Differential Diagnosis for Recurring Episodes of Fever

The patient's presentation of recurring single episodes of fever, loss of appetite, and a history of upper respiratory tract (URT) infection and allergic bronchitis, without evidence of chest infection, jaundice, or anemia, suggests a range of potential diagnoses. Here's a categorized differential diagnosis:

• Single Most Likely Diagnosis
  • Infectious Mononucleosis (Mono): Although more common in younger populations, mono can occur at any age. The recurring fever, loss of appetite, and history of URT infection could align with this diagnosis, especially if the initial URT infection was caused by Epstein-Barr virus (EBV).
• Other Likely Diagnoses
  • Chronic Fatigue Syndrome: Given the history of URT infection and the ongoing symptoms of fever and loss of appetite without clear evidence of infection, chronic fatigue syndrome could be considered, especially if the patient reports persistent fatigue.
  • Autoimmune Disorders (e.g., Rheumatoid Arthritis, Lupus): These conditions can present with recurring fevers, loss of appetite, and a history of infections or allergic reactions, although specific diagnostic criteria and additional symptoms would be needed for a definitive diagnosis.
  • Recurrent Infections: The patient's history of URT infection and allergic bronchitis, followed by recurring fevers, might suggest an underlying issue with the immune system, making the patient more susceptible to infections.
• Do Not Miss Diagnoses
  • Tuberculosis (TB): Although the patient does not have evidence of chest infection, TB can present in various forms, including extrapulmonary TB, which might not initially involve the lungs. The recurring fevers and loss of appetite are red flags.
  • Lymphoma: This is a critical diagnosis not to miss, as it can present with recurring fevers, night sweats, and loss of appetite. A history of recurrent infections or autoimmune disorders might also be relevant.
  • Endocarditis: Although less likely without specific cardiac risk factors or signs of infection, endocarditis can cause recurring fevers and should be considered, especially if the patient has a history of heart disease.
• Rare Diagnoses
  • Periodic Fever Syndromes: These are a group of disorders characterized by recurring episodes of fever, often with other symptoms like abdominal pain or rash. They are rare and usually have a genetic basis.
  • Castleman Disease: A rare disorder that can cause recurring fevers, weight loss, and fatigue, among other symptoms. It involves an overgrowth of cells in the body's lymph nodes.

Each of these diagnoses requires careful consideration of the patient's full clinical picture, including laboratory tests, imaging studies, and potentially, specialist consultations to determine the underlying cause of the recurring fevers.