Nociplastic pain criteria or recognition of central sensitization? Pain phenotyping in the past, present and future

Key points

1. 01Nociplastic pain was introduced by IASP in 2017 as a third mechanistic pain type alongside nociceptive and neuropathic pain
2. 02The 2021 IASP criteria classify pain as 'possible' or 'probable' nociplastic pain using a grading system absent from the 2014 criteria
3. 03A new mandatory requirement in the 2021 criteria is clinical evidence of pain hypersensitivity (allodynia) in the region of pain
4. 04The Central Sensitization Inventory (CSI), used in the 2014 criteria, maps closely onto the comorbidities required for probable nociplastic pain in 2021
5. 05No psychometric or clinimetric studies validating the 2021 IASP criteria in patient populations have been published yet

How it was conducted

Design

Narrative review comparing two sets of clinical criteria for central sensitization or nociplastic pain

Criteria compared

2014 clinical criteria for predominant central sensitization pain vs. 2021 IASP clinical criteria for nociplastic pain of the musculoskeletal system

Target condition

Chronic musculoskeletal pain of at least 3 months duration with a suspected central sensitization mechanism

Scope

Historical overview, head-to-head criterion comparison, and future research agenda

What they found

• The 2021 IASP criteria classify pain as 'possible nociplastic pain' when four mandatory criteria are met: pain duration at least 3 months, regional rather than discrete pain distribution, pain not entirely explained by nociceptive or neuropathic mechanisms, and clinical signs of evoked pain hypersensitivity in the region of pain
• Classification as 'probable nociplastic pain' requires the four mandatory criteria plus history of pain hypersensitivity in the region and at least one defined comorbidity (sensitivity to sound, light or odours; sleep disturbance with frequent nocturnal awakenings; fatigue; or cognitive problems)
• The 2014 criteria required disproportionate pain plus diffuse distribution and/or a CSI score of 40 or higher out of 100; the optional CSI threshold of 40/100 is replaced in 2021 by mandatory allodynia testing
• Three of the four symptoms identified by Smart et al. (2012) as differentiating central sensitization pain from nociceptive and neuropathic pain are included in the 2021 IASP criteria
• The CSI is available in 18 languages and its psychometric properties in non-specific non-cancer pain are described as well-established in the cited literature
• CSI items map directly onto all four comorbidity categories required for probable nociplastic pain in the 2021 IASP criteria (sensitivity to light/sound/odours, sleep, fatigue, cognition)

Limitations

• No reliability or validity studies on the 2021 IASP criteria have been conducted; the paper is expert narrative, not an empirical study
• Mandatory allodynia testing may not discriminate nociplastic pain from nociceptive or neuropathic pain because primary hyperalgesia also occurs in inflammatory and neuropathic pain
• The criteria do not accommodate sensory hypo-sensitivity, which may accompany some nociplastic pain presentations
• Both criterion sets apply only to musculoskeletal pain and are not validated for visceral pain phenotyping

Why it matters

For patients

People with long-standing widespread pain that doctors cannot explain by injury or nerve damage may now be more accurately classified as having nociplastic pain, which should lead to treatments targeting the central nervous system rather than the local joint or tissue.

For clinicians

The 2021 IASP grading system provides a more structured and defensible pathway for classifying nociplastic pain in clinical practice, with mandatory allodynia testing replacing the subjective 'disproportionate pain' criterion, though formal validation studies are still needed before confident clinical adoption.

For readers

This review maps the evolution from early central sensitization criteria to the current IASP nociplastic pain framework, making it a useful orientation for anyone entering research or practice in chronic pain phenotyping.