Differential Diagnosis for Prolonged Fever

The patient presents with a 45-day history of fever without a clear cause, despite multiple antibiotic treatments, and has leukopenia with a WBC count of 1650, normal platelet count, normal liver and kidney function tests, and other negative or normal investigations.

• Single Most Likely Diagnosis
  • Tuberculosis (TB): Given the prolonged fever, lack of response to broad-spectrum antibiotics, and the presence of leukopenia, TB is a strong consideration. It can present with a wide range of symptoms, including prolonged fever, and can affect various parts of the body. The raised LDH could also be indicative of TB, especially if it involves the lymph nodes or other organs.
• Other Likely Diagnoses
  • Endocarditis: Although the 2D echo is reported as normal, the possibility of endocarditis cannot be entirely ruled out without further investigation, especially if the patient has a history of heart disease or intravenous drug use. The prolonged fever and lack of response to antibiotics could suggest this diagnosis.
  • Lymphoma: The presence of prolonged fever, leukopenia, and a raised LDH level could suggest a hematological malignancy like lymphoma. Further investigations, including imaging and possibly a biopsy, would be necessary to confirm this diagnosis.
  • Chronic Q Fever: This is another infection that can cause prolonged fever and does not always respond to standard antibiotic treatments. It's less common but should be considered, especially if the patient has been exposed to animals.
• Do Not Miss Diagnoses
  • HIV/AIDS: Given the patient's prolonged fever, leukopenia, and lack of response to antibiotics, HIV/AIDS is a critical diagnosis not to miss. The patient's HIV status is awaited, and this diagnosis could explain many of the patient's symptoms and findings.
  • Brucellosis: This zoonotic infection can cause prolonged fever, and its diagnosis is often missed. It requires specific cultures or serological tests for diagnosis.
  • Fungal Infections: In immunocompromised patients or those with specific exposures, fungal infections can cause prolonged fever. Although the patient's immune status is not clearly compromised, this should be considered, especially if other diagnoses are ruled out.
• Rare Diagnoses
  • Whipple's Disease: A rare, systemic bacterial infection that can cause fever, weight loss, and malabsorption. It's very rare but can be fatal if not treated.
  • Adult-Onset Still's Disease: An autoimmune condition characterized by high fevers, joint pain, and rash. It's rare and can be difficult to diagnose but should be considered in the differential for prolonged fever of unknown origin.
  • Kikuchi-Fujimoto Disease: A rare condition that can cause lymphadenopathy, fever, and leukopenia. It's more common in young women and can be self-limiting but should be considered in the differential diagnosis.

Each of these diagnoses requires careful consideration of the patient's clinical presentation, laboratory findings, and exposure history. Further diagnostic testing, including specific cultures, serologies, imaging, and possibly biopsies, will be necessary to determine the underlying cause of the patient's prolonged fever.