Monday, April 21, 2008

A dark patch on the skin

A thirty-something year old lady came in today for her physical. Among other things, she complained of a dark patch on the outside of her left ankle along with pain in the same spot. Dark patch and pain, no connections so far.

So I check it out. The patch is slightly irregular and brown with faint overtones of red. It looks like nothing familiar so far, not fungal, not eczema, not psoriasis. Not tender to touch nor hot in an inflamed sort of way.

The pain occurs while walking, so I ask to see her walk barefoot across the room. Bingo. We have a too many toes sign signaling flat feet, flatter left than right. No wonder her collapsing left ankle hurts. But what about the dark patch?

Does it itch? You bet, she says. Do you scratch it? Are you kidding, she counters, all the time. Ah ha, it's that hyperpigmented Iscratchtoomuchandirritatemyskin chronic skin change sort of look. I see that lots in the middle of the back in older people still limber enough to reach around to scratch.

Patches of skin near the spine itch due to a radiculopathy (now how good a word is that) meaning that a little nerve branch going to the skin called a radicular nerve gets pinched as it passes out of an arthritic spine. The skin supplied by this nerve starts to itch or burn, the patient scratches it lots, and the skin gets dark from chronic irritation. Then I look like an amazing medical intuitive when I ask if that area bothers them.

The brown discoloration of chronically scratched at skin is caused by hemosiderin. This pigment is a breakdown product of hemoglobin. As people dig at itchy spots over time, tiny blood vessels rupture and release hemoglobin into the skin. This iron-carrying molecule from blood is deposited into the space between cells and is subsequently broken down into hemosiderin, leaving a permanent discoloration to the skin. You often see this same blotchy brown residue in the lower legs of elderly persons with varicose veins who develop an itchy condition known as stasis dermatitis.

15 comments:

Ruth said...

I never knew the pathology behind those brown patches of skin. Interesting.

Mauigirl said...

Very interesting.

I have issues with my ankles due to my flat (pronated, actually) arches, which I've had all my life.

Scritch said...

can this discolouration occur when a woman epilates or waxes?
And is there any way to lighten it?

This blog had the only explanation of this aside from melanoma, so I ask, slightly paranoid.

Femail doc said...

Dear Scritch,

I imagine anything that chronically irritates the skin including waxing could leave a dark patch of hemosiderin behind. I know of no way to lighten it.

Judy

Anonymous said...

I have a patch like that on both ankles but my ankles don't hurt and they don't itch. It's really dark and I'm kind of self conscious about them. What do you think?

Femail doc said...

Dear Anon,

Any chronic irritation can cause darkening without other symptoms. Perhaps high-topped shoes or boots regularly rub this area? You don't mention your age, but if you are older, venous insufficiency can cause darkening without symptoms, especially common above the ankle bone on the inner aspect of the leg.

Judy

Anonymous said...

I have been looking for a reason for the dark patch on my thigh just above my knee. It is somewhat lacy, and resembles a bruise that just will not fade. I do not scratch it, and it does not hurt, but it is right where my laptop sits when I use it on my lap. Does this sound like a similar result?

Anonymous said...

Thanks for the info. I, too, have similar discoloration on both ankles and on the other side, and lately, small dark patches have been appearing on the sheen area. I am 27 yr old.I also am suffering from poly cystic ovaries syndrome.is this interrelated? any cures for the dark patches?

Anonymous said...

I have one of these dark patches in the middle of my back were my undergarments hook is. Low tech explanation but it makes perfect sense.

Anonymous said...

A year ago I (53 yr old female) developed a dark patch about 3 cm long on the left forearm just above my elbow. It itches and has become hairy. I notice that I lean on that spot a lot when I type at the computer. Still a bit odd though.

juliet.bashore said...

I believe this is called "Notalgia Parasthetica"

Liska said...

I also believe it's called notalgia paresthetica, and I think I have it. I also have pain in my shoulder blade along with the itch. From what I've read, this can become a chronic and bothersome condition. This blog post seems to make light of it when notalgia paresthetica can also be attributed to underlying cervical and thoracic spine and disc disease.

femail doc said...

Hi Liska and Juliet. Thanks for adding the name here. Liska, don't mean to make light of it, especially when the gnawing itch of my own patch interferes with my train of thought.
Judy

Anonymous said...

hello
I have had this condition for years. I have a large brown itchy patch on my back-near right shoulder blade and now spreading to back of my right arm. The only thing I find that eases the itch is vinegar!!!! I put it on a cotton ball and use a fingered back scratcher. My doctor told me its just dry skin. good luck

Karen Roberts said...

Thank you for explaining this condition. I have the same as others, large, dark, itchy patch on my back between spine and right shoulder blade. I believe it started from wearing bras.