Definitions and staging

Evidence in one minute

• Lymphoedema is low-output failure of lymph transport — primary (developmental) or secondary (surgery, radiotherapy, infection, filariasis, trauma); ~85% worldwide is secondary. High-output oedema (heart, liver, kidney, venous) is different, but long-standing high-output states can damage lymphatics and become mixed. Executive Committee of the International Society of Lymphology 2023
• Chronic oedema = swelling present ≥3 months; Wounds Canada 2025 treats all chronic oedema as lymphatic dysfunction — a deliberately broad definition. Keast 2025 · Charles 2013
• ISL stages: 0 latent (measurable only — BIS, TDC); I pitting, reduces with elevation; II fat and fibrosis, elevation rarely helps; III lymphostatic elephantiasis. A limb can carry more than one stage.
• Severity (unilateral): minimal/mild >5 to <20% excess volume; moderate 20–40%; severe >40%.
• Primary lymphoedema by age: congenital (<2 y), praecox (2–35 y), tarda (>35 y); familial forms warrant genetic testing (FOXC2, FLT4/VEGFR-3, VEGFC, SOX18, GJC2, PIEZO1, GATA2 and others).
• Lipoedema is not lymphoedema (fat disorder sparing hands and feet; Stemmer negative) but can progress to lipo-lymphoedema. Lipoedema
• SA usage: the LAOSA statement adopts ISL staging and the same primary/secondary split. Davey 2018

Certainty: definitions and staging are consensus (LoE 5), internationally agreed; severity bands are conventional rather than outcome-validated.