Carpal tunnel syndrome: thinking outside the box (or wrist)

Carpal tunnel syndrome (CTS) is the most common entrapment neuropathy and is caused by compression of the median nerve at the wrist. The classical neurological textbook will tell you that the symptoms caused by carpal tunnel syndrome are localised to the typical median nerve innervation territory in the hand, which involves the first three and half of the forth finger. Fact is however, that up to 70% of patients with CTS have symptoms outside the typical median nerve territory (Caliandro, La Torre et al. 2006). How do these extraterritorial symptoms fit with the common belief that CTS is driven by peripheral mechanisms?

There is a growing body of research demonstrating that patients with CTS have a generalised disturbance of somatosensory function (de la Llave-Rincon, Fernandez-de-Las-Penas et al. 2009; Zanette, Cacciatori et al. 2010). This theory is based on the finding that patients with CTS experience pain earlier than healthy people when thermal or mechanical stimuli are applied in areas that are not related to the median nerve (e.g. over the arm and neck). A generalised disturbance of somatosensory function in CTS would indeed explain the presence of widespread symptoms. Unfortunately though, most studies so far have not considered an important point. Many patients with CTS namely also have coexisting neck and/or arm pain. It therefore remains unclear whether the identified altered pain thresholds are truly caused by CTS, or are just a result of the coexisting neck or arm disorders.

To address this issue, we investigated whether the presence of abnormal extraterritorial pain thresholds can be substantiated in patients with CTS if coexisting neck and arm disorders are strictly excluded (Schmid, Soon et al. 2012). We could not replicate previous findings of abnormal pain thresholds in our patients who had symptoms localised to their affected hand. This suggests that CTS alone does not account for sensory changes outside the median nerve territory upon traditional quantitative sensory testing.  Interestingly though, our patients rated the pain elicited during pain threshold testing significantly higher than the healthy participants. This was not only apparent in the median nerve area of the affected hand, but also over the neck and the lower leg. Even though traditional quantitative sensory testing did not reveal any differences in pain thresholds, the elevated pain ratings in patients with CTS may still be an early indication of a generalised somatosensory disturbance. Our data further confirms that it is about time to start thinking outside the wrist in patients with CTS!

About Annina Schmid

Annina Schmid Neuroscientist University of QueenslandAnnina Schmid has recently completed a PhD in Neuroscience at The University of Queensland in Brisbane, Australia and works currently as a postdoctoral fellow at the same Institution. Her thesis is entitled “Implications of mild peripheral nerve compression beyond the lesion site. Mechanisms and Interventions”. The physiology of neuropathic pain is her main fascination and she endeavours to further unravel the mechanisms underlying peripheral compression neuropathies by using the animal model that she developed during her PhD as well as by translating findings directly to patients with compression neuropathies.

References

Caliandro P, La Torre G, Aprile I, Pazzaglia C, Commodari I, Tonali P, & Padua L (2006). Distribution of paresthesias in Carpal Tunnel Syndrome reflects the degree of nerve damage at wrist. Clinical neurophysiology, 117 (1), 228-31 PMID: 16325467

Llave-Rincón, A., Fernández-de-las-Peñas, C., Fernández-Carnero, J., Padua, L., Arendt-Nielsen, L., & Pareja, J. (2009). Bilateral hand/wrist heat and cold hyperalgesia, but not hypoesthesia, in unilateral carpal tunnel syndrome Experimental Brain Research, 198 (4), 455-463 DOI: 10.1007/s00221-009-1941-z

Schmid, A., Soon, B., Wasner, G., & Coppieters, M. (2012). Can widespread hypersensitivity in carpal tunnel syndrome be substantiated if neck and arm pain are absent? European Journal of Pain, 16 (2), 217-228 DOI: 10.1016/j.ejpain.2011.06.003

Zanette, G., Cacciatori, C., & Tamburin, S. (2010). Central sensitization in carpal tunnel syndrome with extraterritorial spread of sensory symptoms PAIN, 148 (2), 227-236 DOI: 10.1016/j.pain.2009.10.025

Comments

  1. Thank you for this very interesting article.
    The relationship between neck pain and carpal tunnel is not surprising for me, colleagues of mine have done a study on cupping in CTS.
    They used a single traditional cupping treatment over the trapecius muscle and the CTS symptoms were significantly reduced (Michalsen et al. 2009, Journal of Pain).
    Thanks again.

