Why is bilateral vitiligo bilateral?

December 1, 2008 12:25 AM

Why is bilateral vitiligo bilateral?

The pattern of depigmentation in vitiligo vulgaris is frequently symmetrical, but I can't seem to find any explanations as to why. I've been trying to find the answer on pubmed and in reviews, but it doesn't seem to be addressed very often.

I know the answer is likely to be "nobody knows", but I'm interested in what the current theories are.

posted by kisch mokusch to health & fitness (4 comments total)

Well the bilateral form of the disease appears to be genetic, which would explain the symmetry. There is another form of the disease, called "unilateral, asymmetrical" or "segmented," but no one really knows what causes either form of disease.

Here is a link to a dermatology textbook with an extended discussion of the disease. Should pretty much bring you up to speed with current medical knowledge. It's from 2006, so it's reasonably current.
posted by valkyryn at 7:11 AM on December 1, 2008

Er... the too short answer is that mammalian embryonic development is bilateral. If the issue is genetic, it is likely affecting (or affected by) the chemical push-pull of intercellular communication during development. We develop bilaterally, thus bilateral vitiligo.

Contact dermatitis and things that one catches environmentally localize around the point of contact. Thats why it's extremely unusual (but not impossible) to catch bilateral poison ivy.
posted by abirae at 8:20 AM on December 1, 2008

My amateur theory is that bilateral development has evolved through natural selection because it provides a template that reveals disease, deformity, or injury--hence less suitable mates. Amorphous organisms don't lend themselves well to the "hot or not" sexual sweepstakes. But what about a "disease" that does not affect survival? By any other name, that is just a "trait", like baldness or freckles. So turn your question around: Why should a mutation that does not affect survival not be bilateral, like most other human traits?
posted by weapons-grade pandemonium at 9:24 AM on December 1, 2008

Thank you for the replies. The current literature seems to suggest a strong autoimmune component to the disorder, but I find it hard to reconcile with the symmetry aspects.

I'm willing to accept that it's related to embryonic development, but I would have thought one would expect the pattern of depigmentation to correspond to a previously known/described skin or developmental pattern (dermatomes, Blaschko's lines etc.). Other patterns in different disorders affecting the skin can usually be explained somehow - sun exposure sites (lupus), mechanical stress (eczema), dermatomes (HSV) - but this one seems to be a bit more mysterious.

Interesting theory wgp, but freckles and moles are not strikingly symmetrical (hair is, but it's frequently the hair follicle melanocyes that are spared in vitiligo). Still, food for thought.
posted by kisch mokusch at 8:54 PM on December 1, 2008