The Mystery of Pain

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Friday, Sep. 08, 2006

The Mystery of Pain

Why does the same joint problem make one person suffer terribly

while another has no pain at all? There are a few clues that might

solve this puzzle

By DR. SCOTT HAIG

My patient Bob has a " bone-on-bone " knee — no cartilage at all

between his femur (thigh bone) and his tibia (leg bone). Common

arthritis looks white on an on X-ray; Bob's X-ray is a snowstorm.

He's as bow-legged as a cowboy, the inside of his bones have ground

each other down. Although his cartilage is all gone, there's

something even more important missing in his case. He has no pain.

Bob, 70, actually comes in this time because he has pulled a muscle.

When I examine him, I'm careful not to go on too much about the

arthritis. After a couple of weeks, he's back to normal. I've seen

him for over a decade with those same knees. He's still as active as

ever — plays tennis twice a week, with muscle pains and sciatica

once in a while.

What a contrast to my next patient. is half Bob's age. He

weighs less, isn't as active, and has nice straight legs. Barely a

trace of arthritis on X-ray and nothing except " minimal arthritic

changes " on his MRI. He has taken Advil, Naprosyn, Voltaren,

Celebrex with minimal help. Injections into his knees of hyaluronic

acid (a component of joint fluid) and corticosteroids provided only

a few weeks of relief. Physical therapy, braces, acupuncture, yoga

all failed. He couldn't get out of chairs, couldn't climb stairs

because of the pain. There was one thing left — a knee replacement —

and it worked. But we hate to do these for patients so young (35)

because we know that one way or another they're going to wear it out

and the re-do situation is very difficult.

Rotator cuff tears, herniated discs, torn knee ligaments and

cartilages are just like this; the same abnormality that hurts some

folks doesn't hurt others. Over 80% of asymptomatic adult volunteers

(people with no pain at all) who let us do an MRI of their necks

were found to have abnormalities — like disc herniations and bone

spurs — that we commonly operate on in symptomatic patients. The

rotator cuff, my particular expertise, is even more mysterious. When

it's torn and symptomatic, there is measurable weakness. A big,

symptomatic tear often makes it impossible even to raise one's arm

to eye level, and this doesn't get better until you fix it. But then

you have patients with asymptomatic tears — and they can be really

big tears — who not only are pain free but have strong shoulders

with full motion as well.

Why does the same problem hurt one person and not the next? Here is

the greatest mystery of my profession. As doctors, especially in my

field of orthopedic surgery, we like to act as if we understand

things like this — but we don't. It's a really interesting question

because whoever answers it can turn a into a Bob — getting the

pain to go away without doing the operation — and this would be a

minor miracle. We do have some tantalizing tips, though, about what

makes things hurt.

The first is inflammation. An object lesson here was taught by an

old drug. Those older than 50 might remember Zomax. It was an anti-

inflammatory that was also an amazing pain reliever. I was just a

medical student when it was pulled off the market because of side

effects, but I clearly remember patients with broken legs or fresh

post-ops who were treated for pain with Zomax alone. They were

nearly pain-free and clear as a bell with no narcotic drowsiness.

This " super Advil " worked along the same chemical pathways as all

the other non-steroidal anti-inflammatory drugs — just better. And

it seemed to take away arthritis pain almost completely, making

symptomatic cases asymptomatic for eight hours at least.

We are quite familiar with the pain-inflammation connection. The

most powerful anti-inflammatory drugs we have are the

corticosteroids like prednisone. They have too many side effects to

be first-line arthritis drugs but many folks have to take them for

other reasons. These patients might find them actually too effective

against pain. Appendicitis, gall bladder disease or even bowel

infarctions can occur in these patients without them feeling any

pain at all. This is very dangerous — the pain of early appendicitis

is a good thing; it saves lives by bringing patients to the doctor

before they start to die of abdominal infection.

The biochemistry of the inflammatory process, which we recognize by

an increase in local blood flow (more blood equals more heat equals

inflammation) creates, among other things, molecules that sensitize

pain-associated nerve endings. This process is very complicated but

it's a good bet that sooner or later safe anti-inflammatory drugs

will solve most of the pain problem. I, for one, am looking forward

to a safer version of Zomax — both for my patients' sake and, in my

creaking dotage, my own.

Neural blockade — control of the various " gateways " through which

pain signals reach our brains, is next. There' s no doubt that pain

is ultimately a mental phenomenon whose survival value involves some

kind of negative re-enforcement; we learn not to hammer our thumbs

by punishing experience. There are times when there' s more survival

value in not feeling pain though, and at those times, even injured,

we often don't have pain. Anyone who has seen an action movie knows

we can take quite a beating yet be oblivious to pain. This is neural

blockade at the highest level — in the brain. But it can happen all

the way down to the nerve-ending level. There is a well-known pain

gate in the spinal cord; regional anesthesia controls pain by

temporarily blocking nerve transmission via chemicals injected

around more peripheral nerves. Farther down toward the pain-

associated nerve endings we create neural blockade with topical

anesthetics (like what the dentist puts on your gum so you don't

feel the novocaine needle) or even ice.

As an orthopedist who has seen a lot of tough older men with

painless, yet arthritic joints, I'm suspicious of there being a

peripheral pain blockade that sometimes occurs around joints that

are simply not given a chance to rest when they hurt. These are the

ones who when asked " Don't you have any pain? say something

like " not really but what does it matter, I still have to work to

put the food on the table. " I don't think it can be a central

blockade because it's always there; mental or brain level

suppression would be more variable.

That the mind could produce a physical change in the peripheral

nerves is not impossible, however. With my own eyes I have seen the

red circle left by an ordinary quarter, on the arm of a fellow

student under hypnosis in medical school. I told her it was a

burning coal but that she couldn't move to take it off. We thought

her grimacing seemed a little fake. But the very obvious

inflammation of the skin touching the quarter was not. It showed

that the brain's control of specific, tiny nerves — in this case the

tiny blood vessels in the skin — is profound.

Finally, depression and hormones have a lot to do with pain in some

people. Back and neck pain flare-ups in people under stress are

commonplace. We have successfully treated many pain patients with

anti-depressants. Back in the days of female hormone replacement

therapy, samples of estrogen skin patches gave great relief of all

sorts of joint pains suffered by certain peri-menopausal patients.

Exercise, strangely enough, seems to have taken the place of the

hormones we used to give — with nearly the same pain relief. This

might be a covert form of hormonal therapy itself; the " pleasure

hormones " or endorphins that are released in the brain by exercise

(and eating and sex too) are potent natural pain killers.

So we clearly have some leads; in 20 years we'll probably understand

it, but today pain remains a tantalizing mystery. For now if you

want to avoid that knee replacement, the best I can recommend is

that you is cheer up, pop an Advil, keep working, go to the gym, eat

something and buy your spouse a present.