Differential Diagnosis

The patient presents with a complex set of symptoms including swollen lymph nodes, fatigue, appetite loss, nausea, lightheadedness, and fever. Given the duration and progression of symptoms, along with the laboratory and imaging findings, the differential diagnosis can be categorized as follows:

• Single Most Likely Diagnosis

  • Lymphoma (40%): The slow growth of lymph nodes over three years, recent worsening of symptoms, and the appearance of new lymph nodes, including a left supraclavicular node, are highly suggestive of lymphoma. The lack of improvement with antibiotics and the presence of systemic symptoms such as fever and night sweats (implied by the worsening condition) further support this diagnosis.

• Other Likely Diagnoses

  • Chronic Infection (20%): Despite the negative EBV antibody test and the low mono titer, chronic infections such as tuberculosis or toxoplasmosis could explain the prolonged course of symptoms. The recent worsening could indicate a change in the disease process or the development of a new infection.
  • Autoimmune Disorder (15%): Conditions like rheumatoid arthritis or lupus can cause prolonged fatigue, fever, and lymphadenopathy. The normal inflammatory markers (LDH, CRP, ESR) do not rule out autoimmune disorders, as these can be normal in certain phases of the disease.
  • HIV Infection (10%): HIV can cause chronic lymphadenopathy, fatigue, and susceptibility to infections. The absence of risk factors is not sufficient to rule out HIV, and the recent worsening of symptoms could indicate progression to AIDS.

• Do Not Miss Diagnoses

  • Tuberculosis (5%): TB is a critical diagnosis not to miss due to its treatability and potential for severe consequences if left untreated. The presence of lymphadenopathy, fever, and systemic symptoms, even without a clear exposure history, mandates consideration of TB.
  • Metastatic Cancer (5%): Although less likely given the age and the slow progression, metastatic cancer to the lymph nodes from a primary site (e.g., the left supraclavicular node could indicate abdominal or thoracic malignancy) is a diagnosis that must be considered due to its significant implications.

• Rare Diagnoses

  • Castleman Disease (2%): A rare disorder that can cause lymphadenopathy, fever, and systemic symptoms. It is less likely but should be considered in the differential due to its unique presentation and treatment options.
  • Sarcoidosis (3%): Although it can cause lymphadenopathy and systemic symptoms, the lack of respiratory symptoms or other organ involvement makes this less likely. However, it remains a consideration in the broad differential diagnosis of lymphadenopathy and systemic illness.

The percentages assigned to each category are approximate and based on the clinical presentation, reflecting the relative likelihood of each diagnosis given the information provided. The mono titer test being positive at 1:2 could be a false positive, especially given the negative EBV antibody test result. Further diagnostic workup, including biopsy of the lymph nodes and additional laboratory tests, is necessary to establish a definitive diagnosis.