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. Although the ultrasound of one lymph node was unremarkable, the dynamic nature of lymph node appearance and the specific location of the new nodes are concerning for malignancy.
• Other Likely Diagnoses
  • Chronic Infection (20%): Despite the negative EBV antibody test and the low mono titer, chronic infections such as tuberculosis (TB), toxoplasmosis, or less common viral infections could explain the symptoms. The lack of response to a week's course of antibiotics does not rule out chronic infections, which may require more specific and prolonged treatments.
  • Autoimmune Disorders (15%): Conditions like rheumatoid arthritis, lupus, or sarcoidosis could present with lymphadenopathy, fatigue, and systemic symptoms. The normal LDH, CRP, and ESR do not strongly support an autoimmune process, but these conditions can have variable presentations.
  • HIV Infection (10%): Although not directly indicated by the provided tests, HIV can cause chronic lymphadenopathy, fatigue, and susceptibility to infections. The recent onset of more severe symptoms could represent an opportunistic infection or the progression of HIV to AIDS.
• Do Not Miss Diagnoses
  • Tuberculosis (5%): TB is a critical diagnosis not to miss due to its treatability and the severity of untreated disease. The presence of lymphadenopathy, fever, and systemic symptoms, even without a clear exposure history, mandates consideration of TB.
  • Other Malignancies (5%): Metastatic cancer to the lymph nodes from a primary site elsewhere in the body (e.g., lung, breast, or gastrointestinal tract) could explain the symptoms, especially the left supraclavicular lymph node, which is often associated with abdominal or thoracic malignancies.
• Rare Diagnoses
  • Castleman Disease (2%): A rare disorder that can cause lymphadenopathy, fever, and fatigue, often with an autoimmune or inflammatory component.
  • Kikuchi-Fujimoto Disease (1%): A rare, self-limiting condition that causes lymphadenopathy, fever, and night sweats, more commonly seen in young women.
  • Other Rare Infections or Inflammatory Conditions (2%): Including but not limited to histoplasmosis, coccidioidomycosis, or rare autoimmune lymphoproliferative disorders.

Justification

The percentages assigned to each category are approximate and based on the clinical presentation, the chronic nature of the symptoms, and the results of the initial diagnostic tests. The single most likely diagnosis, lymphoma, is supported by the combination of slowly growing lymph nodes, systemic symptoms, and the specific locations of the lymph nodes involved. Other likely diagnoses, such as chronic infections and autoimmune disorders, are considered due to the overlap of symptoms but are less likely given the specific findings. The "Do Not Miss" category includes diagnoses that are potentially life-threatening if not identified and treated promptly, such as tuberculosis and other malignancies. Rare diagnoses, while less likely, are included to ensure a comprehensive differential diagnosis.