This is just a letter to the editor in the Journal of the American Academy of Dermatology reporting a single case published in 2013.
The case was of a 24 year old white male with a 2 week history of itchy rash on his back, chest, and abdomen.
He was first treated with both oral and topical corticosteroids to no effect. A skin biopsy was performed and he was diagnosed with prurigo pigmentosa.
Unfortunately they do not go into potential causes of the rash in this patient (ie fasting, dieting, weight loss, etc.), but since this is a letter to the editor, it’s not subject to the same scientific rigor as regular journal articles.
This patient was then treated with an antibiotic, Azithromycin 250 mg, three times a day for 8 weeks (a pretty long course of antibiotics if you ask me). The rash actually resolved within 2 weeks with only some residual post-inflammatory hyperpigmentation.
The authors compare the similarities in the microscopic features of this rash with another rash called ‘confluent and reticulated papillomatosis’ or CARP for short, and hypothesize that they may simply fall on different points of the spectrum of the same disease.
The interesting part is that with CARP, a suspected cause is a bacteria called Dietzia papillomatosis, and is most effectively treated with antibiotics such as azithromycin (as used in this patient) and minocycline (one of the effective treatments of keto rash).
Could these authors be onto something?