Differential Diagnosis for LRTI in a Patient on Immunosuppression vs Disseminated CMV

• Single most likely diagnosis:
  • Disseminated CMV: This is the most likely diagnosis given the patient's immunosuppressed state, as CMV is a common opportunistic infection in such patients and can cause a wide range of symptoms including lower respiratory tract infections (LRTI).
• Other Likely diagnoses:
  • Bacterial pneumonia: Immunocompromised patients are at increased risk of bacterial infections, including those causing LRTI.
  • Pneumocystis jirovecii pneumonia (PCP): Another opportunistic infection that can cause LRTI in immunosuppressed patients.
  • Influenza or other viral pneumonias: Besides CMV, other viruses can cause LRTI in immunosuppressed patients.
• Do Not Miss (ddxs that may not be likely, but would be deadly if missed.):
  • Invasive aspergillosis: A fungal infection that can cause severe LRTI in immunosuppressed patients and has a high mortality rate if not promptly treated.
  • Tuberculosis (TB): Although less common in some regions, TB can present as LRTI and is critical to diagnose due to its treatability and public health implications.
  • Legionella pneumonia: A bacterial infection that can cause severe LRTI and has a high mortality rate if not treated appropriately.
• Rare diagnoses:
  • Nocardiosis: A rare bacterial infection that can cause LRTI in immunosuppressed patients.
  • Cryptococcal pneumonia: A fungal infection more commonly associated with central nervous system disease but can also cause LRTI in immunocompromised individuals.
  • Histoplasmosis: A fungal infection that can cause LRTI, more common in certain geographic areas and in immunosuppressed patients.