The World Health Organization (WHO) has updated the International Classification of Diseases (ICD-11). For the first time, they have included chronic pain and provided specific pain diagnoses. Under the new system, chronic pain is classified as either chronic primary pain or chronic secondary pain.
Chronic primary pain is defined as pain that persists for longer than three months and is associated with significant emotional distress or functional disability and that cannot be explained by another chronic condition. This new definition applies to chronic pain syndromes that are best conceived as health conditions in their own right. Examples of chronic primary pain conditions include fibromyalgia, complex regional pain syndrome, chronic migraine, irritable bowel syndrome and non-specific low-back pain.
Chronic secondary pain syndromes are defined as pain that may initially be regarded as a symptom of other diseases having said disease being the underlying cause. However, a diagnosis of chronic secondary pain marks the stage when the chronic pain becomes a problem in its own right. In many cases, the chronic pain may continue beyond successful treatment of the initial cause; in such cases, the pain diagnosis will remain, even after the diagnosis of the underlying disease is no longer relevant. Examples of chronic secondary pain are chronic pain related to cancer, surgery, injury, internal disease, disease in the muscles, bones or joints, headaches or nerve damage.
More detail can be found in the online edition of Pain: The Journal of the International Association for the Study of Pain: