What are the possible causes of altered mental status?

Causes of Altered Mental Status

Altered mental status results from a wide range of medical conditions that can be systematically categorized into neurological, toxicological/pharmacological, infectious, metabolic/endocrine, systemic, traumatic, and psychiatric etiologies, with neurological causes being most common (28-35%), followed by toxicological causes (21-23%). 1, 2, 3

Primary Etiologic Categories

Neurological Causes (Most Common: 28-35%)

• Ischemic stroke and cerebrovascular disease are leading causes, with stroke accounting for a significant proportion of deaths in AMS patients 1, 4
• Intracranial hemorrhage (subdural hematoma, subarachnoid hemorrhage) particularly in patients on anticoagulation or with unrecognized trauma 1, 4
• Seizure disorders including status epilepticus and nonconvulsive seizures, which are frequently missed without EEG 1, 5
• Intracranial mass effect from tumors, metastases, or globally elevated intracranial pressure 1, 4
• Central nervous system infections (meningitis, encephalitis) typically presenting with fever and altered consciousness 1, 5
• Dementia disorders and transient ischemic attacks 1
• Hydrocephalus 1

Toxicological and Pharmacological Causes (21-23%)

• Polypharmacy is a major contributor, especially in elderly patients 4, 5
• Anticholinergic medications (antihistamines, tricyclic antidepressants) 4, 5
• Sedatives, benzodiazepines, and narcotics 1, 4
• Drug intoxication from various substances 1, 2
• Alcohol or drug withdrawal states which require immediate recognition and treatment 5, 6

Infectious Causes (9-10%)

• Urinary tract infection is the most common infectious precipitant in elderly patients 1, 4
• Pneumonia and other respiratory infections 4, 6
• Sepsis from any source can precipitate delirium with psychotic features 5, 6

Metabolic and Endocrine Causes (5-8%)

• Hypoglycemia and hyperglycemia require immediate point-of-care glucose testing as among the most common reversible causes 4, 6
• Severe electrolyte abnormalities (hyponatremia, hypernatremia, hypercalcemia) can rapidly cause altered consciousness 4, 6
• Thyroid disorders (hypothyroidism, thyrotoxicosis) should be screened in elderly patients with new psychiatric symptoms 4, 6
• Adrenal insufficiency 4
• Wernicke encephalopathy from thiamine deficiency 1

Systemic and Organ Dysfunction (14-15%)

• Hypoxia from any respiratory cause must be assessed immediately with pulse oximetry 4, 6
• Hepatic encephalopathy in patients with cirrhosis 6
• Renal failure and uremia 2, 3
• Acute myocardial infarction 1
• Hypothermia can precipitate delirium 4

Traumatic Causes (2-14%)

• Traumatic brain injury with or without obvious external signs of trauma 1, 5, 3
• Chronic subdural hematoma from unrecognized trauma, especially in anticoagulated patients 1, 4

Psychiatric Causes (3-14%)

• New-onset psychosis 1, 5
• Severe depression with psychomotor retardation 5
• Catatonia 5

Critical Diagnostic Distinction: Delirium

Delirium is a medical emergency that accounts for 7-35% of ED presentations with AMS and carries twice the mortality when missed. 1, 4

Key Features of Delirium:

• Inattention as cardinal feature with fluctuating consciousness over the course of the day 1, 4
• Acute onset over hours to days, not insidious progression 4, 5
• Infection is the most common precipitating factor, particularly urinary tract infections in elderly patients 1, 4
• Multifactorial etiology including surgery, ICU stay, environmental factors, restraints, stress, pain, and sleep deprivation 1

Prognostic Information

• Overall mortality in AMS patients is 8.1%, significantly higher in elderly patients (10.8% vs 6.9% in younger patients) 1, 2
• Mortality doubles when delirium diagnosis is missed, emphasizing the critical need for early recognition 1, 4
• The cause remains undiagnosed in >5% of cases despite comprehensive evaluation 1

Common Pitfalls to Avoid

• Do not attribute AMS solely to psychiatric causes without adequate medical workup, as life-threatening conditions may be missed 6, 3
• Do not overlook withdrawal states, which require immediate benzodiazepine treatment to prevent seizures 5
• Do not delay empiric treatment while awaiting diagnostic results in potentially life-threatening conditions 6
• Do not assume normal neurological examination excludes stroke, as small lacunar infarcts can present without focal deficits 4
• Do not rely on ammonia levels alone to diagnose hepatic encephalopathy in cirrhotic patients 6