I've attached my own commentary.

<http://www.webmd.com/content/article/131/118210?src=RSS_PUBLIC>

February 18, 2007

Study Shows Stronger Link to Genetics Than Excessive Typing or Hand Use
By Kathleen Doheny
WebMD Medical News   Reviewed By Louise Chang, MD
on Friday, February 16, 2007

Feb. 16, 2007 -- Long hours surfing the Internet or typing won't wreck
your wrists, a new study shows.

Carpal tunnel syndromeCarpal tunnel syndrome, long associated with
overuse of the hands and wrists when surfing the Internet or typing, is
linked more to genetics than repetitive use, according to the study.

It was presented today at the 74th Annual Meeting of the American
Academy of Orthopaedic Surgeons in San Diego.

"The link between carpal tunnel syndrome and hand use is overstated and
may be inaccurate," says study researcher David Ring, MD. Ring is an
assistant professor of orthopaedic surgery at Harvard Medical School and
a hand surgeon at Massachusetts General Hospital, Boston.

"The scientific support for the concept [that carpal tunnel is caused by
overuse] is, on average, relatively weak," he says. "The major risk
factor for carpal tunnel is genetic."

Exactly what those genetic factors are is not known, he says, but they
may be related to the structure of the hand and wrists.

What Is Carpal Tunnel Syndrome?

In carpal tunnel syndrome, the median nerve, running from the arm into
the hand, becomes pressed or squeezed at the wrist.

This nerve controls sensations to the thumb's palm side and part of all
the fingers except the little finger.

When the median nerve is squeezed, there can be tingling, pain,
weakness, or numbness in the wrist and hand that radiates up the arm.

Treatment options include rest, immobilization of the wrist, and surgery
to reduce pressure on the nerve.

"A common perception is that carpal tunnel is related to hand use," Ring
says.

That perception is more common among consumers, he says, but some
doctors also believe it.

Studies on whether carpal tunnel syndrome is associated with hand use
have been mixed.

Carpal Tunnel vs. Repetitive Strain Injury

Ring differentiates between carpal tunnel syndrome and repetitive strain
injury, which he prefers to call idiopathic (cause unknown) arm pain.

In this condition, he says, there is pain "but no evidence of injury. It
doesn't involve the carpal tunnel."

The Study

To clarify the debate, Ring and his colleagues looked at 117 studies on
carpal tunnel syndrome published in the medical literature.

They used scientific criteria that determines the strength of a
cause-and-effect relationship by giving it a score.

The researchers looked at biological factors -- such as genetics -- and
occupational factors -- such as a person's job or the amount of
repetitive hand use.

After analyzing the studies, "The quality and strength of evidence
supporting genetic or inherent risk factors was felt to be moderate,"
Ring says.

"The quality and strength of evidence supporting occupational risk
factors was felt to be poor," he says.

Average scores for biological factors linked to carpal tunnel syndrome
were double those of occupational factors, such as occupation or
repetitive hand use, Ring reports.

Implications of the Study

"The link to genetics is strong and believable," Ring says. "If you are
diagnosed with carpal tunnel, you are an innocent bystander. You did
nothing to cause it."

"This should give reassurance to those who use their hands a lot," he
says.
------------------------------------------------------------------------

SOURCES: David Ring, MD, assistant professor of orthopaedic surgery,
Harvard Medical School; hand and upper extremity surgeon, Massachusetts
General Hospital, Boston. 74th Annual Meeting of the American Academy of
Orthopaedic Surgeons, San Diego, Feb. 16, 2007.

------------------------------------------------------------------------

Carpal tunnel can be a symptom of any number of stressful conditions
which affect peripheral nerves, ranging from diabetes to metals
poisoning.  A severe enough food allergy or magnesium deficiency can
cause muscle spasms which compress various neurovascular bundles leading
to carpal tunnel pain.  You may not evern feel anything in the area of
compression.  A good physical therapist may be able to sort this out for
you.

Other causes of carpal tunnel pain can include B vitamin or other
nutritional deficiency, autoimmunity (especially an inflammatory bowel
problem), pregnancy, growth hormone or sex steroid deficiency, TMJ/TMD,
fungal infection and obesity.  Generally speaking, you would probably
see other symptoms but they might appear minor (e.g., athlete's foot,
sinus infections or split fingernails).

Some of these causes can overlap and interrelate.  The bottom line is
they would lower your natural pain threshold in some fashion.  Women
tend to be more sensitive to pain than men - except redheads, who have a
mutation in the neuropeptide system - so it's no surprise women tend to
report more upper body neuromuscular pain.*  Men may be protected by our
naturally higher carnitine levels (testosterone is a carnitine
transporter).  It tends to be the case that taking carnitine raises the
pain threshold while a carnitine deficiency lowers it.  Carnitine
transport defects are associated with autoimmune conditions [PMID
17065219].  Acetyl-l-carnitine, in fact, is one of the few
over-the-counter substances which can repair damaged peripheral nerves
(although it can have side effects).

Substances which inhibit protein kinase C (DHEA, fish oils, a low
glycemic index diet) can boost the pain-relieving actions of carnitine
[PMID 15223307].  Similarly, substances which activate PKC would reduce
this effect and lower the pain threshold.  Sugar elevates PKC.  Wheat in
somebody with celiac disease can elevate PKC.  High homocysteine (i.e.,
a B vitamin deficit) elevates PKC.  Homocysteine also has a nasty habit
of blocking GABA receptors.  Even sleep apnea can raise PKC.

Pain can also be a reflection of opioid signaling problems.  Certain
autoimmune digestive disorders or even just chronic antibiotic use can
knock out mu opioid and cannabinoid receptors [PMID 17159985], which
means you've got fewer docking stations in nerve cells for your body's
own natural analgesics.  Sure enough, when this happens in mice their
tolerance of painful stimulus drops
<http://www.newscientist.com/article/dn10808.html>.  Low-dose naltrexone
can help reverse this alteration and that's probably one reason it's
highly effective for inflammatory bowel disease and Crohn's.  PKC is
also a factor here; it can decrease the number of opioid receptors [PMID
17000011].

It's easy to think this doesn't apply to you but red meat, cow's milk
(casein), wheat and rice digest into natural opioids.  When the gut
barrier is leaky, these partially digested allergens can pass into the
bloodstream and start screwing up your opioid receptors.

There are plenty of other things that matter to pain perception.  
Diabetes, for instance, has a habit of screwing up the body's inhibitory
signaling system (GABA receptors).  I bring up carnitine and opioids
because the research is very recent and most physicians probably haven't
heard of the links.  Discussing this also gives you an idea of how
important various aspects of your metabolism are to pain perception.

Unfortunately, most orthopedists are not competent in these areas of
medicine.  When you're a hammer you tend to see the world as filled with
nails.  Surgeons are no different.  They tend to see the world as filled
with surgical problems.  Indeed, a lot of doctors seem to totally forget
the Krebs cycle once they get out of med school.  Finding one who will
be thorough can be difficult.

I don't know if carpal tunnel surgery is appropriate for any given
individual.  You'll have to make this determination yourself.  I hope
this gives you an idea of how complicated your health problems could
really be once the symptom appears.  Also remember that American
medicine hasn't yet heard of statistical quality control.  We spend more
time and effort figuring out what movies you like to rent than we do
figuring out medical mysteries.  

*  There's also a gender difference in the ability to cause pain as
well.  A female shot nurse will, all other factors being equal, inflict
slightly less pain on her patients because of the way the brain's
perception systems work.