  2. I have CTS on my left hand. It started some 2 years after starting to wear a conventional body powered prosthetic arm. The harness typically compresses the brachial plexus to a degree and in part. The hand would go numb mostly but not only in the Median nerve region. Not wearing the prosthetic for 3-4 days would be sufficient to make numbness subside and improve. After 1-2 weeks of prosthesis abstinence numbness would be mostly gone. Wearing it again would make CTS symptoms come back. So we developed a new shoulder cable mount point that does not compress the brachial plexus and things are better. A lot better. – Secondly a reason for my CTS symptoms seems to be repetitive action with my left hand, or, overuse. When I take it easy symptoms are zero or minimal. After doing garden work or after swimming a long stretched out 800m crawl with perfect water grab and high elbow (technicalities in crawl swimming) the hand may go numb as early as after 300m. If I do not stretch the arm all the way I can go 3 km without problems. – – Regarding pain level: I mentally trained to suppress my considerable permanent burning phantom pains. One effect is that when I lifted a 30kg table with broken tiles using left hand covered by glove and stump covered by sock, it turned out that the arm stump was not protected too well and suffered deep lacerations. They bled and took 10 days to heal – but I didn’t feel pain there. I also did not feel any particular sting when I disinfected it using some regular Merfen disinfectant which years back would cause me a burning sensation on any open injury. – Last year I had herpes zoster / shingles after a H1N1 pneumonia which I got in context of serious overtraining (10 days with 1-2 sets of 2h swim sprint training each without proper nutritional supplement of what one uses up there) – and I did not feel any particular pain from the shingles, I sure did not lose any sleep over it, and I did not suffer from (in its literal meaning) postherpetic pain – I had increased sensitivity that I could find out by touching the area and paying attention to it, sure, but I was at no time distracted or disturbed by any such pain. I did not take any pain killers for the shingles, my alcohol consumption is minimal and as mentioned I do a fair bit of sport mostly every day. In other words I do have a really high pain threshold and a constant high pain level at the same time. – – – The mechanism that my neurologist mentioned was called double crush injury. – – – Changing the prosthetic harness improved the situation a lot – and not at all wearing the prosthetic (I am now off the arm since January due to an ill fitting liner and because my dermatologist said for me not to wear it and because it does take the technicians ages, quite literally, to come up with the new socket stuff) made the CTS symptoms almost fully go away.

  3. somnath shinde says

    its really nice research

  4. I’m especially interested in your research. I believe I have a carpal tunnel type issue but in my pelvis (pudendal neuralgia) and its been 5 years now (I fell on concrete floor after my fitball burst). Your ‘generalised somatosensory disturbance’ is of great interest to me. I feel a great core disturbance. A thunderstorm can send a surge up my spine and have my legs feeling like they’re going to give from underneath me in seconds. Excessive activity has me twitching in other parts of my body. I truly believe my whole nervous system has had some damage done but no one really knows what’s going on.
    If I can be of any research help please let me know. My name links to my online story if you need to read more.
    Thanks for your research!

  5. Andrew Cook says

    Interesting point – it’s not a correlation I’ve looked for, but will keep my eye open in future cases I see

    I read a really useful carpal tunnel information leaflet some 15 years ago, that classified it into

    a) restriction to the cervical vertebrae – clinically, based on treatment results, this seems to account for about 90% of carpal tunnel cases

    b) “true” carpal tunnel, where the wrist is square rather than rectangular – don’t see many of these

    c) a major ion/water imbalance causing local tissue odema in the wrist – again, don’t see many of these either

    The only truly repetitive wrist strain injuries I’ve ever seen were (i) an employee at a major news agency who was hitting about 100,000 keystrokes a shift, and (ii) a local office who had bought shishi glass tables which were the wrong height, and with no padding or thermal protection for the wrists.