Prurigo pigmentosa

Prurigo pigmentosa is a rare inflammatory skin disorder marked by recurrent itchy red bumps that heal into netlike brown pigmentation. Episodes are often associated with ketosis.

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Ketosis: Ketosis is a metabolic state in which the body produces elevated levels of ketone bodies. Many episodes occur during ketosis, though the precise link between ketones and skin inflammation remains uncertain.
Skin biopsy: A skin biopsy is the removal of a small tissue sample for microscopic examination. Microscopy can support diagnosis when the clinical pattern is uncertain.
Lichen planus: Lichen planus is an inflammatory disorder that commonly causes itchy, flat-topped, purple skin papules. Its persistent papules can itch, but their appearance and course differ from recurrent red lesions that leave netlike pigmentation.
Pathogenesis: Pathogenesis is the biological sequence of events that causes a disease to develop. The inflammatory process is recognized, but the exact pathway linking ketosis to lesions is unresolved.
Ketogenic diet: A ketogenic diet is a high-fat, very-low-carbohydrate eating pattern that promotes ketone production. Diet-induced ketosis has been reported alongside outbreaks of the disorder.
Histopathology: Histopathology is the microscopic study of diseased tissue to identify structural changes. Biopsy findings vary with lesion stage and help distinguish this rash from mimics.
Erythema ab igne: Erythema ab igne is a netlike skin discoloration caused by repeated exposure to heat. It can resemble the residual pattern, but heat exposure rather than recurrent inflammatory papules causes it.
Neutrophil: A neutrophil is an immune cell that rapidly responds to infection and tissue inflammation. Neutrophils appear in early lesions, but their role in initiating the disorder is not fully established.
Inflammation: Inflammation is the body’s response to harmful stimuli, involving immune activity and changes in affected tissues. Inflammatory cells in the skin create the red, itchy lesions.
Doxycycline: Doxycycline is a tetracycline antibiotic with antibacterial and anti-inflammatory effects. It is commonly used to reduce active inflammation in prurigo pigmentosa.