USMLE® Step 2 CK Question of the Day: Altered mental status

Today, we’re examining a clinical case of a 65-year-old man in the ER with an altered mental state. What are the next steps to identify the likely cause?

A 65-year-old man presents to the emergency department with confusion and lethargy over the past week. The patient has been increasingly fatigued and has lost a significant amount of weight over the past two months. Over the past several days, he has also experienced nausea, vomiting, increased thirst, and frequent urination. Additionally, he has had a persistent cough for the past three months. He has a 40-pack-year smoking history and has not seen a physician in several years. Temperature is 37.0 °C (98.6 °F), pulse is 90/min, respiratory rate is 18/min, blood pressure is 148/80 mmHg, and oxygen saturation is 94% on room air. On physical examination, the patient is disoriented to time and place and has dry mucous membranes. There are no focal neurological deficits, but generalized weakness is present. A cardiovascular exam is unremarkable. Diffuse Rhonchi are heard over the left lung field. Laboratory results are shown below.

Which of the following is the best next step in determining the cause of this patient’s altered mental status?

A. Magnetic resonance imaging (MRI) of the brain

B. Abdominal ultrasound

C. Serum protein electrophoresis

D. Chest radiograph

E. Lumbar puncture

Scroll down for the correct answer!

The correct answer to today’s USMLE® Step 2 Question is…

D. Chest radiograph

Correct: See Main Explanation.

Incorrect Answer Explanations

A. Magnetic resonance imaging (MRI) of the brain

Incorrect: While MRI of the brain can detect central nervous system causes of altered mental status and may be used for staging if cancer is diagnosed, the presence of hypercalcemia along with his smoking history and lung findings makes lung malignancy more likely.

B. Abdominal ultrasound

Incorrect: An abdominal ultrasound is unlikely to identify the primary cause of altered mental status and hypercalcemia in this patient who most likely has lung cancer.

C. Serum protein electrophoresis

Incorrect: Serum protein electrophoresis is used to diagnose multiple myeloma and can be part of the workup for hypercalcemia. This patient’s history and presentation are more suggestive of hypercalcemia due to lung cancer; therefore, a chest radiograph should be performed next to confirm the diagnosis.

E. Lumbar puncture

Incorrect: A lumbar puncture is typically performed to diagnose neurologic infections or central nervous system pathologies. It will not help diagnose the underlying cause of this patient’s altered mental status, hypercalcemia, and lung findings.

Main Explanation

This patient presents with altered mental status (AMS) likely due to hypercalcemia. The recent symptoms of nausea, vomiting, increased thirst, and frequent urination are consistent with hypercalcemia. Given the significant weight loss, chronic cough, heavy smoking history, and lung exam findings, hypercalcemia is most likely due to an underlying malignancy, such as lung cancer in this patient. A chest radiograph is the most appropriate next step to evaluate lung mass, which could be the cause of hypercalcemia and altered mental status.

Determining the etiology of AMS requires targeted diagnostic tests based on clinical suspicion. For metabolic causes, such as hyperglycemia or uremia, basic blood tests like a basic metabolic panel are essential. Infectious causes (e.g., meningitis) may require a lumbar puncture to analyze cerebrospinal fluid, while imaging studies such as computed tomography (CT) or magnetic resonance imaging (MRI) scans of the brain are necessary to identify structural causes such as stroke or tumors. Specific imaging, like a chest radiograph or abdominal ultrasound, may be needed to identify underlying malignancies or other systemic causes of AMS. Toxicologic screening should be performed when drug overdose or poisoning is suspected. 

Major Takeaway 

In patients presenting with altered mental status, identifying the underlying cause often requires targeted diagnostic tests, such as serum laboratory studies to assess for metabolic imbalances, imaging studies for structural abnormalities or underlying malignances or toxicological screening for suspected poisoning or overdoses.  

Want to learn more about this topic?

Watch the Osmosis video: Approach to altered mental status: Clinical Sciences

References 

• LaHue SC, Douglas VC. Approach to Altered Mental Status and Inpatient Delirium. Neurol Clin. 2022;40(1):45-57. doi: 10.1016/j.ncl.2021.08.004
• Selvadurai C. Altered Mental Statu. In: Leppert BC, ed. Netter’s Integrated Review of Medicine. Elsevier, Inc.; 2021:53-58.
• Veauthier B, Hornecker JR, Thrasher T. Recent-Onset Altered Mental Status: Evaluation and Management. Am Fam Physician. 2021;104(5):461-470.

Want more USMLE® Step 2 CK practice questions? Try Osmosis from Elsevier today! Access your free trial and discover why millions of current and future clinicians and caregivers love learning with us.