Differential Diagnosis for a 31-year-old HIV-positive Man with Respiratory Symptoms

The patient's presentation of cough, dyspnea, intermittent fevers, and oropharyngeal candidiasis, in the context of HIV infection, suggests an opportunistic infection. The differential diagnosis can be categorized as follows:

• Single Most Likely Diagnosis
  • Pneumocystis jirovecii pneumonia (PCP): This is a common opportunistic infection in HIV-positive individuals, especially those with a CD4 count below 200 cells/μL. The symptoms of cough, dyspnea, and fever are classic for PCP, making it the most likely diagnosis given the patient's HIV status and presentation.
• Other Likely Diagnoses
  • Mycobacterium tuberculosis (TB): TB is a significant concern in HIV-positive individuals due to their compromised immune status. The symptoms of cough, fever, and dyspnea could be consistent with pulmonary TB.
  • Influenza or other viral pneumonias: Given the patient's immunocompromised state, he is at higher risk for severe viral infections, including influenza.
  • Bacterial pneumonia: While less likely than opportunistic infections in an HIV-positive patient, bacterial pneumonia (e.g., due to Streptococcus pneumoniae, Haemophilus influenzae) should still be considered, especially if the patient has been exposed to others with respiratory infections.
• Do Not Miss Diagnoses
  • Kaposi's sarcoma: This is a type of cancer that can affect the lungs and is more common in HIV-positive individuals. It can present with respiratory symptoms similar to those described.
  • Lymphoma: Both Hodgkin and non-Hodgkin lymphoma can involve the lungs and present with systemic symptoms like fever and weight loss in addition to respiratory symptoms.
  • Toxoplasmosis: While more commonly associated with neurological symptoms, toxoplasmosis can cause pneumonia in immunocompromised patients.
• Rare Diagnoses
  • Histoplasmosis: A fungal infection that can cause pneumonia, more common in certain geographic areas and in immunocompromised individuals.
  • Coccidioidomycosis: Another fungal infection that can cause pneumonia, typically found in the southwestern United States.
  • Cryptococcosis: A fungal infection that can cause pneumonia and is more common in HIV-positive individuals, especially those with very low CD4 counts.

Each of these diagnoses should be considered in the context of the patient's overall clinical presentation, geographic location, and specific risk factors. Diagnostic testing, including imaging studies, blood tests, and possibly lung biopsy or bronchoscopy, may be necessary to determine the exact cause of the patient's symptoms.