This patient's presentation of headache, nuchal rigidity, and the LP results noted in the question stem is consistent Cryptococcus neoformans meningitis. This organism's soluble polysaccharide antigen causes latex bead agglutination of CSF fluid samples.
Cryptococcus neoformans exists in yeast form only and is marked by narrow-based budding and large capsules that are seen on staining with India ink. This organism is a common cause of meningitis and meningoencephalitis in immunocompromised patients. Typically, patients are not susceptible to Cryptococcus neoformans CNS infections until their CD4 count falls below 50 cells/mm^3. It is present in soil and pigeon droppings and infects via respiratory transmission. Treatment includes amphotericin B and flucytosine for acute meningitis and fluconazole for prophylaxis.
Capoor et al. review the diagnosis of Cryptococcus neoformans; they find that diagnosis at an early stage is often difficult due to the non-specific clinical presentation and radiological evidence of infection. Diagnostic approaches include: conventional culture methods, latex agglutination test, and molecular methods such as polymerase chain reaction (PCR).
Newton reviews the timeline of potential complications in HIV infection. Acute encephalitis, aseptic meningitis, and acute demyelinating polyneuropathy all typically occur relatively early in the course of the disease. Dementia, central nervous system-related cancer, opportunistic infections (such as with C. neoformans), and autonomic neuropathy usually present later in the course of the infection.
Illustration A shows Cryptococcus neoformans stained with India ink.
Answer 1: Cotton-wool spots on funduscopic exam can be a sign of cytomegalovirus (CMV) induced retinitis in immunocompromised patients.
Answer 2: Ring enhancing lesions on CT imaging are diagnostic of brain abscesses or CNS lymphoma. Toxoplasma gondii causes brain abscesses in AIDS patients. These can usually be distinguished because CNS lymphoma is a single lesion and toxoplasma gondii usually has multiple foci.
Answer 4: In AIDS patients, acid-fast cysts in stool are indicative of cryptosporidium spp. infection.
Answer 5: Frontotemporal atrophy is indicative of frontotemporal dementia.
Capoor MR, Nair D, Deb M, Gupta B, Aggarwal P. Clinical and mycological profile of cryptococcosis in a tertiary care hospital. Indian J Med Microbiol. 2007 Oct;25(4):401-4
PMID:18087095 (Link to Abstract)
Newton HB. Common neurologic complications of HIV-1 infection and AIDS. Am Fam Physician. 1995 Feb 1;51(2):387-98.
PMID:7840035 (Link to Abstract)
USMLE World Step 1 QBank Question #118. Copyright © USMLEWorld, LLC 2012.