What is the next step in diagnosing an 8-year-old woman with a history of alcohol use disorder (AUD) and recent opioid use, presenting with subacute altered mental status and bizarre behavior following a head injury?

Diagnostic Approach for Altered Mental Status in a Patient with Substance Use History and Head Trauma

The next step in diagnosis for this patient should be a non-contrast head CT scan to evaluate for traumatic brain injury, intracranial hemorrhage, or other structural abnormalities. 1

Clinical Reasoning

This 8-year-old female patient presents with several concerning features that require immediate neuroimaging:

1. Recent head trauma - The patient fell and hit her head 3 weeks ago, followed by progressive bizarre behavior
2. History of substance use - Recent use of multiple opioids (morphine, oxycodone, heroin)
3. Alcohol use disorder - Underlying condition that increases risk of traumatic injury
4. Subacute onset of altered mental status - Gradual worsening over a month

Why Head CT is the Priority

• The American College of Radiology recommends head CT without contrast as the first-line neuroimaging test for patients with acute mental status changes who have increased risk for intracranial bleeding (anticoagulant use, coagulopathy), history of head trauma, or clinical suspicion for intracranial mass or infection 1, 2
• The temporal relationship between the head injury and onset of behavioral changes strongly suggests a traumatic etiology such as subdural hematoma, epidural hematoma, or traumatic brain injury
• The American Academy of Pediatrics guidelines state that central nervous system abnormalities such as intracranial hemorrhage can present primarily with psychiatric symptoms 1

Differential Diagnosis

The patient's presentation requires consideration of several potential etiologies:

• Traumatic brain injury - Subdural hematoma, epidural hematoma, cerebral contusion
• Drug-related neurotoxicity - From recent opioid use or alcohol
• Metabolic encephalopathy - Particularly related to alcohol use disorder
• Infectious process - Meningitis, encephalitis, brain abscess
• Seizure disorder - Post-traumatic epilepsy

Additional Diagnostic Steps After Head CT

After obtaining the head CT, these additional diagnostic steps should be considered:

1. Laboratory studies:

   • Complete blood count
   • Comprehensive metabolic panel (electrolytes, liver function, kidney function)
   • Toxicology screen for drugs and alcohol
   • Ammonia level (given alcohol use disorder and potential for hepatic encephalopathy) 1

2. If CT is negative but clinical suspicion remains high:

   • Brain MRI - More sensitive for detecting subtle abnormalities, particularly in the temporal and frontal lobes 2
   • EEG - To evaluate for seizure activity or encephalopathy 2
   • Lumbar puncture - If infection is suspected 1

Common Pitfalls to Avoid

1. Attributing symptoms solely to psychiatric causes - The temporal relationship to head trauma strongly suggests an organic etiology
2. Overlooking alcohol withdrawal - Can cause delirium, hallucinations, and bizarre behavior
3. Missing drug interactions - Alcohol and opioids have significant pharmacodynamic interactions that can cause prolonged neurotoxicity 3
4. Delaying neuroimaging - Waiting for laboratory results before obtaining neuroimaging could delay diagnosis of a life-threatening condition

Conclusion

Given this patient's presentation with progressive altered mental status following head trauma, in the context of substance use and alcohol use disorder, a non-contrast head CT scan is the most appropriate next diagnostic step. This approach aligns with current guidelines and addresses the most urgent potential cause of her symptoms - a structural brain abnormality requiring urgent intervention.