When Even a Light Touch Hurts

Even the brush of clothing hurts.

When people first hear this, most assume it is an exaggeration. The patients themselves doubt their own words. "Maybe I'm just being oversensitive."

It is not oversensitivity. Medicine has a name for this phenomenon. Allodynia — a state in which a stimulus that should not be painful is felt as pain. And it is a very real pain.

Why does something that shouldn't hurt, hurt?

The skin has several kinds of sensory nerves. Some nerves carry pain, others carry light touch. These signals are sorted once in the spinal cord before they travel up to the brain.

Normally, touch signals are conveyed as touch, and pain signals as pain, each separately.

But when pain signals keep coming up for a long time, a problem arises at the sorting stage in the spinal cord. The pain circuit becomes excessively sensitive, and it starts to read even the neighboring touch signals as pain.

• The circuit widens, so even a small stimulus is conveyed as large
• The boundary between pain and touch blurs
• Even after the injured place has healed, only the signal remains

In this state, painkillers do not work well. Painkillers usually calm the inflammation at the painful spot, but the problem is not at that spot — it is in the circuit that reads the signal.

But it is not a problem of the circuit alone

This state has a name — "central sensitization" — and nerve stabilizers are used for it. They help in many cases.

I look at one more thing. Why was that pain signal continually coming up in the first place?

For a circuit to become sensitized, there must be something that has been sending signals for a long time. As long as that source remains, calming only the circuit will soon let it come back.

The source can be away from where it hurts

Something matters here. There is no rule that the source stimulating the circuit sits where it hurts.

There is an experiment in which an acidic solution was put into the shin muscle and an unharmed ankle some distance away hurt. (When Treating the Painful Place Does Not Heal It) That study measured one more thing — that ankle had also become more sensitive to pressure. It means the source of the signal may not be where it hurts, and that the place where it hurts can itself become sensitized.

Only the conditions at one site had changed, yet the pain arose elsewhere, and that place grew sensitive.

That the tissue is genuinely altered is measured too. Comparing 71 people with chronic low back pain against 50 without, the sliding between fascial layers was about 20% lower in those with pain. It does not show on imaging, but the tissue has changed.

So I do not look only at the place with allodynia. A compressed spot, or a spot stiffened and no longer moving, can sit somewhat away, and when the signal from there continues for months the circuit in the spinal cord becomes sensitized. From a certain point, it begins to read even a light touch as pain.

So I approach it on two fronts

When I deal with allodynia, I look at two things at the same time.

First, I cut off the source of the signal.
I look for the spot where the nerve is compressed, where the pressure has risen, where things have hardened and stopped moving. It is usually somewhat away from where it hurts. If I do not release this, the circuit keeps being stimulated.

Second, I turn the sensitized circuit back.
This takes time. A nerve circuit can weaken just as it strengthened, but not overnight. It needs continuous input, and the experience of moving without pain must be inscribed back into the circuit.

Either one alone is not enough. Cut off only the source and the circuit remains; soothe only the circuit and the source stimulates it again.

About time

Allodynia did not arise overnight. So it does not resolve overnight either.

Recovery does not come in a straight line; it comes while going back and forth between better and worse. I look, together with the patient, at how much less bad the worse days have become rather than at the better days. If the troughs of the waves are getting shallower, the direction is right.

It is rare to heal all at once. The troughs beginning to grow shallower is the start.

It is not that you are oversensitive

Allodynia has many causes. Cases where the nerve itself is damaged, cases that remain after shingles, cases where the nerve has been harmed by diabetes, and cases where the cause is never found. I do not claim that finding a compressed spot explains all allodynia.

When needed, I first recommend a neurology consultation or detailed testing. There are certainly times when painkillers and nerve stabilizers are needed.

But to those who have been told "the tests are normal, yet even a light touch hurts," I want to say clearly at least this much: it is not a matter of oversensitivity. The signal is coming up from somewhere. I will look for that spot with you.

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References

• Injecting an acidic solution into muscle produced pain not only at that spot but at the ankle some distance away, and made that area more sensitive to pressure — Pain, 2008
• Comparing 71 people with chronic low back pain against 50 without, sliding between fascial layers was about 20% lower in those with pain — BMC Musculoskeletal Disorders, 2011

Written by Dr. Heo Ji-young (PhD in Korean Medicine Pathology, Kyung Hee University · former Research Professor of Herbology, Kyung Hee University)