What causes swollen lymph nodes?

Causes of Swollen Lymph Nodes

Swollen lymph nodes result from three primary mechanisms: infection (most common), malignancy, or inflammatory/autoimmune conditions, with the specific cause determined by node characteristics, location, and associated symptoms. 1

Infectious Causes

Bacterial Infections

• Acute bacterial lymphadenitis presents with rapid onset, tender nodes, fever, and erythema, often with suppurative necrosis and abscess formation requiring antibiotic therapy 2, 3
• Cat-scratch disease (Bartonella henselae) develops 3 weeks after inoculation, causing regional adenopathy that may suppurate in 10% of cases and typically resolves within 1-6 months 2
• Nontuberculous mycobacterial (NTM) lymphadenitis affects children aged 1-5 years, presenting as unilateral, non-tender cervical/submandibular nodes—the lack of tenderness distinguishes it from bacterial causes 2, 4
• Tuberculous lymphadenitis causes significant adenopathy without marked pain 4
• Anthrax produces painless lesions with regional lymphadenopathy, though mortality without treatment can reach 20% 2

Viral Infections

• Upper respiratory tract infections most commonly cause enlarged jugulodigastric (tonsillar) nodes, representing the single most frequent etiology of cervical lymphadenopathy 5
• Adenoviral conjunctivitis can cause palpable preauricular nodes with follicular conjunctival reaction 2
• Herpes simplex virus (HSV) typically produces unilateral disease with palpable preauricular nodes and distinctive vesicular rash 2
• Infectious mononucleosis causes nonspecific follicular and paracortical hyperplasia that may mimic lymphoma 3
• HIV/AIDS presents with generalized lymphadenopathy as a systemic manifestation, and disseminated MAC infection in AIDS patients causes suppurative lymphadenopathy with swollen, painful cervical, axillary, or inguinal nodes during immune reconstitution syndrome 2, 5

Other Infectious Agents

• Toxoplasma lymphadenitis displays follicular hyperplasia, monocytoid B-cell hyperplasia, and clusters of epithelioid histiocytes 3
• Fungal infections produce granulomatous inflammation patterns 3

Malignant Causes

Lymphoma

• Conjunctival lymphoma presents as unilateral, painless, "salmon patch" swelling, with 20% developing systemic disease; associated with immune deficiency, autoimmune conditions (Sjögren's, Hashimoto's, IgG4-related disease), and chronic infections 2
• Hodgkin and non-Hodgkin lymphoma present with painless adenopathy that can mimic infectious conditions like Kikuchi-Fujimoto lymphadenitis 4, 3
• Chronic myeloid leukemia (CML) rarely causes lymphadenopathy directly—swollen nodes in CML patients may indicate concurrent lymphoma rather than CML manifestation 6

Metastatic Disease

• Breast cancer metastases to axillary nodes may be detected on mammography/tomosynthesis, with morphologically abnormal nodes requiring further breast parenchyma evaluation 2
• Ocular surface squamous neoplasia and melanoma can cause regional metastases with associated lymphadenopathy 2
• Carcinoma in the drainage area of head and neck structures commonly metastasizes to cervical nodes 5

Inflammatory and Autoimmune Causes

• Autoimmune lymphoproliferative syndrome reflects underlying immune system abnormalities presenting with reactive lymphadenopathy 7
• Kikuchi-Fujimoto lymphadenitis displays necrotizing histiocytic patterns that may mimic malignant lymphoma 3
• Kawasaki disease in children presents with cervical lymphadenopathy ≥1.5 cm that may be firm and slightly tender or non-tender 4
• Silicone adenitis from breast implant rupture shows "snowstorm" appearance on ultrasound in axillary nodes containing free silicone 2

Secondary Lymphedema-Related Causes

• Post-surgical lymph node dissection (especially axillary dissection for breast cancer) damages lymphatic drainage, increasing cellulitis risk that presents with painful adenopathy requiring urgent antibiotics 8, 9
• Radiation therapy to supraclavicular or axillary nodes increases secondary lymphedema risk with recurrent infections causing progressive adenopathy 8

Critical Diagnostic Features

High-Risk Characteristics Requiring Urgent Evaluation

• Nodes >2 cm, hard, or matted/fused to surrounding structures indicate malignancy or granulomatous disease, particularly in children 1
• Epitrochlear or supraclavicular location carries higher malignancy risk regardless of other features 1
• Lymphadenopathy persisting >4 weeks or accompanied by fever, night sweats, and unintentional weight loss mandates imaging and laboratory studies (CBC, CRP, ESR, tuberculosis testing) 1
• Generalized lymphadenopathy (multiple node regions) usually indicates systemic disease rather than localized infection 1

Distinguishing Tender vs. Non-Tender Nodes

• Tender nodes with rapid onset suggest acute bacterial infection requiring antibiotics 4, 1
• Painless, persistent nodes raise concern for malignancy (lymphoma, metastatic disease) or chronic infections (NTM, tuberculosis) requiring biopsy 4, 1