What Causes Itchy Arms?
Medical science is getting closer to understanding one of the most common causes of chronically itchy arms called brachioradial pruritus. This means we're also getting closer to helping people who suffer from this extremely frustrating condition!
A new study exploring the cause of brachioradial pruritus was just reported in the October issue of the Journal of the American Academy of Dermatology. The authors used MRI imaging to look at the cervical spine of 41 patients suffering from chronic itching of what was otherwise normal-appearing skin on the outer surface of their forearms arms (called brachioradial pruritus). MRI imaging showed a very strong correlation between the itch and nerve compression in the patient’s neck. In fact, the exact site of the itch on the skin correlated precisely with the spinal location in the neck where the nerve resides that supplies that part of the arm skin (we call this a dermatome*).
What’s so interesting is that the only sign of the nerve compression in the spine was the itchy skin "downstream" in the exact nerve root dermatome of the spinal nerve that was compressed. When we think of nerve root compression in the spine we expect pain, numbness, decreased muscle strength, and many more symptoms to be present, not just itch. These patients, however, did not have neck pain or other signs that we doctors would associate with spinal disease; they just had itchy skin "downstream" from the nerve!
We already knew that severe spinal diseases (disk herniation, spinal tumors, etc.) can result in an itch that’s seen in the "downstream" dermatome of skin supplied by that spinal nerve, but it also includes a host of other symptoms (pain, numbness, paralysis, etc.). Now we are finding that even subtle nerve root compression can cause just this vexing itch without all of the other symptoms. We’re still not sure exactly why the itch happens in a compressed nerve because the itch nerves are usually quiet unless something is tickling or biting the skin.
The authors of the study speculate that the slight compression may be making the itch nerves "hyper-excitable." They point out that the dermatome of skin with the subtly compressed nerve has altered sensory perception to pinprick and temperature, suggesting that the nerves really are "tweaked" by the compression.
What else did we learn about the arm itch (brachioradial pruritus) from the 41 patients studied?
- In every patient, a skin biopsy showed completely normal skin, confirming that the itch was not due to a skin problem. They did see changes common to chronically scratched skin (leathering, callous-like lesions, and scratch marks), but no rashes or skin problems that could cause itch.
- There was often burning and stinging sensations at the site as well as itch.
- The itch got worse with warmth and heat. (This is interesting because for years we've known that brachioradial pruritus is often worse in the summer. We attributed it to sun exposure, but perhaps the real trigger is heat.)
- The itch was improved by applying something cold (e.g. an ice pack).
- The itch often started in the dermatome of the nerve that exits the spine at cervical (neck) vertebra #6. (This nerve root supplies the outside surface of the forearms, over the brachioradial muscle, called dermatome C6.) Over time, the itch often grew to several adjacent dermatomes and the spinal issues and nerve root compressions were found in those dermatomes too when that happened.
- In most people, the itch was constant 24/7, but in some it, occurred intermittently.
- In about half of the patients, it was on both arms.
- In about half of the patients, the itch was worsened by touch, pressure, or scratching.
What can you do if you have itchy arms?
Talk to your doctor. Take this information to him or her and ask if it might fit your situation.
Keep your arms cool. Heat seems to make the itch worse.
Keep your arms out of the sun because for years patients have told us that sun exposure brings on the itch. This would mean wearing a sun-protective long sleeved shirt and/or zinc oxide sunscreen since these are the coolest ways to keep the sun off of your skin. Remember, chemical sunscreens generate a little heat when the sun hits them and zinc oxide sunscreens don’t. My favorite zinc oxide sunscreen for arms is Solbar Zinc.
Keep your arm skin well hydrated and free of scaly, flaky-skin! We think these troubled nerves are hyper-excitable and dry skin that’s got a fine covering of dry flaky scales will act like little tickling feathers when clothing or air cause the scale to move. My favorite regular skin care treatment to keep skin hydrated and scale-free when it's suffering from one of these neurogenic itch syndromes (like brachioradial pruritus) is my Anti-Aging Body Skin Care Kit. Spine disease and nerve compression are more likely to happen as we age, as is dry flaky skin. It's a perfect storm, but combining exfoliative hydrating skin care with my Body Kit helps. Another option is AmLactin Cream applied immediately after exiting the bath/shower and toweling dry (within 3 minutes) combined with the use of exfoliating bath mitt and very mild soap in the shower to exfoliate the skin.
How can you treat your itchy arms once the itch has started?
Slap on an ice pack! It’s the single biggest way to quiet down the itch because your nerves can only send out so many messages and when they’re screaming at you that the skin is cold, they can’t also keep sending you the message of itch.
Apply skin anti-itch products with pramoxine (such as Prax Lotion or Sarna Sensitive Lotion) or cooling itch creams with menthol and/or camphor (Sarna Original or Eucerin Itch-Relief Spray). Even better is to keep these products in the fridge so that they’re cold when you apply them.
Don't scratch, it makes the itch worse, plus it thickens, leathers-up, and damages your skin. It also causes your skin nerves to enlarge, which we can see under the microscope when we biopsy skin that's chronically rubbed and scratched. You don't need your skin nerves to be any bigger than they already are, so you've got to find some other way to respond to your itching, I suggest that ice pack.
The application of capsaicin cream topically to the itchy area of skin has been shown to help, but can cause stinging and irritation on sensitive skin.
Be sure to avoid anti-itch products that contain diphenhydramine and benzocaine because people often become allergic to these medicines when they apply them on their skin. The allergy results in an itchy rash that will make your itchy arm problem worse.
If you’re not able to get sufficient relief with these measures, you may want to talk with your doctor about some of the more involved treatments that have been shown to relieve the chronic itch of brachioradial pruritus. These include “cervical spine manipulation, physiotherapy, or orthopedic treatment” according to the authors. (I’ve had patients whose dermatomal neurogenic itch syndrome was cured by spinal surgery, but they needed the surgery for symptoms well beyond itch.) An oral medicine called gabapentin also shows promise for the treatment of neurogenic itch syndromes such as brachioradial pruritus.
The good news is that the causes of the itchy arm syndrome called brachioradial pruritus are becoming better understood. This means that we're sure to get better and better treatments for the relief of this vexing neurogenic itch syndrome.
*A dermatome is the skin area supplied by a spinal nerve. Your skin is "wired" very precisely; a nerve exits the spine between 2 spinal vertebrae and travels to a very specific area of your skin. It travels to only one part of your skin and that's called a dermatome. We doctors can actually map dermatomes on the entire body that correlate with each of the spaces between your spinal vertebrae. The outer side of your forearm is usually supplied by nerves that come for the 6th intervertebral space in your neck.
Marziniak Martin, MD et. al., J Am Acad Dermatol 2011;65:756-62.
Photo: Thanks and gratitude to Ben Fredericson