Abstract

A 19-year-old healthy female presented with a 2.5-week history of a pruritic truncal eruption. Examination revealed symmetrical erythematous papules on the trunk and neck. The patient denied previous episodes and had minimal improvement with a short course of oral steroids, topical steroids, and oral antihistamines. She denied any new medications or exposures. Skin biopsy from the abdomen showed minimal epidermal spongiosis and mild perivascular and interstitial inflammation with lymphocytes and eosinophils. Neutrophils approximated the dermal-epidermal junction. The histopathologic findings prompted questions about diet. Several weeks prior to the eruption, she started a low carbohydrate carnivore diet. Clinicopathologic correlation made prurigo pigmentosa the most likely diagnosis. The patient returned to a well-balanced diet and the rash resolved with hyperpigmentation. Prurigo pigmentosa is a rare eruption most often presenting in young females with a symmetrical papulovesicular truncal eruption that resolves with reticulate hyperpigmentation. Histopathologic findings of prurigo pigmentosa may depend on the stage of the lesion. Common features include lymphoplasmacytic perivascular and interstitial inflammation with neutrophils and eosinophils in the dermis. Necrotic keratinocytes with melanophages have also been described. Many studies have been unable to identify a unifying trigger, although ketogenic diet has been described as a potential cause in many cases. The eruption may self-resolve or if needed, potential treatments include return to normal diet, topical/oral steroids, topical ketoconazole or tacrolimus, or oral tetracyclines. We present this case to highlight the importance of clinicopathologic correlation for prurigo pigmentosa. Sparse neutrophils at the dermal-epidermal junction may be a clue to early diagnosis.