What is the pathophysiology CNS cryptococcosis in HIV infection?

Updated: Jan 08, 2020
  • Author: Felicia J Gliksman, DO, MPH; Chief Editor: Niranjan N Singh, MBBS, MD, DM, FAHS, FAANEM  more...
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Answer

Answer

Cryptococcus neoformans spreads hematogenously to the CNS from pulmonary foci, which may be subclinical. No pneumonitis is found in more than 85% of patients with cryptococcal CNS disease. In addition to invading the lung and CNS, cryptococci also invade the skin, bone, and genitourinary tract, but meninges appear to be the preferred site. The reasons are not clear, but several suggestions have been made. For one, cryptococcal capsule antigens may have limited ability to induce an inflammatory response in the cerebrospinal fluid. Furthermore, the alternative pathway of complement is absent in the CSF. By contrast, CSF is a good growth medium for the organism in culture, possibly because of trophic properties of dopamine and other neurotransmitters in the CSF and the absence of cryptococcus-toxic proteins.

Cryptococcal disease usually develops only when CD4+ lymphocyte counts fall below 100 cells/μL. At this stage, macrophage function also is impaired.

Immune reconstitution inflammatory syndrome occurs in some patients after treatment with highly active antiretroviral therapy (HAART). This syndrome is a paradoxical deterioration in the clinical status despite satisfactory control of viral replication and improvement of CD4+ counts as a result of an exuberant inflammatory response toward previously diagnosed or latent opportunistic pathogens.


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