Thread by @DrStevenTChen

Syphilis! RMSF! Hand-foot mouth!

Slow down there, Tiger! Let's dive deeper into:

ACRAL RASHES - a #tweetorial/#medthread
(aka rashes on the "palms and soles" - kind of 😉).

#MedEd #FOAMEd #medtwitter #dermtwitter #dermatology #dermatologia pc:@dermnetnz
1/

No where else on the body does a rash evoke more of a knee-jerk differential. That's not wrong per se, as we all learn this in med school, but it's more complicated then starting doxycycline and checking an RPR!

Let's start with a definition - what does "acral" actually mean?
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Technically, "acral" just means our distal body parts. So while we often think of palms and soles, it's actually inclusive of the whole hand, the whole foot, ears, and some include even the nose!

I actually didn't learn this until #derm residency, which was shocking to me.
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A quick caveat to say that nothing on the list of diagnoses on this tweetorial are going to ONLY appear on acral surfaces, but this is what my mind runs through when I see a rash predominantly on the acral areas.

So let's start with one of the biggest mimickers of all....
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SYPHILIS! Yes, it can look like anything, but there's a specific look that makes us consider the syph even higher - described as "copper pennies." Do you see how they are brownish papules that are rather flat topped?

🙏to this paper for the photo: scielo.br/scielo.php?scr…
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Remember again, syphilis can look like anything and can be more widespread! This rash is teeming with treponemes and by the time you see this, you're already dealing with the secondary stage of this infx, so you need to treat accordingly (after you confirm the dx of course).
6/

RMSF is probably the 2nd most common dx I hear. This rash usually has a more petechial look to it.

The most important thing is that the RMSF rash comes late in the illness, so if you suspect it, don't wait/expect the rash. Just start the doxy!

Pc: medlibes.com/entry/rocky-mo…
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Hand Foot Mouth Syndrome (HFMS) is 3rd up for common in the ddx. This is definitely more common for the #tweetiatricians in #pediatrics, or in the immunocompromised.

Classically, you see blisters (vesicles) on hands, feet, & in mouth (obvi😆). Supportive care is all you need.
8/

But, the ddx for HFMS can be confusing because a lot of people will mistake erythema multiforme (EM) for it.

Notice how EM though has target lesions (red rim-->white --> red center)? Also, when the mouth has erosions in EM, it's not so focally blistered, but more diffuse.
9/

A discussion of EM has to include SJS/TEN, which has "atypical" targets.

Just to make it all jumble together, we are now seeing a lot more "atypical HFMS" which can have targetoid rash. Sorry....

My 1st ever #tweetorial was on SJS/TEN! Take a look!

https://twitter.com/DrStevenTChen/status/1094344031688146951?s=20

10/

Ok, let's do a midway recap:
- Acral means: hand, feet, ears, nose
- Copper pennies--> think secondary syphilis
- Petechiae--> RMSF (but just start the doxy!)
- Blisters in a kid --> HFMS
- Target-ish lesions: EM or SJS/TEN!
- History helps to differentiate too!
11/

Let's move to some unusual ones. The next few are seen more in #oncology/#cancer patients.

Pic 1 is of hand foot syndrome (HFS), whereas pic 2 is hand foot skin reaction (HFSR). They are different, and treated differently!

Cytarabine - think HFS
TK-inhibitors - think HFSR!
12/

HFS =redness, tingling, pain - thought to be from chemo excretion into acral sites. We tx w/ ice packs to🤲&🦶during infusions (to decrease excretion of the toxic med itself and prevent it).

In darker skin types, it might cause hyperpigmentation.
pc: cureus.com/articles/11581…
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HFSR is rather hyperkeratotic growth of skin that is painful. It's less to do with chemo excretion in these areas, & so we treat with keratolytics (urea, lactic acid topically) & topical steroids. The targeted therapies seem to cause this more.

pc: academic.oup.com/annonc/article…
14/

One more for #onctwitter! In a stem cell transplant pt, it can be hard to differentiate btw acute skin GVHD & a drug eruption.

But, skin GHVD usually starts on acral surfaces and moves in toward the torso. Morbilliform drug does the opposite!

PC: bestpractice.bmj.com/topics/en-gb/9…
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One other tip to differentiate drug from GVHD - Skin GVHD tends to be more follicular! This also corresponds to the #dermpath finding that GVHD involves the acrosyringium more (meaning the interface we see goes down the follicle more in GVHD!).
PC: imagebank.hematology.org/image/28141/ac…
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And one last elusive one. Don't forget about our humble friend, Sarcoptes scabiei! That rash in the interdigital spaces makes us all put gloves on, but remember to look at the areola, armpits, umbilicus, and groin.

Here's my scabies #tweetorial:

https://twitter.com/DrStevenTChen/status/1156707598852349952?s=20

17/

Second recap!
- Onc patients can get HFS from cytotoxic chemo, HFSR from targeted therapies
- BMT patients who get GVHD have a predilection on acral surfaces first. It's also more follicular
- If the pt is itchy, think scabes!
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This is not exhaustive, but hopefully illustrative that there are more to think about than just syphilis, RMSF, & HFMS when you see an acral rash!

We didn't discuss PPKs/keratodermas since they're so rare. Next time!

Feel free to add more if you have 'em! 🙏for joining!
19/19

Thanks to @PedsID4Life & @CaitlinNLi for one more: papular and purpuric gloves & stocking syndrome (PPGSS)!

Usually parvo, but other viruses & drugs have been reported causes! Tx is supportive, & exam=sharply demarcated painful acral rash!

Pc: semanticscholar.org/paper/Parvovir…
20/20