Chronic primary pain: Understanding ICD‑11 and the Difference Between Primary and Secondary Pain
Chronic pain can be associated with an identifiable disease, injury or lesion. In other situations, pain becomes the main health condition requiring assessment and treatment, even though no other diagnosis adequately accounts for the overall presentation.
The International Classification of Diseases, 11th Revision—usually called ICD‑11—recognises both possibilities. It classifies chronic pain as either chronic primary pain or one of several forms of chronic secondary pain. This distinction can improve diagnosis, communication and treatment planning, but it does not imply that one type of pain is more real or more serious than another.[1–3]
WHAT IS ICD‑11?
ICD‑11 is the World Health Organization’s international system for classifying diseases and health conditions. Unlike earlier versions, it contains a dedicated chronic pain classification.
ICD‑11 generally defines chronic pain as pain that persists or recurs for longer than three months. It then distinguishes between pain that is considered a health condition in its own right and pain attributed to another underlying condition.[1,2]
Importantly, ICD‑11 is a classification system. It helps clinicians describe and code a condition, but it does not provide a complete explanation of an individual person’s pain and does not determine treatment by itself.
WHAT IS CHRONIC PRIMARY PAIN?
Chronic primary pain is pain in one or more parts of the body that meets three central criteria:
It persists or recurs for longer than three months.
It is associated with significant pain-related emotional distress or functional disability, such as interference with daily activities, work, relationships or social participation.
It is not better accounted for by another chronic pain diagnosis.[3,4]
The requirement is distress or disability; a person does not need to have both. Emotional distress in this context refers to distress associated with living with pain. It does not mean that distress caused the pain or that the pain is psychological.
Chronic primary pain may be diagnosed even when biological, psychological or social contributors have been identified, provided that another chronic pain diagnosis does not better account for the overall presentation.[3,4]
“Primary” does not mean “imaginary”
The word primary can be misunderstood. It does not mean:
that the pain is “all in the mind”;
that no biological processes are involved;
that all scans and tests must be normal;
that the person has not been investigated properly; or
that psychological treatment is the only appropriate treatment.
Instead, it means that pain itself has become the predominant health condition requiring care, rather than being adequately classified as a consequence of another disease or injury.
A person may have structural findings on a scan and still meet the criteria for chronic primary pain if those findings do not adequately account for the pain presentation. Conversely, a normal scan does not establish chronic primary pain by itself.
TYPES OF CHRONIC PRIMARY PAIN
CHRONIC SECONDARY PAIN
The current ICD‑11 classification includes several chronic primary pain groups:
Chronic primary visceral pain — MG30.00: including chronic primary abdominal, pelvic, bladder, chest or epigastric pain syndromes.
Chronic widespread pain — MG30.01: including fibromyalgia syndrome.
Chronic primary musculoskeletal pain — MG30.02: including some presentations of chronic low back, neck, thoracic or limb pain.
Chronic primary headache or orofacial pain — MG30.03: covering selected primary headache and facial pain syndromes.
Complex regional pain syndrome — MG30.04: a distinct regional pain syndrome with sensory, autonomic, inflammatory and motor features.
Not every person with back pain, pelvic pain, headache or widespread pain has chronic primary pain. The relevant diagnostic criteria must still be met, and other plausible causes must be considered.
ICD‑11 is digitally maintained and may be updated as medical knowledge and classification practices evolve. Code placement should therefore be checked against the current WHO release when formal coding is required.[1,4]
WHY PRIMARY VS SECONDARY MATTERS FOR PATIENTS
This classification reduces confusion and stigma by:
Validating experience: Primary pain is a legitimate diagnosis, not "nothing wrong on scans."[5][2]
Guiding treatment: Primary pain responds better to nervous system modulation, education, and psychological therapies than structural interventions.[3]
Improving communication: Clear codes help doctors, insurers, and patients align on diagnosis and care plans.[6]
WHAT IS CHRONIC SECONDARY PAIN?
In chronic secondary pain, another disease, injury or pathological process is considered sufficiently likely to account for the pain.
ICD‑11 divides chronic secondary pain into six main groups:
Chronic cancer-related pain - Pain caused by cancer, metastases or cancer treatment.
Chronic postsurgical or post-traumatic pain - Pain that develops or increases following surgery or tissue injury and persists beyond the expected healing period.
Chronic secondary musculoskeletal pain - Pain attributed to ongoing musculoskeletal inflammation, disease or structural change, such as inflammatory arthritis or a symptomatic fracture.
Chronic secondary visceral pain - Pain attributed to an identified disease or disorder of an internal organ.
Chronic neuropathic pain - Pain caused by a lesion or disease of the somatosensory nervous system, such as painful diabetic neuropathy or some forms of radiculopathy.
Chronic secondary headache or orofacial pain - Headache or facial pain attributed to another underlying disorder.
