A Rash Diagnosis: Dermatology in ED

I came across a good review of how to approach an undifferentiated rash or skin lesion in ED over at EMdocs.net, that alluded to a brief diagnostic algorithm to help guide the dermatologically clueless through the differentiation of skin presentations. Dermatology is rarely an emergency physician's forte, and so I went on my way to find some more resources. Pictures paint more than words in dermatology in particular, so I've brought together the algorithms (from EM Practice) with a few images from Dermnet (both great resources for the emergency physician) to give a more visual guide.

I highly recomend reading the article at EM Practice (it's one of their free ones if you don't have access), as well as the piece at EMdocs, and why not surf Dermnet for some nice pictures to gross out your non-medico friends with.

Basic Differentiation

This is based on the appearance of the lesion or rash, as outlined in the algorithm below. Some diagnoses are not that common (or present) in Australia (eg Rocky Mountain Spotted Fever and Lyme disease), but most are fairly universal.

You all know the definitions of these, of course (check the table if you have any doubts), so I've thrown in a few pictures to make sure you can recognise them.


Maculopapular - a combination of macules and papules (in this case almost morbiliform...)


If you see macules or papules or both, you can further differentiate them:

Petechial and Purpuric

Petechiae - small, non-blanching, red-brown macules
Purpura - petechiae's bigger brother


If you see petechiae or purpura, you can also further differentiate them:

And the Others

Erythema. It's a big red area.


Vesicles - clear fluid-filled lesions < 5mm (> 5mm is a bulla)


Bullae - big, clear fluid-filled lesions


Pustules - like vesicles, but filled with pus.


Anyone game to name all of the conditions pictured above (without using dermnet...)?

For more information, check out the EM Practice article and the blog post, and brush up on those dermatology skills.


All of these images are hosted at Dermnetnz.org

Check out EMDocs.net for this and other good resources

EM Practice provide good up-to-date, literature-based summaries on topics relevant to ED physicians.


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