Chronic pain: definitions and diagnosis

According to the International Association for the Study of Pain (IASP), chronic pain is defined as "pain that persists or recurs for longer than three months."71015 This distinguishes chronic pain (as that persisting beyond normal tissue healing time) from physiological, acute pain.16 As this timeframe can be difficult to quantify, and a clear trigger or injury is absent in many cases, a somewhat arbitrary cut-off period of three to six months was originally adopted by IASP in 1994.18 The most recent definition supported by IASP uses a cut-off time of more than three months 1017, which has been incorporated into the classification system implemented in 2019 in ICD-11. This approach, which subdivides chronic pain into chronic primary pain and chronic secondary pain syndromes, has been developed to improve the ease and accuracy of data recording.710 According to ICD-11, chronic primary pain conditions include a collection of syndromes such as fibromyalgia and chronic migraine, which are considered health conditions in their own right. In contrast, the pain in chronic secondary pain conditions initially manifests as the result of another condition - eg, rheumatoid arthritis or inflammatory bowel disease - but diagnosing chronic secondary pain marks the stage when the pain requires treatment in its own right. Although it can be challenging to disentangle chronic primary pain from chronic secondary pain (and they can coexist), this general shift towards acknowledging chronic pain in its own right can help clinicians and patients move on from a mindset of searching for a diagnosis to discussing long term management strategies.19 Here, we will focus on chronic primary pain (particularly chronic widespread and musculoskeletal pain), although many of the concepts may also apply to chronic secondary pain and much of the literature to date does not yet distinguish between these two subcategories of chronic pain.