Altered Mental Status Differential Diagnosis Mnemonic – USMLE Step 2 CS

Altered Mental Status Differential Diagnosis Mnemonic - USMLE Step 2 CS -
Altered Mental Status Differential Diagnosis Mnemonic

Altered Mental Status Differential Diagnosis Mnemonic for USMLE Step 2 CS

Altered mental status (AMS) is a common chief complaint among older patients presenting to the emergency department. Despite the frequency of this complaint, the term “altered mental status” is vague and has several synonyms such as “confusion”, “not acting right”, “altered or inappropriate behavior”, “generalized weakness”, “lethargy”, “agitation”, “psychosis”, “disorientation”, “inattention”, and “hallucination”.

It is very important to understand that Altered mental status is a symptom and not a disease. Causes range from easily reversible (hypoglycemia) to permanent (intracranial hemorrhage) and from the relatively benign (alcohol intoxication) to life threatening (meningitis or encephalitis).

The differential diagnosis for Altered Mental Status is extensive. Developing a structured and systematic approach to these cases will help you develop and streamline the diagnostic workup and management of these patients with AMS.

Acute changes in mental status are more concerning and are usually secondary to delirium, stupor, and coma. These forms of acute brain dysfunction are commonly precipitated by an underlying medical illness that can be potentially life-threatening and are associated with a multitude of adverse outcomes. Though stupor and coma are easily identifiable, the clinical presentation of delirium can be subtle and is often missed without actively screening for it.

For patients with acute brain dysfunction, the ED evaluation should focus on searching for the underlying etiology. Infection is one of the most common precipitants of delirium, but multiple etiologies may exist concurrently.
Altered Mental Status Differential Diagnosis Mnemonic

Altered Mental Status Differential Diagnosis Mnemonic

Key Physical Exam for Altered Mental Status:

NOTE: Make sure to wash your hands or wear gloves before you start physical examination. Make sure to ask for permission before you start each physical exam. Make sure to use proper draping (don’t forget to tie back patient’s gown). Make sure to explain each physical examination in layman’s term to your patient. Do NOT repeat painful maneuvers.

Vital signs: 

  • Does the patient have a fever?
  • Is the patient bradycardic or tacycardic? bradypneic or tachypneic? hypotensive or severely hypertensive?

Neurologic exam:

  • Make sure your exam includes DTR’s, CN2-12, motor, sensory, gait
  • Is the patient alert and oriented to time, person and place?
  • How difficult is it to keep the patient awake?
  • Content of thought and speech
  • Can the patient stay focused?
  • Does the patient keep asking the same questions over and over (perseveration)?
  • Is the patient reacting to internal stimuli?
  • Glasgow Coma Scale (GCS score)
  • AVPU scale (A=alert, V=responds to verbal stimuli, P=responds to painful stimuli, U=unresponsive).

Cardiovascular exam:

  • Are there arrhythmias (a-fib) that predispose to embolic strokes?
  • Is there a murmur? endocarditis?
  • Is there evidence of good peripheral circulation?
  • Are there pulmonary findings that indicate pneumonia (sepsis) or pulmonary edema (hypoxia)?
  • Are there bruits over the carotid arteries?

Abdominal exam:

  • Is there ascites, caput medusa, spider angiomata or other signs of portal hypertension? (hepatic encephalopathy)?
  • Is the abdomen tender (appendicitis, intussusception, abdominal sepsis source including cholangitis, mesenteric ischemia)? Remember that elderly patients may not always mount leukocytosis or fever.

Genitourinary and rectal exam:

  • Is the patient making urine (uremic encephalopathy)? Consider POCUS to evaluate the bladder and kidneys
  • Are there signs or urinary, vaginal, prostatic or perineal infection?
  • Is there melena or blood in the stool? Uremia and hyperammonemia may occur secondary to upper GI bleed.

