Lymph nodes

Structure and function

Secondary lymphoid organs distributed along the lymphatic system - sites where antigen presented by dendritic cells meets naive T and B cells, initiating the adaptive immune response
Structured into cortex (B cell follicles/germinal centres - site of B cell activation, affinity maturation, class switching), paracortex (T cell zone), and medulla (plasma cells, efferent lymphatics)
Antigen arrives via afferent lymphatics or is carried by dendritic cells from peripheral tissue -> presented to T cells in the paracortex -> activated T cells help B cells in the follicle -> germinal centre reaction produces high-affinity antibody-secreting plasma cells and memory B cells

Palpable lymphadenopathy is a common clinical finding; the overwhelming majority in primary care is reactive (benign, self-limited) rather than malignant

Clinical features favouring a reactive/benign node: tender, soft, mobile, <1cm, resolving over weeks, a clear preceding infective trigger
Features favouring malignancy: painless, firm/hard, fixed, progressive enlargement, >2cm, systemic B symptoms (fever, night sweats, weight loss), supraclavicular location (higher malignancy risk regardless of size)
Excisional biopsy (not fine-needle aspiration alone) is preferred when lymphoma is suspected, since architecture is needed for accurate subtyping

Reactive lymphadenopathy - treat the underlying infective/inflammatory trigger, most resolve without specific intervention
Persistent, enlarging, or high-risk-feature lymphadenopathy warrants biopsy rather than a trial of antibiotics or watchful waiting alone

Infection (viral - most common cause of generalised lymphadenopathy; bacterial - localised), lymphoma, metastatic carcinoma, autoimmune disease (SLE, RA), sarcoidosis

A reactive node typically shrinks over 2-4 weeks as the triggering process resolves; lymphadenopathy persisting or enlarging beyond this window warrants further investigation rather than continued observation

5 more sections, plus exam facts

Premium unlocks every note across every specialty, and the full exam fact library behind it.