Differential Diagnosis for Altered Mental Status

The patient's presentation with subacute onset of altered mental status, history of substance use, and recent head trauma requires a comprehensive differential diagnosis. The following categories organize potential diagnoses based on likelihood and urgency:

• Single Most Likely Diagnosis

  • Wernicke's Encephalopathy: Given the patient's history of alcohol use disorder and the subacute onset of altered mental status, Wernicke's encephalopathy is a strong consideration. The condition is characterized by confusion, ataxia, and ophthalmoplegia, often precipitated by thiamine deficiency in the context of chronic alcohol abuse. The patient's initial episode of lethargy and difficulty arousing could be an early manifestation, and the subsequent bizarre behavior following head trauma might be a progression of the condition or a separate entity.

• Other Likely Diagnoses

  • Chronic Subdural Hematoma: The patient's recent fall and head trauma could have resulted in a chronic subdural hematoma, which might present with altered mental status, especially in the context of a subacute onset. The initial headache followed by bizarre behavior could be indicative of increasing intracranial pressure or mass effect.
  • Substance-Induced Psychosis: Given the patient's history of recreational opioid use, substance-induced psychosis is a possibility. However, the subacute onset and the fact that the patient returned to baseline before the onset of bizarre behavior make this less likely.
  • Traumatic Brain Injury (TBI) Sequelae: The head trauma could have resulted in a TBI, with the subsequent behavioral changes being part of the post-concussive syndrome or a more severe brain injury.

• Do Not Miss Diagnoses

  • Meningitis or Encephalitis: Infections such as meningitis or encephalitis can present with altered mental status and require urgent diagnosis and treatment. Although less likely given the subacute onset, these conditions are critical not to miss due to their high morbidity and mortality.
  • Subarachnoid Hemorrhage: Although the patient's presentation does not classically suggest a subarachnoid hemorrhage (e.g., sudden, severe headache), any form of head trauma increases the risk, and missing this diagnosis could be fatal.
  • Brain Abscess: A brain abscess could present with altered mental status and has a high potential for morbidity and mortality if not promptly treated.

• Rare Diagnoses

  • Hashimoto's Encephalopathy: A rare condition associated with autoimmune thyroiditis, characterized by altered mental status, which could be considered in the differential diagnosis given the patient's presentation.
  • Creutzfeldt-Jakob Disease: A prion disease that presents with rapidly progressive dementia and altered mental status. Although very rare, it is worth considering in cases where the diagnosis remains elusive.
  • Reversible Posterior Leukoencephalopathy Syndrome (PRES): Typically associated with hypertension, eclampsia, or certain medications, PRES could present with altered mental status and seizures, although it is less likely given the patient's history and presentation.