What is the underlying cause of this patient’s symptoms? A 32-year-old HIV-positive man with a recent CD4+ cell count of 84/mm³ and a 3-week history of worsening headaches is brought to the emergency department by ambulance because of acute mental status changes. Upon arrival he is noted to have papilledema, a third cranial nerve palsy, and a rigid neck that cannot be flexed or extended. He subsequently dies from an overwhelming infection involving his nervous system. An autopsy specimen of the patient’s brain is shown in the image.

Mycobacterial meningitis

21. The correct answer is D. This patient suffered from tuberculous meningitis, which is demonstrated by the characteristic acid-fast bacilli present in the patients brain tissue. Immunocompromised patients are at risk for developing tuberculous meningitis, which occurs after the central nervous system (CNS) is seeded with mycobacteria that subsequently produce a thick, gelatinous exudate. This exudate typically collects in the basilar region of the CNS and can cause cranial nerve dysfunction (com- monly cranial nerves III, VI, and VII) as well as obstruction of the basilar cisterns, resulting in obstructive hydrocephalus. The presence of cranial nerve involvement and/or obstructive hydrocephalus portends a poor prognosis. Answer A is incorrect. Although bacterial meningitis may occur in immunocompromised patients, this tissue section is not consistent with a bacterial infection. Streptococcus pneumoniae and Neisseria meningitidis, the two most common causes of bacterial meningitis, are cocci-shaped organisms. Answer B is incorrect. Although fungal meningitis may occur in immunocompromised patients, this tissue section is not consistent with a fungal infection. Answer C is incorrect. Although herpes encephalitis may occur in immunocompromised patients, this tissue section is not consistent with a viral herpetic infection. Answer E is incorrect. Although viral meningitis may occur in immunocompromised patients, this tissue section is not consistent with a viral infection.