxide poisoning are other diagnoses that may result in AMS.
Psychiatric
Acute psychoses can alter neurologic function. Patients with acute psychosis typically show 1 or more of the following symptoms or signs: delusions, hallucinations, disorganized speech, or grossly disorganized or catatonic behavior lasting >24 hours but <30 days. Depression (including catatonia) and bipolar mania may also present as AMS.
Metabolic
The following metabolic conditions/imbalances can have neurologic consequences: dehydration; hepatic encephalopathy; uremia; hypothermia and hyperthermia; hypercapnia; hypo/hypernatremia; hypo/hyperglycemia; and hyper/hypocalcemia. Mental status changes in patients with ketoacidosis should alert clinicians to other potential causes, such as toxic ingestion, hypoglycemia, alcohol-withdrawal seizures, postictal state, or unrecognized head injury.
Endocrinologic
Adrenal insufficiency, thyrotoxicosis, myxedema coma, and pituitary apoplexy can result in AMS.
Infectious
Meningitis, acute systemic infections (e.g., pneumonia, urinary tract infection, skin/soft-tissue infections, cholecystitis), encephalitis, neurosyphilis, and brain abscesses can alter mental status.
Gastrointestinal
This group (notwithstanding surgical conditions in other anatomic locations) includes mesenteric ischemia, diverticulitis, appendicitis, and constipation. The latter can be associated with hypercalcemia or myxedema coma.
Exogenous
Common exogenous toxins that can cause AMS include medications such as anticholinergics, sympathomimetics, antihistamines, antiemetics, opioids, antiparkinsonian medications, and antispasmodics.
Withdrawal from alcohol and sedatives can also precipitate changes in mental function.
Illicit drugs such as opiates, amphetamines, cocaine, and hallucinogens are frequently implicated.
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