Thread by @DrStevenTChen

Want to hear a joke?

What's bumpy & painful, & "read" all over?

A #tweetorial/#medthread on ERYTHEMA NODOSUM!

Now that I've lost a few hundred followers from that terrible opener😳, let's get started👇👇

#MedEd #FOAMEd #dermatology #dermtwitter #medtwitter pc: @dermnetnz
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Why talk about erythema nodosum (EN) in the first place? Well, most medical professional recognize it, will see it, but may need some help past that! If that's you, read on.
1st, exam: As the name implies- red nodules! It's usually on the legs, & they are often ill-defined.
2/

EN is commonly seen in young healthy pts, & women >> men. Of course, the patient's history is critical, as EN is a reactive process to something else! It's inflammation in the subQ fat (a panniculitis). The rash itself isn't dangerous, but should prompt looking for a trigger.
3/

The most common identifiable cause of EN is infection, specifically strep. I also consider meds in my history taking as possible triggers (esp: antibiotics & OCPs). Before we move onto the other causes, in what percentage of patients with EN do you think NO trigger is found?
4/

Studies differ in their estimate (likely due to the geographic limitations of each study). However, most estimate between 35-50% without a found cause!

Management of the above typical causes is as expected. For strep, treat the infection; and for meds, stop them if possible!
5/

Even if idiopathic, most cases of EN resolve after a few weeks! Supportive care to help hasten resolution include the use of rest, leg elevation, NSAIDs, and light compression to the legs. Prednisone or intralesional steroids can be used if the patient has severe symptoms!
6/

But that's not why you clicked on this tweetorial! Let's talk about the more rare associations to think about! Which of the following can present with EN-like lesions?
7/

All of them! But not everything is created equal. Some are truly EN, and some are mimickers.

For ex: in sarcoidosis, true EN, with hilar lymphadenopathy & arthritis, is termed Lofgren's. It portends a good prognosis. This is true EN!

(A brief aside) -
Lofgren vs Loeffler?
8/

Yet, in other diseases, they are merely mimicking EN. For ex, if a patient has a rare type of subcutaneous panniculitis-like T-cell lymphoma (SPTCL), it can look like EN, but it's actually lymphoma.

This is where if your hx includes other systemic symptoms, time for a bx!
9/

TB can be confusing because it could be either. A pt with TB may develop EN as a reactive hypersensitivity reaction to the infection, but they could be developing a rare tuberculid reaction called erythema induratum. This also looks like EN, but on the back of the legs!
10/

In IBD, EN is helpful because it can act as a harbinger for a flare!

There are other rare things on the ddx. Most are processes that cause a panniculitis:
Pancreatic dz, alpha-1 antitrypsin, vasculitides.

I learned this mnemonic before for some of the more common causes:
11/

Some take home pts:

- Red, tender, ill-defined nodules on the legs
- Usually reactive to something. Patient history dictates further w/u.
- Supportive care indicated until it naturally runs it's course.
- In rare cases, a bx may be necessary to r/o something more sinister.

12/

Thus ends my brief #tweetorial on EN!

NB - I specifically tried to make this shorter based on @tony_breu's study on #tweetorials and optimal length. If you have suggestions, would love to hear them. As always, #dermtwitter, feel free to add your thoughts below! Thanks!
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