Differential Diagnosis for Bilateral Enlarged Lymph Nodes

Single Most Likely Diagnosis

• Lymphoma: Given the bilateral and significant enlargement of lymph nodes, lymphoma is a strong consideration. It is a type of cancer that begins in cells of the lymph system, which is part of the immune system. The absence of STD concerns and negative TB testing helps to focus the differential towards lymphoma.

Other Likely Diagnoses

• Inflammatory or Autoimmune Conditions: Conditions such as rheumatoid arthritis, lupus, or other autoimmune diseases can cause lymphadenopathy. The presence of systemic symptoms or specific autoantibodies could support this diagnosis.
• Chronic Infections: Although TB has been ruled out, other chronic infections (e.g., toxoplasmosis, histoplasmosis) could still be considered, especially if there's a history of exposure or travel.
• Metastatic Cancer: If the patient has a known primary malignancy, metastasis to lymph nodes is a possibility. The pelvic ultrasound may provide additional information regarding potential primary sites.

Do Not Miss Diagnoses

• HIV Infection: Despite the absence of STD concerns, HIV can cause significant lymphadenopathy, especially in the early stages of infection. It's crucial to consider HIV testing, given its potential impact on management and prognosis.
• Tuberculous or Atypical Mycobacterial Infection: Although the TB test was negative, it's essential to consider the possibility of a false-negative result, especially in immunocompromised patients or those with certain types of TB.
• Sarcoidosis: This systemic granulomatous disease can cause lymphadenopathy and may not always present with typical respiratory symptoms.

Rare Diagnoses

• Castleman Disease: A rare disorder that involves an overgrowth of cells in the lymphatic system, which can cause lymphadenopathy.
• Kikuchi-Fujimoto Disease: A rare, self-limiting condition that causes lymphadenopathy, typically in young women, and is often associated with fever and night sweats.
• Rosai-Dorfman Disease: A rare histiocytic disorder that can cause lymphadenopathy and is often associated with systemic symptoms.

Each of these diagnoses requires careful consideration of the patient's clinical presentation, laboratory results, and imaging studies to determine the most appropriate next steps in management.