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 https://abs.twimg.com/emoji/v2/... draggable="false" alt="🕵️‍♀️" title="Detektivin" aria-label="Emoji: Detektivin">

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">https://twitter.com/Christine...

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

For those that need a bit of help with morphology https://abs.twimg.com/emoji/v2/... draggable="false" alt="☺️" title="Lächelndes Gesicht" aria-label="Emoji: Lächelndes Gesicht"> 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.