For a secondary-pain diagnosis, the relationship between the underlying condition and the pain should be clinically plausible. Finding arthritis, disc degeneration or another abnormality does not automatically prove that it is the principal cause of a person’s pain.[1,2,4]
CAN PRIMARY AND SECONDARY PAIN OCCUR TOGETHER?
Yes. The categories are not always mutually exclusive.
For example, a person may have chronic secondary pain associated with knee osteoarthritis and also meet criteria for chronic widespread primary pain. Another person may have persistent pain after surgery together with additional pain that is not adequately explained by the operation or resulting tissue injury.
Different contributors may also become more or less important over time. Assessment and treatment should therefore address the whole clinical presentation rather than forcing every symptom into a single category. NICE explicitly recognises that chronic primary and chronic secondary pain may coexist and recommends that management be guided by both conditions when this occurs.
IS CHRONIC PRIMARY PAIN THE SAME AS NOCIPLASTIC PAIN?
No. These terms describe different aspects of pain.
Chronic primary pain is a diagnostic and classification category. Nociplastic pain is a mechanistic descriptor used when pain appears to involve altered nociception and is not fully explained by ongoing tissue damage activating nociceptors or by a lesion or disease of the somatosensory nervous system.[5,6]
Clinicians also use the following mechanistic terms:
Nociceptive pain: associated with actual or threatened injury to non-neural tissue and activation of nociceptors.
Neuropathic pain: caused by a lesion or disease of the somatosensory nervous system.
Nociplastic pain: associated with altered nociception that is not adequately explained by nociceptive or neuropathic mechanisms.
Nociplastic mechanisms may be relevant in chronic primary pain conditions such as fibromyalgia, but the terms should not be treated as synonyms. Nociplastic, nociceptive and neuropathic mechanisms may also coexist within the same person.[5,6]
What about central sensitisation?
Central sensitisation refers to increased responsiveness of pain-related neurons within the central nervous system. It is one possible process that may contribute to pain hypersensitivity.
Features such as pain from normally non-painful touch, increased pain from pressure or pain extending beyond the original site may suggest altered pain processing. However, these findings are not unique to chronic primary or nociplastic pain.
Central sensitisation is a neurophysiological concept rather than a diagnosis that can be confirmed by a routine scan, blood test or questionnaire. In clinical practice, it can only be inferred indirectly and should not be presented as the sole explanation for every case of persistent pain.[5,6]
THE ROLE OF BIOLOGICAL, PSYCHOLOGICAL AND SOCIAL FACTORS
Pain is influenced by interacting biological, psychological and social factors. These may include:
tissue and nervous-system processes;
physical health and other medical conditions;
sleep and fatigue;
anxiety, depression or trauma-related symptoms;
attention, expectations and previous experiences;
work, family and financial pressures; and
access to healthcare, social support and opportunities for activity.
This does not mean that psychological or social factors make pain less real. Similar factors influence the severity, consequences and recovery trajectory of many health conditions.
A biopsychosocial assessment is intended to understand the whole person and identify potentially modifiable contributors—not to divide pain into “physical” and “psychological” categories.
HOW IS CHRONIC PRIMARY PAIN DIAGNOSED?
There is no single blood test, scan or biomarker that confirms all forms of chronic primary pain.
Diagnosis usually involves:
a detailed history of the pain and associated symptoms;
assessment of physical function, sleep, mood, work and social participation;
physical and neurological examination;
review of previous injuries, illnesses, investigations and treatments;
consideration of primary and secondary pain diagnoses; and
targeted investigations when indicated by the history, examination or possible warning features.
Chronic primary pain should not be regarded simply as a diagnosis made because “all the tests were normal”. It is a positive clinical formulation based on the duration, pattern and impact of pain, together with an assessment of whether another diagnosis better accounts for the presentation.[3,4]
At the same time, the label should not prevent further assessment when symptoms change. New neurological symptoms, systemic illness, significant trauma or another important change in the clinical pattern may require reconsideration of the diagnosis.
HOW IS CHRONIC PRIMARY PAIN MANAGED?
There is no single treatment for all chronic primary pain conditions. Management should be matched to the particular pain syndrome, contributing mechanisms, coexisting health conditions, personal circumstances and goals.
The aim is not simply to choose between “treating the body” and “treating the mind”. Good pain care may address pain intensity, physical capacity, sleep, emotional wellbeing, medication safety, work, relationships and participation in valued activities.
Understanding the condition
A clear and non-stigmatising explanation can help a person understand why pain may persist and how different contributors can be addressed. Education should support shared decision-making and self-management, but it should not be presented as a standalone cure.
Physical activity and exercise
Appropriately selected physical activity may improve physical function, confidence, general health and, for some people, pain. Programs should be adapted to the person’s health, abilities, preferences and symptoms.
