Mr. L is a 35-year-old man who is HIV-positive. His chief complaints are cough and fever lasting for 4 days.
What is the differential diagnosis of cough and fever in HIV-positive patients? How would you frame the differential?
CONSTRUCTING A DIFFERENTIAL DIAGNOSIS
The most common pneumonias in HIV-infected patients are bacterial pneumonia, PJP, and pulmonary TB. Taken together, they account for 91% of pulmonary infections in HIV-positive patients. Three pivotal features aid in the diagnosis of these common pneumonias in HIV-infected persons. First, the CD4TL count gauges the level of immunocompromise. Virulent infections, such as pulmonary TB or bacterial pneumonia, may occur in patients with any CD4TL count. On the other hand, less virulent infections, such as PJP, are seen almost exclusively in patients with CD4TL < 200 cells/mcL.
The second pivotal feature is that certain diseases present acutely (bacterial pneumonia), but other diseases present subacutely or chronically (pulmonary TB or PJP).
The final pivotal feature that aids in the diagnosis of these complaints is the pattern on chest radiograph. Lobar infiltrates suggest bacterial pneumonia, whereas diffuse or interstitial infiltrates are seen in PJP and TB. Patterns that suggest pulmonary TB include apical or cavitary infiltrates (if CD4TL > 200 cells/mcL), hilar lymphadenopathy, or nodular infiltrates. The chest radiographic pattern in pulmonary TB varies depending on the patient’s degree of immunosuppression. Table 5-4 summarizes the typical CD4TL count, acuity, and chest radiographic pattern and approach to pulmonary infection in HIV-positive patients.
Table 5-4.Summary of findings in pulmonary infection in HIV-positive patients. ||Download (.pdf) Table 5-4. Summary of findings in pulmonary infection in HIV-positive patients.
|Variable ||Tuberculosis ||Bacterial Pneumonia ||PJP |
|Acuity || |
Weeks to months
< 1 week
Weeks to months
|CD4 ||Any count ||Any count ||< 200/mcL |
|Typical chest radiographic pattern || |
CD4 > 200 /mcL: Apical, cavitary or nodular lesions
CD4 < 200 /mcL: Normal, or middle or lower lobe consolidation, miliary pattern, lymphadenopathy
|Lobar consolidation ||Bilateral perihilar diffuse symmetric interstitial pattern |
|Risk factors ||Foreign born or traveler to endemic area, recent exposure, prior positive PPD or IGRA, injection drug use, prison || |
Injection drug use
Low CD4 count increases risk
|Low CD4 count |
|Other clues ||Pleural effusions may be seen || ||Elevated lactate dehydrogenase, more hypoxia than expected from chest radiographic findings |
|Diagnostic tests of choice || |
Sputum smear and culture.
BAL if no productive cough;
Biopsy if miliary TB
|Sputum culture, Gram stain and blood culture || |
Sputum obtained by BAL1
Silver stain, H&E, or DFA for PJP
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