DermHelpCentral

The Neurology of Itch

The neurology of itch.
Dhand A1, Aminoff MJ. Brain. 2014 Feb;137(Pt 2):313-22
Abstract: Research over the past 15 years has helped to clarify the anatomy and physiology of itch, the clinical features of neuropathic itch syndromes and the scientific underpinning of effective treatments. Two itch-sensitive pathways exist: a histamine-stimulated pathway that uses mechanically insensitive C-fibres, and a cowhage-stimulated pathway primarily involving polymodal C-fibres. Interactions with pain continue to be central to explaining various aspects of itch. Certain spinal interneurons (Bhlhb5) inhibit itch pathways within the dorsal horn; they may represent mediators between noxious and pruritic pathways, and allow scratch to inhibit itch. In the brain, functional imaging studies reveal diffuse activation maps for itch that overlap, but not identically, with pain maps. Neuropathic itch syndromes are chronic itch states due to dysfunction of peripheral or central nervous system structures. The most recognized are postherpetic itch, brachioradial pruritus, trigeminal trophic syndrome, and ischaemic stroke-related itch. These disorders affect a patient's quality of life to a similar extent as neuropathic pain. Treatment of neuropathic itch focuses on behavioural interventions (e.g., skin protection) followed by stepwise trials of topical agents (e.g., capsaicin), antiepileptic drugs (e.g., gabapentin), injection of other agents (e.g., botulinum A toxin), and neurostimulation techniques (e.g., cutaneous field stimulation). The involved mechanisms of action include desensitization of nerve fibres (in the case of capsaicin) and postsynaptic blockade of calcium channels (for gabapentin). In the future, particular histamine receptors, protease pathway molecules, and vanilloids may serve as targets for novel antipruritic agents. Free Full Text.

Notalgia paresthetica

By Dr. Carolyn Ellis, Largo Medical Center, Largo, Florida

The 57 year-old woman pictured below has had episodic pruritus of the mid-back for six years.  She denied axny apparent cause for the pruritus.  At times there was an accompanying sensation of 'pins and needles'.   She also complained of heightened sensitivity in the area, which she noticed when putting on clothes or rubbing her back against the bed.  She located the affected area medial to the left scapula.  She could not identify anything that improved or worsened the symptoms.

Notalgia Paresthetica (NP) is an ecxeeding common disorder.  Dr. Carolyn Ellis has written a fine introduction to NP. See: Download NP edit

Typical Distribution of NP

Subtle Hyperpigmentation and Lichenification

 

Dr. Ellis' Teaching Points

 

CLICK IMAGE TO ENLARGE

 

 

An "Eczema" Story

In the Well section of the NY Times there is an excellent article on "Waking Up With Eczema" (December 25, 2011).  This essay will appeal to patients with "atopic dermatitis" as well as those who itch for other reasons.  There are well over a 100 comments, and some are very good, as well.  Itching, eczema, and atopic dermatitis are frustrating to live with and diffiuclt to treat.  This is a valuable introduction.

Itching in the Elderly

"The most common skin complaint in the elderly is pruritus. The multitude of variables that come with advanced age means that the management of pruritus in the elderly poses a particular therapeutic challenge. Pruritus in advanced age may result from a variety of etiologies, although xerosis is the most common. In addition, certain cutaneous and systemic diseases that are associated with pruritus are more prevalent in the elderly. At present, there is no universally accepted therapy for pruritus. Currently, management of pruritus in the elderly must take an individualistically tailored approach with consideration of the patient’s general health, the severity of symptoms, and the adverse effects of treatment. Physical and cognitive limitations, multiple comorbid conditions, and polypharmacy are some aspects that can influence the choice of treatment in this age group."

The above is the abstract for a good article: "Management of Chronic Pruritus in the Elderly."

Notalgia Paresthetica: Successful Treatment with Exercises

The authors describe here two cases in which the condition was improved by exercises involving non-pharmacologic active range of motion and strengthening of the scapular muscles as well as stretching of the pectoral muscles.  See full article: Download Notalgia Exercise

Here is a good Overview of Notalgia from Dermnet.

On Itch (Mark Twain)

Huckleberry Finn, Chapter 2

There was a place on my ankle that got to itching, but I dasn't scratch it; and then my ear begun to itch; and next my back, right between my shoulders. Seemed like I'd die if I couldn't scratch. Well, I've noticed that thing plenty times since. If you are with the quality, or at a funeral, or trying to go to sleep when you ain't sleepy--if you are anywheres where it won't do for you to scratch, why you will itch all over in upwards of a thousand places.

