Primary and Secondary Lymphoedema in Research: What the Labels Mean and Why Results Do Not Transfer Automatically

Almost every lymphoedema source uses the words "primary" and "secondary". Public health pages use them to orient readers. Consensus documents use them to organise a field. Research papers use them, often implicitly, to define who was recruited. Because the labels appear so often, it is easy to assume they mean the same thing everywhere and that a finding about one group applies to the other. This article explains what the labels do in published sources, how the study populations behind them differ, and why a result needs a careful look before it travels from one population to another.

Editorial note. This article is educational and not medically reviewed. It explains how published sources use terms and describe study populations. It does not diagnose, classify an individual, recommend treatment or predict anything about a person's health. Questions about your own swelling belong with a qualified health professional.

What the two labels do in published sources

The broad distinction is simple. Primary lymphoedema is the term used when swelling is discussed without a clear external cause and with reference to how the lymphatic system developed or functions. Secondary lymphoedema is the term used when swelling is discussed alongside another event, condition or treatment. The International Society of Lymphology 2020 consensus document and the NHS lymphoedema page both use this broad primary and secondary framing, although they serve different purposes. The consensus document speaks to professionals. The NHS page orients the public and signposts to care.

In both cases the labels organise information. They describe how a source groups histories and study populations. They are not a personal classification, and a reader cannot assign themselves to a category from a web page. Deciding which label applies to a particular person is a professional question that depends on history, examination and, where appropriate, further assessment.

How primary lymphoedema appears in research

Studies of primary lymphoedema often come from specialist settings, because the condition is less common in routine caseloads and recruitment tends to run through expert clinics. The Book 01 reference example is Schook and colleagues (2011, Plastic and Reconstructive Surgery), which reported clinical features and management in 138 paediatric patients. The cohort shows that primary lymphoedema can be described in children and that presentation can be varied.

The limits matter as much as the finding. A specialist paediatric cohort has its own recruitment pathway and clinical context. It is not a public age guide, it is not a threshold for self-assessment, and it does not describe every person with primary lymphoedema. The age at which swelling was first noticed is a point in a history, shaped by memory, attention and access to care. It is not a classifier, and it should not be read as one.

How secondary lymphoedema appears in research

Secondary lymphoedema is discussed alongside a wide range of contexts: cancer treatment, injury, infection, venous disease, reduced mobility and obesity-related overload, among others. "Associated with" is the right wording for most of these links. An association in a study population does not show that one factor caused swelling in any individual, and different contexts may involve different mechanisms.

That breadth is the reason a single "secondary lymphoedema" result is rarely a single result. A study that recruits people after a particular treatment describes one population. A study of a community caseload with mixed histories describes another. Both may use the same label in a summary, yet they ask different questions of different people.

The breast-cancer-related literature is a defined subset

A large share of the secondary lymphoedema evidence concerns breast-cancer-related populations. These studies usually define participants through a previous breast-cancer diagnosis and one or more treatments, and they often focus on unilateral arm swelling. Three UK-relevant reference points show how specific this is.

• Incidence. DiSipio and colleagues (2013, Lancet Oncology, PMID 23540561) synthesised human cohort studies in a systematic review and meta-analysis. Reported incidence varies with the definition used, the measurement instrument, the timing of assessment, the treatment group and the length of follow-up. That variation is part of the finding, not noise to be ignored.
• Trial evidence. The Cochrane reviews by Ezzo and colleagues (2015) and Stuiver and colleagues (2015) synthesise randomised trials in breast-cancer-related populations. Their conclusions apply to the populations, comparators and outcomes in those trials.
• UK guidance. NICE NG101 covers early and locally advanced breast cancer. It is breast-cancer-specific and is not general lymphoedema guidance.

Put together, these sources are strong for the question they address. They do not establish how the same intervention, measure or risk figure behaves in primary lymphoedema, in lower-limb swelling or in other secondary contexts.

Where chronic oedema fits

A third term often sits beside the first two. Chronic oedema is a wider umbrella for persistent or recurrent swelling and its practical burden. Moffatt and colleagues (2019, Lymphatic Research and Biology, PMID 30601067) studied prevalence and risk factors in UK community nursing services. The study gives a useful view of a defined service caseload. It does not establish a whole-population estimate, and it does not show that everyone in the caseload had the same lymphatic mechanism. Readers who want more on how these terms overlap can read our companion article on how lymphoedema, chronic oedema and lipoedema are used in UK sources and research.

Five words that are easy to blur

Sources about primary and secondary lymphoedema often use language that sounds similar but does different work. Keeping the words apart makes papers easier to read.

• Risk factor: something associated with a higher or lower chance of an outcome in a studied group.
• Association: a statistical relationship that does not by itself explain why it exists.
• Mechanism: a proposed or demonstrated biological pathway.
• Classification: a way of grouping conditions or populations, such as primary and secondary.
• Diagnosis: a professional judgement about an individual after assessment.

A study that reports a risk factor in a secondary lymphoedema population has not diagnosed anyone, and a classification used to organise a review does not tell an individual which group they belong to. The glossary defines these terms in the same neutral way.

Assessment and measurement add another layer

Professional assessment draws on history, examination, descriptive staging and bounded imaging where a clinician judges it useful. The ISL staging language is a way for professionals to communicate about a presentation. It is not a score a person can calculate at home. Measurement research adds further caveats. Hidding and colleagues (2016, Physical Therapy) reviewed the measurement properties of instruments for lymphedema, and Deltombe and colleagues (2007, Lymphology, PMID 17539459) compared volume methods in an upper-limb population. Both show that agreement and repeatability are tied to the instrument, the protocol and the population studied.

