Chapter 20: The Immune System and Infection
A 50-year-old HIV-positive man presents to the emergency department (ED) with complaints of headache, fever (100.4–101.3°F) and confusion for the past 10 days. His physical examination is normal except for a decreased performance on mini–mental status examination. His chest radiograph and CT show right lower lobe consolidation and large pleural effusion. His labs show the following:
|WBC ||14 × 103/μL |
|Hemoglobin ||13 g/dL |
|Platelets ||300 × 103/μL |
|Sodium ||145 mEq/L |
|Potassium ||4 mEq/L |
|Chloride ||110 mEq/L |
|CO2 ||26 mEq/L |
|Blood urea nitrogen ||30 mg/dL |
|Creatinine ||1.6 mg/dL |
|Calcium ||8 mg/dL |
|Glucose ||100 mg/dL |
|Lactic acid ||3 mmol/L |
The patient proceeds to have a thoracentesis, which showed the following:
Pleural fluid stained with India ink is positive for Cryptococcus. What is the next step?
C. Serial serum Cryptococcus antigen
The patient has been diagnosed with pulmonary Cryptococcus. This fungus has a penchant for dissemination into the central nervous system, manifesting usually as meningoencephalitis and, in rare instances, as brain abscess. A CT head would be the appropriate initial step in patients who are immunocompromised and have CNS symptoms. This is followed by lumbar puncture (choice B) for evaluation of opening pressure as a surrogate to intracranial pressure and to obtain specimen for cerebrospinal fluid culture. Lumbar puncture may be repeated 2 weeks after induction therapy to determine whether pressures have improved and cerebrospinal fluid culture is cleared from Cryptococcus. Initial treatment is amphotericin B with flucytosine, due to its better penetration to the blood–brain barrier, for 2 weeks, followed by consolidation treatment with fluconazole (choice A) for 8 weeks. Serial Cryptococcus antigen (choice C) is only indicated when maintenance therapy is being discontinued. An initial serum or cerebrospinal fluid cryptococcal antigen might be useful if the diagnosis is not confirmed, since cultures can be falsely negative and/or take time to become positive.
A 65-year-old woman, a farmer from south Ohio, presents with low-grade fever, dry cough, and chest pain for 4 months. Physical examination reveals a temperature of 102.5°F. A chest radiograph reveals an apical consolidation with cavities in the right upper lobe. Her lung biopsy, shown below, depicted organisms within macrophages that stained positive with Gomori methenamine silver (GMS) (Fig. 20-2). What is the most likely diagnosis?