The International Association for the Study of Pain (IASP) defines pain as an unpleasant sensory and emotional experience associated with actual or potential tissue damage. Put simply, it is the experience generated by our nervous system when it interprets that there is, or may be, a threat to our body.
This definition has brought about an important paradigm shift because it separates concepts that for a long time were considered virtually equivalent: pain and damage are not the same thing.
Although it is a universal experience, every human being experiences pain differently. This is because its perception is influenced by hormonal, immune, psychosocial, occupational and family-related factors; the condition of our tissues and physical fitness; the functioning of the nervous system; our expectations and previous experiences; and even what we know about pain and the way we receive and/or understand a diagnosis.
When faced with an injury or a potential threat, the nervous system integrates information coming from the tissues together with information provided by all these factors and unconsciously evaluates the relevance of the situation. Pain is the result of this process, not a simple reflection of existing damage. This is why, in response to the same physical stimulus, two people may experience very different kinds of pain or, indeed, the same person may experience different symptoms depending on the moment and the context.
For a long time, medicine interpreted pain from a much simpler perspective: if pain was present, there had to be an injury to explain it. When no injury could be identified through conventional tests, pain was often attributed exclusively to psychological factors. Although our understanding has advanced enormously, this view still persists in part of clinical practice. Many patients, particularly women, continue to see their experience questioned or minimised, and interpreted as a manifestation of anxiety, stress or emotional distress.
If there is no injury to explain my pain, why does it hurt?
The fact that an imaging test does not reveal an injury does not mean there is no biological alteration. In some types of persistent pain, the problem lies in the functioning of the nociceptive system itself, the network responsible for detecting and processing signals of potential danger.
Thanks to techniques currently used in research, we know that this system can change the way it functions and become excessively reactive. This is what we call sensitisation: alarm mechanisms are triggered more easily, amplify incoming signals and may even remain active when the initial threat has disappeared. In this situation, the resulting pain is no longer considered secondary but rather primary pain, because the injury, if one exists, no longer fully explains the painful experience.
So, how is primary pain diagnosed?
There is no specific test that can diagnose it. The process begins with something much more basic, but essential: a thorough medical history and physical examination. We need to understand how the pain started, how it has evolved, its characteristics and underlying mechanisms. Diagnosing primary pain is not about “finding nothing”; it is about recognising its specific features while first ruling out the possibility that a disease may explain part or all of the symptoms.
This new perspective has led Hospital Clínic Barcelona to evolve from a model focused mainly on fibromyalgia, the best-known example of primary pain, to become the first hospital-based Primary Chronic Pain Unit in Spain. This approach broadens the focus and places particular emphasis on the diagnostic process before treatment begins. The aim is to avoid underdiagnosis or incorrectly labelling a condition as fibromyalgia or primary pain when it is not, something that can affect both future care and prognosis. After all, a diagnosis should never prevent us from continuing to look for answers when something does not fit.