Patient-reported measures follow the same rule. LYMQOL (Keeley and colleagues, 2010), the Dutch LYMQOL leg validation (van de Pas and colleagues, 2016) and LYMPROM (Thomas and colleagues, 2025) were developed or validated in particular populations and languages. A questionnaire validated in one group does not automatically perform the same way in another, and none of them classifies a person as primary or secondary. Our article on patient-reported outcome measures covers this in more detail.

A transferability checklist

When a headline result mentions lymphoedema, six questions help show whether it could apply to a different population.

1. Population: who was studied, and which label did the authors use for them?
2. Definition: how did the study define lymphoedema, and by what threshold or judgement?
3. Recruitment route: did participants come from a specialist clinic, a community service, a hospital cohort or a registry?
4. Exclusions: who was left out, such as people with other conditions or earlier or milder presentations?
5. Measure: which instrument or method produced the outcome, and was it validated in this population?
6. Follow-up: how long were participants observed, and when was the outcome recorded?

If the answers differ between two studies, a comparison between them needs more than a shared label. Chapter 2 of the Book 01 evidence comparison sets out the same source-by-source approach in more depth.

What UK sources are for

UK sources answer different questions, and the primary and secondary labels carry different weight in each.

• The NHS orients the public and points toward care.
• NICE NG101 is a breast-cancer guideline. Its recommendations belong to that population.
• NICE NG141 is antimicrobial prescribing guidance for cellulitis and erysipelas. It provides infection and prescribing context only, and this article gives no antibiotic advice.
• The British Lymphology Society provides professional and service context, and the Lymphoedema Support Network provides patient information and signposting.

For a service-focused view, see the UK services context page. For the wider evidence map, see the research hub.

What these sources neither establish nor rule out

None of the sources above establishes that a single label predicts how a person's swelling will behave, which measure suits them, or which approach will help. They also do not show that results from primary and secondary populations are interchangeable. Each study answers a question about a defined group. Where evidence is thin for a population, that is a gap to describe plainly, not a reason to borrow findings from a neighbouring group.

Changing or urgent concerns

If swelling changes, becomes painful, hot or red, or comes with fever or feeling unwell, seek prompt advice from a GP, NHS 111 or emergency services as the situation requires. An article cannot assess urgency. Do not wait for more reading.

The takeaway

"Primary" and "secondary" are useful labels for organising histories and study populations. They are not diagnoses, and they are not bridges that carry a result safely from one population to another. Read the population, definition, recruitment route, exclusions, measure and follow-up first. Then decide how far a finding can reasonably travel. A reader who does this will be better prepared to ask a professional informed questions about their own situation.

Sources

1. International Society of Lymphology. The diagnosis and treatment of peripheral lymphedema: 2020 Consensus Document. Lymphology. 2020;53(1):3-19. DOI: 10.2458/lymph.4649.
2. NHS. Lymphoedema. UK public health information and signposting. nhs.uk/conditions/lymphoedema.
3. Schook CC, Mulliken JB, Fishman SJ, Grant FD, Zurakowski D, Greene AK. Primary lymphedema: clinical features and management in 138 pediatric patients. Plastic and Reconstructive Surgery. 2011;127(6):2419-2431. DOI: 10.1097/PRS.0b013e318213a218.
4. DiSipio T et al. Incidence of unilateral arm lymphoedema after breast cancer: a systematic review and meta-analysis. Lancet Oncology. 2013;14(6):500-515. DOI: 10.1016/S1470-2045(13)70076-7. PMID: 23540561.
5. Ezzo J et al. Manual lymphatic drainage for lymphedema following breast cancer treatment. Cochrane Database of Systematic Reviews. 2015;Issue 5:CD003475. DOI: 10.1002/14651858.CD003475.pub2. PMID: 25994425.
6. Stuiver MM et al. Conservative interventions for preventing clinically detectable upper-limb lymphoedema in patients at risk after breast cancer therapy. Cochrane Database of Systematic Reviews. 2015;Issue 2:CD009765. DOI: 10.1002/14651858.CD009765.pub2.
7. NICE. Early and locally advanced breast cancer: diagnosis and management. NICE guideline NG101. nice.org.uk/guidance/ng101.
8. NICE. Cellulitis and erysipelas: antimicrobial prescribing. NICE guideline NG141. nice.org.uk/guidance/ng141.
9. Moffatt CJ et al. Prevalence and risk factors for chronic edema in U.K. community nursing services. Lymphatic Research and Biology. 2019;17(2):147-154. DOI: 10.1089/lrb.2018.0086. PMID: 30601067.
10. Hidding JT et al. Measurement properties of instruments for measuring of lymphedema: systematic review. Physical Therapy. 2016;96(12):1965-1981. DOI: 10.2522/ptj.20150412.
11. Deltombe T et al. Reliability and limits of agreement of circumferential, water displacement, and optoelectronic volumetry in the measurement of upper limb lymphedema. Lymphology. 2007;40:26-34. PMID: 17539459.
12. Keeley V et al. A quality of life measure for limb lymphoedema (LYMQOL). Journal of Lymphoedema. 2010;5(1):26-37.
13. van de Pas CB et al. Validation of the Lymphoedema Quality-of-Life Questionnaire (LYMQOL) in Dutch patients diagnosed with lymphoedema of the lower limbs. Phlebology. 2016;31(4):257-263. DOI: 10.1177/0268355515586312.
14. Thomas M et al. A new validated lymphoedema-specific patient reported outcome measure (LYMPROM) for adults with lymphoedema. PLOS ONE. 2025;20(5):e0315314. DOI: 10.1371/journal.pone.0315314.
15. British Lymphology Society. Professional and service context for lymphoedema care. thebls.com. Lymphoedema Support Network. Patient information and signposting. lymphoedema.org.