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A White female presented with pruritic, reticulated, erythematous plaques on the abdomen

A 27-year-old White female with a past medical history of arthritis, asthma, and iron deficient anemia presented with pruritic, reticulated, erythematous plaques on the abdomen. The lesions first appeared when the patient was a teenager. They remained erythematous for a week and then healed with postinflammatory hyperpigmentation. The rash flares several times during the year.

What is your diagnosis?

Reticular erythematous mucinosis

Prurigo pigmentosa

Erythema ab igne

Dermatitis herpetiformis


Prurigo pigmentosa (PP), also known as Nagashima’s disease and “keto rash,” is an uncommon inflammatory skin condition of unknown etiology. It is characterized by pruritic, erythematous papules, papulovesicles, and vesicles that appear in a reticular pattern, most commonly on the trunk. The lesions are typically followed by postinflammatory hyperpigmentation (PIH).

Although PP has been described in people of all races, ages, and sexes, it is predominantly observed in Japan, often in female young adults. Triggers may include a ketogenic diet, diabetes mellitus, and pregnancy. Friction and contact allergic reactions to chrome or nickel have been proposed as exogenous trigger factors. Individual cases of Sjögren’s syndrome, Helicobacter pylori infections, and adult Still syndrome have also been associated with recurrent eruptions.

The diagnosis of PP is made both clinically and by biopsy. The histological features vary according to the stage of the disease. In early-stage disease, superficial and perivascular infiltration of neutrophils are prominent. Later stages are characterized by spongiosis and necrotic keratinocytes.

The first-line therapy for prurigo pigmentosa is oral minocycline. However, for some patients, doxycycline, macrolide antibiotics, or dapsone may be indicated. Adding carbohydrates to a keto diet may be helpful. In this patient, a punch biopsy was performed, which revealed an interface dermatitis with eosinophils and neutrophils, consistent with prurigo pigmentosa. The cause of her PP remains idiopathic. She was treated with 100 mg doxycycline twice a day, which resulted in a resolution of active lesions. The patient did have postinflammatory hyperpigmentation.

This case and photo were submitted by Brooke Resh Sateesh, MD, of San Diego Family Dermatology, San Diego, California, and Mina Zulal, University Medical Center Hamburg-Eppendorf (UKE), Hamburg, Germany. Dr. Bilu Martin edited the column.

Dr. Bilu Martin is a board-certified dermatologist in private practice at Premier Dermatology, MD, in Aventura, Fla. More diagnostic cases are available at To submit a case for possible publication, send an email to


1. Beutler et al. Am J Clin Dermatol. 2015 Dec;16(6):533-43.

2. Kim et al. J Dermatol. 2012 Nov;39(11):891-7.

3. Mufti et al. JAAD Int. 2021 Apr 10;3:79-87.

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