Which infectious process is most commonly cited as a medical etiology that can mimic psychiatric illness by causing altered mental status?

• A. Encephalitis
• B. Meningitis
• C. Brain abscess
• D. Sepsis

Answer: (B)

The key idea is that infections can cause delirium, making a medical illness look like a primary psychiatric disorder. Meningitis, in particular, is classically cited as a medical cause of altered mental status that can masquerade as psychiatric illness because the inflammation of the meninges often produces acute confusion, agitation, or other behavioral changes. This psychiatric‑like presentation can occur even before more classic signs (fever, neck stiffness) are evident, which is why meningitis is a critical diagnosis to consider in someone with new or worsening psychiatric symptoms.

Encephalitis can also cause altered mental status, but it more often brings additional features such as seizures or focal neurologic signs due to direct brain involvement. A brain abscess typically presents with focal neurologic deficits and progressively worsening headaches rather than a primary psychiatric picture. Sepsis can cause delirium as a result of systemic illness, but the scenario emphasizes a CNS infection that specifically mimics psychiatric illness, for which meningitis is the most commonly described example.