Thread by @DrStevenTChen

Let's go back to the basics today, and talk about some #morphology in the #dermatology exam.

Today's #tweetorial/#medthread will be about evaluating....

SCALE!

#MedEd #FOAMEd #dermtwitter #medtwitter #dermatologia pc:@dermnetnz
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Before we get too far into it, how do we think about #scale? Meaning, which one of the following is it?
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When we say "primary lesion," we mean the most basic element of a lesion/rash (papule, macule, patch, plaque etc).

SECONDARY CHANGE (which scale is) means the extra exam element that occurs on top of the primary lesion!

Tertiary/Quaternary isn't a thing. I'm just a jerk.
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Now let's talk about the different kinds of scale you can see.

Some of these are "key words" that trigger a certain diagnosis in a dermatologist's mind.

If you hear someone say "micaceous scale" on a salmon colored plaque, think psoriasis. See how it looks like mica?
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While we're on psoriasis, let's talk about scale in the scalp. You can get "amiantaceous scale," which is from the French "amiante," for asbestos. It can be seen in a lot of skin diseases, but I usually think psoriasis. It's so thick that the scale can slide on the hair shaft!
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Another "key word" that we use is ichthyotic scale. Remember, the word ichthyosis is from Greek: ἰχθύς, ichthys, meaning fish, so ichthyotic means "fish-like."

When we see this, it could just be a "lotion-deficiency," but when it's severe, it certainly could be genetic!
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When the skin is super super dry, we might say someone has "asteototic scale," which means their skin looks like a "dry and cracked river bed." The other name for this asteototic eczema is eczema craquele, which is a great descriptor!
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The next "key word" is "branny scale," which is meant to look like oat bran. This is what we'll say when we're trying to describe something "pityriasiform," like what is seen in pityriasis rosea.

DISCLAIMER: I still think this is the hardest to make out!
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However, patients with "waxy scale" or "waxy keratoderma" are likely to have pityriasis rubra pilaris (PRP).

See how in photo 1 - it looks "waxy."

In photo 2, it looks "branny" again, because this is also "pityriasiform."

The follicular accentuation also is typical of PRP!
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"Ostraceous scale" describes scaling that is so thick that it looks like an oyster shell. I was always taught to check an RPR when I see this type of scaling, but it can be seen a variety of diagnoses, including bad eczema, psoriasis (as is this picture), etc.
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And where the scale is in relation to the rash is also helpful! For example, if you see an annular rash with scale on the leading edge (outside/expanding side), think Tinea (pic 1). But if you see it on the trailing (inside) edge, think erythema annulare centrifugum!
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And one of my favorite findings is the "collarette" of scale. This means there's a little ring of scale, which is actually just a footprint for where a vesicle or bulla used to be. So when we see this, we know that while it's scaly now, it used to be a vesicobullous eruption!
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A reminder - that in skin of color, things can look very different! Notably, erythema is lot harder to see! Take a look at these examples:

Pic 1 - ichthyosis
Pic 2 - PRP (with follicular accentuation!)
Pic 3 - Psoriasis

Thanks to @BrwnSkinMatters for highlighting this!
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And one last point - if you see scale, you can probably further deduce two points:

1) There is some pathology/process in the epidermis and or superficial dermis.
2) Your primary lesion is most likely a plaque or papule. Macules and patches can have them too, but less likely.
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Summary!
- Scale is secondary change in addition to the primary lesion, which is probably a papule/plaque.
- There are "key words" that dermatologists use to imply the diagnosis.
- Collarettes of scale mean there was probably a vesicle/bulla there before.

Hope this helps!
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