Thread by @DrStevenTChen

All right #medtwitter, ready to feel itchy? Get your Sarna ready and read on for a #tweetorial/#medthread on....

SCABIES!!!

#dermtwitter #dermatology #MedEd #FOAMEd pc: @dermnetnz #derm #itch #pruritus
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What exactly is scabies? Sarcoptes scabiei var. hominis is the technical name of this parasitic mite that burrows into the skin (itchy yet?😆). It is notoriously difficult to diagnose, and has humbled many a #dermatologist.

It has a very characteristic look under the scope!
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On exam, most know the classic distribution: interdigital spaces (pic1). However, other places to look include the areola, axilla, and umbilicus. In kids, the lesions tend to be all over the place (perhaps because they aren't as good at scratching them off! - pic2).
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Interestingly, scabies doesn't usually go all over the place. What body part is usually spared?
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The scalp is usually spared! All the other spots (eg the foot in the photo) can be involved.

In fact, the groin is so commonly involved that I was taught that a pruritic nodule on the glans penis or vulva is scabies until proven otherwise!
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Distribution is important, but the PRIMARY LESION IS KING/QUEEN. What that means is that the most distilled lesion of the rash is what gives this diagnosis away.

You should see papules with a burrow that ends in a black dot (pic1)! The dot often looks like a triangle (pic2).
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That burrow is where the mite is digging in. So to find it, that's where we go. Dermatologists will use a mineral oil prep to try to find the mite on a scraping.

There are 3 ways to identify a likely scabies infestation on a prep. Which one of the following isn't one of them?
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So if you identify the mite, its poop, or its eggs, you've got a positive prep. The photo is a mite I found when I was a derm resident. the oval thing in the mite is the egg, and the black stuff behind it is the poop!
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Let's do a mid-tweetorial recap:
✅Scabies is an infestation of the mite on human skin.
✅A mineral oil prep can confirm the diagnosis.
✅Distribution is helpful, but primary lesion is most important. It tends to spare the scalp.
✅Look for a burrow that ends in a black dot!
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So when should you suspect it? Since it is spread by direct skin to skin contact, patients who are itchy after living in tight quarters such as prisons, dorms, nursing homes, etc) are at higher risk. Also, if someone they live with also has an itchy rash, I start to worry.
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Importantly, just b/c someone the patient lives with doesn't have an itchy rash doesn't rule it out! Similarly, a negative mineral oil prep doesn't really rule it out either (very high specificity, poor sensitivity).

To be honest, if I'm even thinking it, I may just treat!
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Treatment is usually permethrin applied from the neck down to every nook and cranny before bed. Then in the AM, shower off, and all sheets/clothes laundered on high heat. Repeat in 1 week.

Alternatively, ivermectin PO can also be used (also repeated).
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Things that can't be washed easily can be bagged up for 1 week (such as a cloth sofa). The mites will die in 3 days without a blood meal.

Oh, and you can get a post-scabetic itch. That means even after adequate treatment, you can still be itchy!
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One quick note on "crusted scabies." This is the same mite, but just when it goes crazy! Think about it with immunosuppressed patients. They are LOADED with mites, & can have a "fruity aroma." Treatment is usually multiple rounds of both permethrin and ivermectin.
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Now that you're all scratching like crazy (as I have been while making this thread), let me reassure you. The chances of getting scabies from casual contact with a (non crusted) scabies pt is low.

Although a bit old, this article is a nice reference.
nejm.org/doi/full/10.10…
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So to recap the 2nd half:
✅Think about the Scabes with tight living quarters, or immunosuppression.
✅Treatment is permethrin or ivermectin; combined for crusted scabies.
✅Risk of transmission is low with casual, unless crusted scabies.
✅Post scabetic itch can linger!
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Thanks for joining me on this tour of one of the most cringe-inducing diagnoses in #dermatology. Next time you get an itchy patient, think #scabies, and you might prevent another case from going unnoticed.

& sorry about all the #Friends gifs! They just seemed so perfect😂
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