Research across chronic pain conditions supports physical activity as part of care, although the average benefits are generally modest and the certainty of evidence varies between conditions and exercise approaches. Claims that a particular form of exercise reliably reduces pain by a fixed percentage are therefore not justified.[7,8]
Psychological treatment for pain
Pain-focused psychological therapies may include cognitive behavioural therapy and acceptance and commitment therapy. These treatments can help some people reduce pain-related distress, improve coping and participation, address fear or avoidance, and respond more flexibly to symptoms.
They are offered because thoughts, emotions, behaviour and context influence every pain experience—not because the pain is imagined. Systematic-review evidence suggests that the average benefits of cognitive behavioural approaches are small, although individual responses vary.[7,9]
Sleep, mental health and social factors
Sleep disorders, depression, anxiety, post-traumatic symptoms, substance use, social isolation and workplace difficulties may increase the overall burden of pain. Addressing these concerns can be an important part of treatment while the pain itself continues to be assessed and treated.
Medication
Medication decisions should be individualised and based on the specific pain condition rather than the broad label of chronic primary pain.
Some guidelines advise considering selected antidepressant medicines for certain adults with chronic primary pain after discussing possible benefits, adverse effects and personal preferences. Their use does not imply that the pain is caused by depression.
The NICE guideline advises against initiating opioids or gabapentinoids solely to treat chronic primary pain. Gabapentinoids may nevertheless have a role in selected people with confirmed neuropathic pain, which is a separate ICD‑11 category. Existing medication should be reviewed with the prescriber and should not be stopped abruptly without appropriate clinical advice.[7]
Procedures and surgery
A chronic primary pain diagnosis does not automatically exclude procedures or surgery. These treatments may be appropriate when assessment identifies a specific coexisting condition or pain source for which the proposed intervention has a reasonable evidence base.
However, repeated structure-focused treatment is less likely to help when the proposed target does not adequately correspond with the person’s symptoms and clinical findings. Any invasive treatment should have a clear indication, realistic objectives and an individual discussion of alternatives, limitations and risks.
Interdisciplinary care
People with high-impact or complex pain may benefit from coordinated input from several disciplines, such as pain medicine, general practice, physiotherapy, psychology, occupational therapy, nursing or other relevant specialties.
Interdisciplinary treatment is not necessarily intended to eliminate every symptom. It may help a person improve function, reduce pain-related distress, use medication more safely and return to meaningful activities.
General information disclaimer
This article provides general educational information and is not a substitute for individual medical assessment, diagnosis or treatment. It does not recommend any specific investigation, medicine, procedure or other therapy. Treatment suitability varies according to the diagnosis, medical history, other medications and individual circumstances. Concerns about persistent pain should be discussed with an appropriately qualified health practitioner.
Last medically reviewed: 15/08/2026
REFERENCES
World Health Organization. International Classification of Diseases, Eleventh Revision: ICD‑11 for Mortality and Morbidity Statistics—MG30 Chronic Pain. WHO; current online release.
Treede RD, Rief W, Barke A, et al. Chronic pain as a symptom or a disease: the IASP classification of chronic pain for the International Classification of Diseases (ICD‑11). Pain. 2019;160(1):19–27. doi:10.1097/j.pain.0000000000001384.
Nicholas M, Vlaeyen JWS, Rief W, et al. The IASP classification of chronic pain for ICD‑11: chronic primary pain. Pain. 2019;160(1):28–37. doi:10.1097/j.pain.0000000000001390.
International Association for the Study of Pain. Definitions of Chronic Pain Syndromes. IASP.
International Association for the Study of Pain. IASP Terminology: Nociceptive Pain, Nociplastic Pain and Sensitisation. IASP.
Kosek E, Clauw D, Nijs J, et al. Chronic nociplastic pain affecting the musculoskeletal system: clinical criteria and grading system. Pain. 2021;162(11):2629–2634. doi:10.1097/j.pain.0000000000002324.
National Institute for Health and Care Excellence. Chronic Pain (Primary and Secondary) in Over 16s: Assessment of All Chronic Pain and Management of Chronic Primary Pain. NICE guideline NG193. 2021.
Geneen LJ, Moore RA, Clarke C, Martin D, Colvin LA, Smith BH. Physical activity and exercise for chronic pain in adults: an overview of Cochrane Reviews. Cochrane Database Syst Rev. 2017;(1):CD011279. doi:10.1002/14651858.CD011279.pub2.
Williams ACC, Fisher E, Hearn L, Eccleston C. Psychological therapies for the management of chronic pain, excluding headache, in adults. Cochrane Database Syst Rev. 2020;8:CD007407. doi:10.1002/14651858.CD007407.pub4.
Australian Institute of Health and Welfare. International Classification of Diseases 11th Revision. Updated 5 March 2026.
Independent Health and Aged Care Pricing Authority. ICD‑10‑AM/ACHI/ACS Thirteenth Edition. Applicable to separations from 1 July 2025.
