Swollen lymph nodes (lymphadenopathy)

Lymph nodes are part of the immune system; they enlarge when fighting infection or when infiltrated by cancer cells. Most lymphadenopathy is reactive (response to a local or systemic infection) and resolves in 2–4 weeks. Worrying features: hard, fixed, painless nodes; supraclavicular location (especially left — Virchow's node — points to GI cancer); cervical nodes in a smoker; persistence beyond 4–6 weeks without explanation; accompanying B-symptoms (fever, night sweats, weight loss); enlarging size; age >40. Localized nodes usually point to a local cause (e.g., neck — pharyngitis, dental infection, mononucleosis; axilla — breast or arm infection; groin — leg or genital infection). Generalized lymphadenopathy (multiple node groups) points to systemic disease: viral (EBV, HIV, CMV), autoimmune (lupus, rheumatoid), lymphoma, leukaemia, sarcoidosis, drug reactions.

• Viral infections — EBV (mononucleosis), CMV, HIV, COVID-19, common URI; commonest cause.
• Bacterial infections — Streptococcal pharyngitis, tuberculosis, syphilis, cat-scratch disease.
• Dental, ENT, skin infections — drain to regional nodes.
• Autoimmune disease — systemic lupus erythematosus, rheumatoid arthritis, sarcoidosis.
• Lymphoma — Hodgkin's classically painless rubbery nodes; non-Hodgkin's variable presentation.
• Leukaemia — particularly chronic lymphocytic leukaemia in older adults.
• Metastatic cancer — breast → axilla; head and neck → cervical; GI → supraclavicular (Virchow's); melanoma.
• Medications — phenytoin, carbamazepine, allopurinol.

First-line: CBC with manual differential (look for atypical lymphocytes, blasts), CRP, LDH (rises in lymphoma), throat swab if pharyngitis, monospot/EBV serology, HIV test, ANA if autoimmune pattern. Chest X-ray for thoracic / mediastinal involvement. Mediora.AI shows the systemic markers; tissue biopsy is the definitive diagnostic test for persistent unexplained nodes and belongs with surgery + pathology.