鈥淧AIN yearns to be communicated,鈥� says Haider Warraich at Brigham and Women鈥檚 Hospital, Massachusetts. Instinct makes us yell when we are hurt, and communicating pain is often described as a therapy itself 鈥� even screaming a swear word or two after stubbing your toe seems to soothe the agony. And yet modern medicine flounders when it comes to interpreting a person鈥檚 pain. More often than not, it attempts to compress the physical and emotional complexity that contributes to the experience of pain into a single figure on a pain intensity rating.
That is problematic, says at McGill University in Canada, not least because rating your pain between 0 (none) and 10 (the worst imaginable) is intrinsically subjective.
One alternative is qualitative sensing testing, where you apply stimuli and ask the individual to indicate when they start to feel it, when it feels uncomfortable and when to stop. Mogil says this allows you to compare an individual鈥檚 general experience of pain against the average, but says little about the pain that person is experiencing in the moment.
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Another option is the . First published in 1975, it suggests 78 descriptors for pain, from 鈥渟earing鈥� to 鈥渁nnoying鈥� and 鈥渂linding鈥�. A person chooses a number of words, each of which has an associated score that can be tallied. The individual also indicates the parts of the body experiencing pain and gives an intensity rating. Despite its subjectivity, Mogil says it is the intensity rating in the questionnaire that tends to get used the most.
Many researchers believe a more objective measure is needed. They are working on systems that go beyond self-reporting, attempting to find biological signals, such as pulse rates, sleep patterns or even brain activity, that could help to determine the type and intensity of a person鈥檚 pain.
Progress has been made, says , a neuroscientist at the University of Oxford. For instance, brain scans reveal a difference in the 鈥� the opioid tramadol and pregabalin 鈥� which the person鈥檚 own pain-rating scores don鈥檛 reflect. You might wonder what good that is if the person taking the drug isn鈥檛 feeling the benefit. But these insights are helping to piece together the extent to which different factors contribute to the experience of pain, all of which can point to different treatments, says Tracey, who described the experiment at the in New York earlier this year.
For example, anxiety and depression can worsen a person鈥檚 experience of pain, dull the efficacy of opioids and heighten the risk of chronic pain (see 鈥淲hy emotions can feel so painful 鈥� and what it means for painkillers 鈥�). The strength of social support networks and also feed into how a person feels and working out the best way to treat them. If a person鈥檚 brain activity suggests they are responding well to a pain-relief drug, yet they are still feeling pain, it may be that one of the other elements is the predominant factor influencing their overall experience.
Artificial intelligence can also help by analysing multiple pain metrics. have embraced this approach with a that began by recording 34 different metrics from 1700 individuals experiencing chronic pain. Pairing Boston Scientific鈥檚 expertise in measurements with IBM鈥檚 strength in machine learning, a team of researchers whittled these down to just seven types of useful data, which combine 12 of the original 34 metrics. Many of these can be recorded with a smartwatch and are a combination of self-reports on mood, alertness, sleep and so on, as well as objective measures, such as mobility.
The project uses AI to assess an individual鈥檚 pain and predict how it will evolve, allowing personalised, pre-emptive interventions. To demonstrate its effectiveness, researchers enrolled 76 people who were using spinal stimulators to manage chronic lower back or leg pain. For the first 30 days of the trial, participants followed their usual stimulation programme, which was based on standard recommendations. For the next 30 days, an AI analysed their metrics and gave daily recommendations for what stimulation programme to use. Participants recorded their pain intensity and the quantity of opioids used daily. At the end of the trial, 84 per cent of participants showed a significant improvement in pain experienced and quality of life with the AI recommendations.
For now, this approach still uses self-reported pain intensity scores in conjunction with biological measures. Ultimately, retaining an element of self-reporting may not be a bad thing, so long as the complexity of the pain experienced and its impact on quality of life is recognised. After all, 鈥減ain is subjective鈥�, says Warraich. 鈥淪ubjective experiences are really at the heart of what makes us human.鈥�
Painful prejudices
It is a sorry fact: a woman鈥檚 experience of pain is more likely to be dismissed than a man鈥檚. This 鈥済ender pain gap鈥� is reflected in longer waiting times in emergency departments, a greater incidence of and a lower likelihood of at all. An exacerbating issue is the different mechanisms by which cisgender women and girls and transgender men experience pain through the activation of T cells 鈥� as opposed to the microglial cells activated in the spinal cord of cisgender men and boys and transgender women 鈥� which makes them more sensitive to painful stimuli. This has only come to light over the past 20 years because clinical studies were historically biased towards using male animals. Recent research also suggests transgender and cisgender women have a higher pain sensitivity compared with cisgender men, highlighting the importance of gender identity.
Other biases play into pain assessment too. Haider Warraich at Brigham and Women鈥檚 Hospital in Massachusetts says someone鈥檚 attractiveness, skin colour, language and socioeconomic status can all affect how and when pain is treated. 鈥淭hese all come to affect the person in pain, perhaps more than any other patient who seeks medical care,鈥� he says. He highlights a US study on appendicitis, a well-understood condition with straightforward tests and treatment, which involved children. 鈥淢y thought was we might have a kinder, gentler approach to children,鈥� says Warraich. Nevertheless, as a standard pain relief treatment compared with white children.
This story is part of a special feature on pain in which we explore:
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What is pain, how does it work and what happens when it goes wrong?
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Viewing chronic pain as its own illness is providing better treatments
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We are only just beginning to understand what causes nociplastic pain
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The new pain treatments that may finally stem the need for opioids
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Why emotions can feel so painful 鈥� and what it means for painkillers
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