I'm no pharmacologist, so this is written from a #dermatologist's POV!
Let's start with a question that still haunts med students today:
What is the mechanism of action of methotrexate (MTX)?
2/ MTX inhibits dihydrofolate reductase in the folate pathway, which is needed for DNA/RNA ➡️ inability for cells to rapidly divide!
Given similarities in mechanism with other drugs in this pathway, caution should be used when adding MTX on top of them, especially TMP-SMX!
Since MTX is an antifolate, remember that Folinic Acid (Leucovorin) is used as a "rescue" when side effects go crazy. But at the doses we use in #dermatology, I've never needed it. Plus, we give folate with MTX to prevent these effects!
This is a drug reaction that we can see on inpatients, with an exam full of pustules!
Let's start with a question - How long after drug exposure does AGEP appear?
2/ The correct answer is 24-48 hours!
The other answers are typical time frames for other types of reactions.
Urticaria usually manifests minutes to hours after drug exposure.
Morbilliform drug eruptions occur 4-14 days after drug exposure.
DRESS occurs 2-6 weeks afterward!
Unlike DRESS and morbilliform eruptions, AGEP doesn't require repeated exposure of drug. So one single dose can definitely cause AGEP. A typical place we see this is with perioperative antibiotics!
Common culprits are Penicillins, quinolones, sulfa, antifungals, and CCBs!
2/ First, a word of caution – this is one person’s thoughts on a new skin finding reported in a new disease that the medical community is still learning about! As such, nothing in the #tweetorial should be regarded as definite. Just wanted to share a thought process!
So, who cares? #COVID19 is devastating, at times even for the young & healthy! But it’s all respiratory, right?
Well, as we're learning, there's so much more to #SARScov2, and as a #dermatologist, this is the perfect example of how the exam helps frame possible mechanisms.
2/ First things first - some definitions:
Vesicle: fluid filled <1 cm
Bulla: fluid filled >1 cm
Pustule - Filled with pus
- Ahem, the word you're looking for describe something with a lot of pus is "purulent," not what you're thinking....🤨
3/ Next, the name is self explanatory. The vesicobullous pattern implies you're seeing vesicles or bullae. There is one very important exception:
If you see COLLARETTES of scale (round pattern of scale remnant), these can indicate a prior vesicle or bulla (like an old footprint)
2/ Psoriasis is the perfect example of a papulosquamous disorder. Before we break down what this means, let's start with the basics. I was taught that skin rashes & lesions fall in one of 5 reaction patterns:
- red (vascular)
3/ By knowing which category each rash/lesion is, you can limit your Ddx.
If something is both vesicobullous and eczematous, you're probably dealing with some type of eczema.
If you're dealing with something dermal, you can probably take psoriasis off your ddx!
2/ Let's start with appropriateness of consult. We are trying hard to limit nonurgent consults for the above reasons. The following can wait for when #coronavirus isn't everywhere.
- nonmelanoma skin CA
- old rashes with a known dx
- missed a derm appt and happens to be in house
3/ If it's an urgent issue, it's helpful to start with the photo. Any camera phone should be fine. If on Epic, you can use Haiku to upload directly the the EMR.
NB: texting photos isn't HIPAA compliant. We'll usually refer to the EMR, or email the photos in a secure system.
A patient with active bullous #pemphigoid comes to see you. What do you expect on your exam?
2/ #bullouspemphigoid (BP) is an autoimmune blistering disorder where the pt's immune system makes auto-antibodies targeting BPAg 1&2 (BP230/BP180). Since these Ags are in the hemidesmosome, the split is lower in the skin, making for tense blisters.
So what say you? What’s the reason for the Xmas Tree pattern?
2/ PR presents in "Langer's Lines," aka the skin tension lines. This paper notes diseases in this pattern seem to have activated leukocytes in the pathophy, which could be explained by other papers looking at how skin stretch impacts immune response!
Ever get all the different #dermatologic terms jumbled up? Was it erythema nodosum, erythema migrans, or erythema multiforme?
Honest poll – Ever write “rash” b/c you couldn’t remember the diagnosis?
2/ All kidding aside, these terms can get confusing. Remember though, derm terms are usually just descriptors of what you see. The name tells you all you need to know.
For example: Acute Generalized Exanthematous Pustulosis (AGEP) = pustules suddenly appeared everywhere!
3/ So, the “erythemas.” First off, what does “erythema” actually mean? Well, according to my Google machine, it's from the Greek root “eruthros” meaning “red.” So "erythema" doesn’t add much to our knowledge of what the rash looks like other than it’s red, and so, likely inflamed
Let's warm up with a question for all y'all tweeps out there!
What is the most common trigger for erythema multiforme (EM) in adults?
2/ EM is an immunologic syndrome usually triggered by infection in adults. We usually consider HSV and mycoplasma. A simple history for cold sores or genital ulcers can be telling, but mycoplasma can go undetected symptomatically.
What primary lesions do you expect in EM?
3/ EM is usually made up of papular (raised) targets. Pic1 is of EM; you can see the 3 zones in a typical target (red rim, then white, then red center). Versus SJS/TEN (pic2), where macular targetoid (2 zones of red rim, dusky center & flat).
Let's start with a question - What percentage of leg ulcers do you think is caused by venous stasis?
2/ Roughly half (40-50%) of all leg ulcers are the result of venous stasis! Since 1% of the population will get stasis ulcers at some point, it's quite common, both in the inpatient & outpatient settings!
While some say they aren't painful, many of my patients would disagree....
3/ Let's talk exam. These ulcers are predominantly on the lower legs, and often near the medial malleolus. They're usually chronic, so they may have a base covered by yellow fibrinous debris. They tend to be shallow, and given the pathophysiology, quite exudative.
How do you differentiate acute & chronic skin #GVHD?
2/ Acute vs. chronic GVHD is usually differentiated by when it occurs: before or after 100 days since allogeneic stem cell transplant. BUT in the skin, MORPHOLOGY is key!
As with almost everything else in derm, start with the exam. That will tell you what you're dealing with!
Acute GVHD is usually morbilliform, which means "measles-like." Morphologically, we describe this eruption as "3-4 mm pink papules that coalesce into plaques." Whenever we see this in a SCT pt, the ddx includes the following:
- acute GVHD
- morbilliform drug
- viral exanthem
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?
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. 3/