You're In Chronic Pain: Exactly What Sort Of Pain Is That?

Today's post from painscience.com (see link below) follows on from yesterday's video about types of nerve and nerve damage by looking more closely at the pain this damage causes. One of the reasons why pain is so difficult to treat (apart from the scale of damage to the nerves) is that there are also differing types of pain which demand different approaches. Apart from that, there are other forms of pain that are very difficult to classify and therefore even more difficult to treat. Little wonder then that science is having so much trouble in finding suitable treatments for pain related diseases - especially neuropathic pain. The fact that it relies on a list of medications meant for other conditions and that list is pretty much unchanged since the 2nd World War, says enough. Finding appropriate and successful treatments for nerve damage pain is one of the greatest challenges facing the medical community and progress is literally...painfully slow! This article is important knowledge for neuropathy sufferers who aren't sure what sort of pain they have and is definitely worth a read.

The Basic Types of Pain: Nociceptive, neuropathic, and “other”
by Paul Ingraham, Vancouver, Canada  updated Jul 12, 2017

There are two well-recognized broad categories of pain: the common sensical sort (the pain of damage), and the somewhat more exotic kind that comes from damage to the system that reports and interprets damage, the nervous system. It’s the difference between engine trouble and trouble with that light on your dashboard that says there’s engine trouble.

More specifically:
 
Nociceptive pain arises from various kinds of trouble in tissues, reported to the brain by the nervous system.1 This is the type of pain everyone is most familiar with, everything from bee stings and burns and toe stubs to repetitive strain injury, nausea, tumours, and inflammatory arthritis. Nociceptive pain typically changes with movement, position, and load.

Neuropathic pain arises from damage to the nervous system itself, central or peripheral, either from disease, injury, or pinching.2 The simplest neuropathies are mechanical insults, like hitting your funny bone or sciatica, but this is a big category: anything that damages neurons, from multiple sclerosis to chemotherapy to alcoholism to phantom limb pain. It’s often stabbing, electrical, or burning, but nearly any quality of pain is possible. Unfortunately, it’s also more likely to lead to chronic pain: nerves don’t heal well.3

Migraine? Still tough to classify! Some experts consider it a major category of its own, parallel to nociceptive and neuropathic pain,4 but it’s probably just a complicated neuropathy.5

Obviously these kinds of pain can overlap. Some medical problems, like injuries, can affect both nerves themselves and other tissues, causing both kinds of pain. However, it’s surprising how little overlap there is: look at any list of the most painful conditions [NHS] and they all fit pretty clearly into one category or the other.

Pain is predictably unpredictable, thanks to brains. Regardless of type, all pain is weird in some typical ways, because it’s all under the total control of our brains,6 and brains have complicated and conflicting priorities for us that we are oblivious to.7 The result is that pain is often weird, a somewhat paranoid guess about how much danger we’re in, and that’s when everything’s working correctly. If the nervous system is damaged (neuropathic pain), then the brain is getting bad information, and pain gets even weirder. But when the nervous system misbehaves, pain can get so wonky that a whole new category of pain might be needed.


ZOOM

Although the different kinds of pain certainly can overlap, mercifully it’s relatively rare to end up in “hell” at the centre of this Venn diagram. Unfortunately, the “other” category often does arise from a history of other kinds of pain. 

File under “other”: pain problems for which we might need a new word

Some common kinds of pain are not a great fit for either of the two official categories. The canonical example is the pain of fibromyalgia. [Mayo] Other major examples:
complex regional pain syndrome (CRPS) [Mayo]
nonspecific chronic low-back pain
irritable bowel syndrome [Mayo] and other functional visceral pain disorders
conditions that begin as nociceptive pain, like osteoarthritis, but then go into a hellish downward spiral of sensitization8

Fibromyalgia is probably a pain system dysfunction, a poorly understood multi-system failure causing widespread body pain (and more9), but “dysfunction” of the nervous system is specifically excluded from neuropathic pain, by decree, as of 2011.10 Dysfunction means that fibromyalgia isn’t caused by any (known) damage to the nervous system, but by its misbehaviour, and so it’s not welcome at the neuropathy club. It was before 2011! But not anymore.

