Pigmentation in reticular pattern and in wedge shape is apparent on the upper part of the back. Red papules and tiny excoriations are visualizable amidst the netlike pigmentation, findings that are not encountered in the confluent and reticulated papillomatosis. The parts affected in this patient are sites of predilection for prurigo pigmentosa, a condition typified by the presence of both red papules and netlike pigmentation in wedge-shaped distribution on the back, as in the case here. The findings in sections of tissue from this patient were said to be those of a superficial perivascular infiltrate of lymphocytes which is not expected in the confluent and reticulated papillomatosis, a process we consider to be a variant of acanthosis nigricans and, therefore, devoid of an infiltrate of inflammatory cells. The response of lesions in this patient to azitromycin is in accordance with the experience of Yazawa et al., who bore witness to the efficiacy of macrolide antibiotics in prurigo pigmentosa.⁵⁶

In the May issue of the Hautarzt for 2002 was published a letter to the editor from Prof. Nishikawa of Tokyo. ¹¹⁰ In it he stated that the more reasonable diagnosis in the patient shown here is prurigo pigmentosa. In their written reply, the authors of the original publication, Weigl and Abeck, did not agree with the suggestions of Nishikawa and gave as reasons the absence of ketosis, the mildness of the pruritus, and the relatively slight pigmentation.¹¹¹ In our judgment, no compelling evidence has yet been offered that ketosis is relevant to pathogenesis of prurigo pigmentosa, the majority of patients with the disease having no alterations of metabolism. The degree of pruritus varies greatly in patients with prurigo pigmentosa, as does the extend of pigmentation. The degree of enhanced pigmentation, which is postinflammatory, is related to the color of the normal skin of the patient and, therefore, may be less prominent in Caucasions than in Asians. We agree with Nishikawa.