Differential Diagnosis

The patient's presentation with fever, cough, diarrhea, and malaise, particularly in the context of recent chemotherapy, suggests a complex differential diagnosis. The following categories outline potential diagnoses:

• Single Most Likely Diagnosis
  • Neutropenic Fever: This is the most likely diagnosis given the patient's recent chemotherapy, low WBC count (1200/mm^3), and symptoms of infection (fever, cough, diarrhea). Neutropenic fever is a medical emergency that requires prompt evaluation and treatment.
• Other Likely Diagnoses
  • Pneumonia: The patient's cough and fever could indicate pneumonia, especially in an immunocompromised state. The chest radiograph and blood cultures will be crucial in diagnosing this condition.
  • Gastroenteritis: Diarrhea could be indicative of a gastrointestinal infection, which is more susceptible in a patient with a compromised immune system due to chemotherapy.
  • Sepsis: Although the blood pressure is currently stable, the patient's tachycardia and fever could be early signs of sepsis, particularly if the infection is not promptly addressed.
• Do Not Miss Diagnoses
  • Invasive Fungal Infection: In immunocompromised patients, especially those with prolonged neutropenia, invasive fungal infections (e.g., aspergillosis) can be deadly if missed. Early consideration and appropriate diagnostic workup are crucial.
  • Pneumocystis jirovecii Pneumonia (PCP): This opportunistic infection can present with fever, cough, and shortness of breath in immunocompromised patients, particularly if they are not on appropriate prophylaxis.
  • Cytomegalovirus (CMV) Infection: CMV can reactivate in immunocompromised hosts, leading to a range of symptoms including fever, pneumonia, and gastrointestinal disease.
• Rare Diagnoses
  • Typhlitis (Neutropenic Colitis): A rare but serious condition that occurs in neutropenic patients, characterized by inflammation of the cecum. It presents with abdominal pain, fever, and diarrhea.
  • Drug-Induced Fever: Some medications, including certain antibiotics and antineoplastics, can cause drug fever, although this would be less likely given the patient's symptoms suggestive of an infectious process.

Each of these diagnoses requires careful consideration based on the patient's clinical presentation, laboratory results, and response to initial treatment. The key to management is prompt recognition of the likely cause of fever in a neutropenic patient and initiation of appropriate antimicrobial therapy.