Skin, extremity, musculoskeletal exam:

  • Are there petechiae (meningococcemia, thrombocytopenia)?
  • Is there a dialysis graft (uremic encephalopathy, intracranial hemorrhage due to dysfunctional platelets)?
  • Are there track marks from injection drug abuse?
  • Are there transdermal drug patches?
  • Is the skin jaundiced (hepatic encephalopathy)?
  • Is there nuchal rigidity or meningismus (CNS infection, subarachnoid hemorrhage)?
  • Are there signs of trauma (raccoon’s eyes, Battle’s sign, hemotympanum)?
  • Are there infectious sources noted (decubitus ulcers, cellulitis, abscesses)?
  • Are there masses or lymphadenopathy that might indicate cancer (paraneoplastic syndromes)?

History and physical exam findings are usually enough to help you categorize the change in mental status as delirium, dementia or psychosis. Further testing should be ordered as below to help narrow or confirm the differential diagnosis within each of these categories of AMS.

Altered Mental Status Differential Diagnosis Mnemonic

Differential Diagnosis:

Altered Mental Status Differential Diagnosis mnemonic - MOVE STUPID mnemonic - Causes of Altered Mental Status -

Altered Mental Status Differential Diagnosis Mnemonic

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Primary CNS/Structural causes: Tumors:
    – Primary
    – Metastatic Hemorrhage:
    – Spontaneous
    – Traumatic Edema:
    – HTN encephalopathy
    – Obstructive hydrocephalus
    – Tumor 

    – Post-ictal state
    – Todd’s paralysis


    – Degenerative
    – Multi-infarct

Metabolic/Autoregulatory causes: Hypoglycemia/hyperglycemia
Pharmacologic/Toxic causes: Medication effects:
    – Hypertension
    – Steroids
    – Sedatives
    – Opiates
    – Sleep aids
    – Anticholinergics
    – Antiepileptics
    – Polypharmacy Alcohols:
    – Ethanol (ETOH)
    – Methanol/ethylene glyco Illicit drugs Withdrawal:
    – Alcohol
    – Benzodiazepine
    – Opiate
Infectious causes: Primary CNS:
    – Meningitis
    – Encephalitis
    – Abscesses Other infection:
    – UTI
    – Pneumonia
    – Skin/decubitus ulcer
    – Intra-abdominal
    – Viral syndrome
Other causes: Shock:
    – Cardiogenic
    – Hypovolemic
    – Hemorrhagic
    – Septic
    – Neurogenic Psychiatric disorder:
    – Acute
    – Chronic Complicated migraine 

Sundowning/ICU delirium

Altered Mental Status Differential Diagnosis Mnemonic

Work-up for Altered Mental Status:

  • Fingerstick Blood Sugar*: Hypoglycemia is common, deadly and reversible cause of altered mental status that should be assessed in all altered patients.
  • Electrolytes: to rule out electrolyte abnormalities.
  • BUN/Creatinine: to rule out uremia and upper GI bleed.
  • Serum bicarbonate in the basic metabolic panel helps assess degree of acidosis and may clue to a broad differential diagnosis. 
  • Arterial or Venous Blood Gases
  • Cardiac enzymes to rule out myocardial infarction.
  • Serum Ammonia level
  • Urinalysis: to rule out urinary tract infection.
  • Urine toxicology: screen for benzodiazepines, opioids, barbiturates and alcohol toxicity.
  • CBC with differential
  • Serum lactic acid if meets systemic immune response syndrome (marker for severe sepsis or septic shock)
  • Urinalysis and culture
  • Blood culture
  • Chest X-ray 
  • Vitamin B12 level
  • Thyroid function tests
  • Electrocardiogram (ECG): to rule out myocardial infarction. Also to check for QTc prolongation since certain medications such as TCA can prolong QTc and others like lithium cause other arrhythmias.
  • CT of the head: to rule out intracranial hemorrhage or masses.
  • MRI of the brain: to rule out ischemic stroke.
  • Lumbar puncture for CSF analysis [NOTE: always obtain a CT scan of the head prior to lumbar puncture if you suspect an increased intracranial pressure (ICP)]
  • Electroencephalogram (EEG): if you suspect seizure disorder.


Reference: [1][2][3][3][5]

Altered Mental Status Differential Diagnosis Mnemonic

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Altered Mental Status Differential Diagnosis Mnemonic

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