Maybe there are unknown lesions? Maybe someday we’ll know that fibromyalgia is caused by some kind of subtle damage to the nervous system.11 There are at least two theories of subtle lesions of this type.12 That would make it just another neuropathy after all, ho hum. But for now it’s still more plausible that it’s a dysfunction, arising from widespread problems in a complex system, and no clear point of failure will ever be discovered.1314 But who knows. Science is not finished with fibromyalgia.

Meanwhile, what do we call it? And other miserable pain problems that arise from what seem to be neurological dysfunction? 

Possible names for this other kind of pain

“Other” is a bit vague, so experts have proposed some more descriptive names for this category. There are issues with all of them. (The first three here all come from the same source.15)
Nocipathic pain: abnormal nociception. This is basically a fancy way of saying “other” pain, and I don’t think it adds much.
Nociplastic pain: like nocipathic, but a little more descriptive, implying specifically that the problem arises from changes in how nociceptive pain works.
Algopathic pain: pathological perception/sensation. This is the Greek way to say “pain disease.”
Centralized pain16 or maladaptive central processing17: pain driven by the spinal cord and brain, regardless of what’s going on in the tissues.

The “noci” terms seem a little misguided to me, because the pain of a misbehaving nervous system is so much closer kin to neuropathic pain.18 Centralization is an important concept and element, but clearly not the whole story19 (and “maladaptive” might be too blamey20). Algopathic gets my vote: suitably neutral and formal, while saying just enough to be better than “other.”
Do sensitization and centralization belong in the “other” category? Many of us experience normal, healthy centralized sensitization every time we go to the dentist, because our nervous system is not an idiot

Sensitization is the amplification of danger signalling in any part of the system (which can be driven by both peripheral and central neurology, while centralization is referring only to the latter). It seems like a slam dunk to put these in the “other” category, but not so fast: the nervous system is not being dysfunctional just because it overestimates some danger. Many of us experience normal, healthy centralized sensitization every time we go to the dentist, because our nervous system is not an idiot and is very suspicious of dentists based on past experiences. Our brains think the dentist is a threat, and although they are technically wrong — the dentist is actually there to help — the judgement is not “dysfunctional.”

Sensitization is clearly part of the normal function of the pain system — it’ s not a dumb system where pain is always exactly proportionate to tissue danger. It’s more subtle. Sensitization/centralization is only dysfunctional when it’s chronic and seriously disproportionate. And of course there’s a grey zone a mile wide between normal and dysfuntional. It’s a spectrum.

File under “unknown”: pain problems that can’t be categorized yet

Sometimes we just don’t understand a problem well enough to classify it. The best example of this is the sensitive spots in soft tissue that so many people have — “trigger points,” the things that motivate most massage therapy appointments. There is a popular hypothesis that they are caused by a problem with muscle tissue, which would make it a clear case of nociceptive pain from a fairly subtle lesion… but it’s just an hypothesis, and some experts have suggested that trigger points are caused by a problem with nerves themselves, which would make them neuropathic.21 No one actually knows, and it’s not likely to be settled for a long time. 

Article Summary

There are two main classifications of pain: the common sensical sort that arises from damaged tissue (nociceptive pain), and the more exotic kind that comes from damage to the system that reports and interprets damage, the nervous system (neuropathic pain). This is the difference between engine trouble and trouble with that light on your dashboard that claims there’s engine trouble. Oddly, there is still no official “other” category for the pain of conditions like fibromyalgia and irritable bowel syndrome, which involve dysfunction of the nervous system, as opposed to damage; names like nocipathic or algopathic are on the table.

https://www.painscience.com/articles/pain-types.php