Pretty soon Jim says: "Say, who is you? Whar is you? Dog my cats ef I didn' hear sumf'n. Well, I know what I's gwyne to do: I's gwyne to set down here and listen tell I hears it agin." So he set down on the ground betwixt me and Tom. He leaned his back up against a tree, and stretched his legs out till one of them most touched one of mine.

My nose begun to itch. It itched till the tears come into my eyes. But I dasn't scratch. Then it begun to itch on the inside. Next I got to itching underneath. I didn't know how I was going to set still. This miserableness went on as much as six or seven minutes; but it seemed a sight longer than that. I was itching in eleven different places now. I reckoned I couldn't stand it more'n a minute longer, but I set my teeth hard and got ready to try.

Topical Steroid Potency Chart

 Topical steroid preparations are grouped according to relative anti-inflammatory activity, but activity may vary considerably depending upon the vehicle (cream, ointment, solution, foam, etc.), the site of application (face, skin folds and genitalia), disease, the individual patient and whether or not an occlusive dressing is used.  In addition,there are a number of these charts and they are not entirely consistent.  The National Psoriasis Foundation's Potency Chart is well-prepared and a good general guide.

Topical steroids should be used under your doctor's direction, since overuse can cause thinning of the skin, rosacea, acne, stretch marks if used on the wrong part of the body and for too long.  .

Itch - Update

From the NY Times, April 7, 2009 (Health Section)

Scratching Relieves Itch by Quieting Nerve Cells

By Benedict Carey

A new study "reports that specialized cells in the spinal cord appear to be critically involved in producing the sensation of itch and the feeling of relief after the application of fingernails, at least in healthy individuals. The study appears in the current issue of the journal Nature Neuroscience.

It suggests that itch, like pain, may be a “gated” system in which signals from other nerve cells can interfere with or moderate the sensation. Scratching the skin near, but not directly on, the spot that itches often provides relief, just as rubbing an aching limb can reduce pain. Perceptions in the brain, too, probably moderate the urge to scratch: some chronic, compulsive cases of itching suggest that the brain is not properly reading the effect of outside signals at all but is instead acting on a mistaken internal representation of what is happening to the skin.

Full NY Times Article

Nature/Neduroscience Article:

Davidson S, Zhang X, Khasabov SG, Simone DA, Giesler GJ Jr. Relief of itch by scratching: state-dependent inhibition of primate spinothalamic tract neurons.

Itch is relieved by scratching, but the neural mechanisms that are responsible for this are unknown. Spinothalamic tract (STT) neurons respond to itch-producing agents and transmit pruritic information to the brain. We observed that scratching the cutaneous receptive field of primate STT neurons produced inhibition during histamine-evoked activity but not during spontaneous activity or activity evoked by a painful stimulus, suggesting that scratching inhibits the transmission of itch in the spinal cord in a state-dependent manner.

Dry, Itchy Skin

  cartoon by Gene Blasen

This is a good discussion of the dry, itchy skin many people experience during winters: 
It’s Cold and Your Skin Is Suffering. So What Are You Doing to Moisturize? 

It begins:  IT’S been a challenging winter for people with dry skin. The country has been blasted with Arctic air, making this winter the coldest so far in a decade, according to Scott Stephens, a meteorologist with the National Oceanic and Atmospheric Administration National Climatic Data Center. With the cold comes low humidity — sometimes as low as 10 percent — along with moisture-stripping winds that can cause chapped, flaky skin."

This article has some practical (and very inexpensive tips) as well as an interesting multimedia presentation.

Breast Eczemas

Toronto dermatologist, Benjamin Barankin and M. Shirley Gross wrote an important article on nipple and areolar dermatitis in breast feeding women in 2004.  This is of great import.

Abstract.  Eczema of the nipple and areola can occasionally develop in the breastfeeding patient and is associated with sore, burning, and painful areolae and nipples. Management includes elimination of any precipitating allergens and irritant and the judicious use of appropriate topical corticosteroid preparations. Patients must also be offered effective pain control and support. The proper diagnosis and management of eczema of the nipple and areola in breastfeeding patients will prevent premature and iatrogenic weaning.

This is an important area for pregnant and breast feeding women.  Often, eczema is the underlying cause, compounded by secondary infection and/or contact dermatitis. It may be that the immune dysregulation of pregnancy contributes to this subset of eczema.  DJE

The pdf is here for those who need more information see:  Download Nipple and Areolar Eczema i