In case anyone needs a reminder of how cool Derm is: we can usually guess a patient’s dietary restrictions if they have this rash

This is prurigo pigmentosa (or Nagashima disease), it’s usually found on the trunk or neck, mostly in young women, and more common in Japan. It’s been associated with dieting and ketosis (hence its new nickname “keto rash”), as well as diabetes and pregnancy.

Thread inspired by a tweet from @ChristineJKoMD https://twitter.com/ChristineJKoMD/status/1380573431431790593

Picture source: https://escholarship.org/uc/item/6rv324m4

For those that need a bit of help with morphology If you can appreciate, the erythematous papules are arranged in broken up lines, we call this pattern reticular (or net-like). The ddx for reticular papules/plaques is not that long which helps narrow your ddx!

There is also post-inflammatory hyperpigmentation (that brownish pigment you see) from older, resolving lesions.