HIV/AIDS overview

In our #AMreport @WCHospital, given that today is World AIDS day we reviewed certain opportunistic infections, focusing on a case of cryptococcal meningitis. A young man presented with a 2-4 week history of confusion and fever. No focal deficits were identified on exam and neuro-imaging was normal. Further investigations done with an lumbar puncture revealed an opening pressure of ~50 cm H2O. The CSF CrAg (cryptococcal antigen) was positive confirming a diagnosis of cryptococcal meningitis. The CD4 count later returned at a value <20 cells/mm3. A new diagnosis of AIDS was made.

What is AIDS?

  • Acquired immunodeficiency syndrome (AIDS) is defined a CD4 cell count <200 cells/mm the presence of any AIDS-defining condition (click here) irregardless of CD4 cell count.

Why is the CD4 cell count important?

  • CD4 cells or CD4 T-helper cells play an important role in calling for “back up” from other immune cells such as CD8 cytotoxic cells to kill and fight off infectious particles.
  • If CD4 cells are not produced effectively then calling for that “back up” becomes problematic.
  • If CD4 cells are depleted as is the case in HIV then infections seize the opportunity to thrive and manifest in what we know as opportunistic infections (figure 1).


Figure 1: A plot showing the association between different opportunistic infections (OIs) and CD4 cell counts.  Credit: Dr. Wayne Gold, Dr. Lapointe-Shaw (

Figure 2:  An overview of approach to illness in the patient with HIV. Credit: Dr.Paul Bunce (

What is cryptococcal meningoencephalitis?

  • This is a serious fungal opportunistic infection in patients with advanced HIV.
  • Patients can present with increased ICP with manifestations such as headache as in this case, confusion, false localizing lesions with cranial nerve palsies.
  • The pathophysiology of increased ICP in cryptococcal meningoencephalitis is not entirely clear but it is postulated to be due to blockage of arachnoid villi with fungal antigen, impairing effective CSF resorption [3].


Figure 3: Cryptococcus neoformans seen under microscopy with an India ink stain. As the with the “halo” sign due to the inability of the ink to penetrate the capsule leaving a central area of clearing appearing as a halo. Credit: wikipedia 


  1. Guidelines for the Use of Antiretroviral Agents in HIV-1-Infected Adults and Adolescents-
  2. 1993 Revised Classification System for HIV Infection and Expanded Surveillance Case Definition for AIDS Among Adolescents and Adults-
  3. Histopathology of the arachnoid granulations and brain in HIV-associated cryptococcal meningitis: correlation with cerebrospinal fluid pressure.