Differentiating confluent and reticulated papillomatosis from acanthosis nigricans

Confluent and reticulated papillomatosis (CRP) is an uncommon dermatosis with a reticular pattern. As differentiation between CRP and benign acanthosis nigricans (AN) can be challenging because of their similar clinicopathological features, we aimed to distinguish the two diseases.

We retrospectively reviewed the clinical characteristics of 60 CRP and 30 AN patients. Histological examinations were conducted on 33 CRP and 30 AN lesions.

While CRP was concentrated on the trunk, AN mostly appeared in the axilla. In the AN group, the number of obese patients was higher, and acanthosis and papillomatosis were more evident. In both group, increases in Ki-67 and keratin 16 expression were similar. Bacterial infection was detected at a higher rate in CRP lesions than in AN lesions.AN lesions had greater pigmentation because of a high number of melanocytes than CRP lesions.

The location of skin lesions and body mass index are the main clinical factors that enable differentiation between CRP and AN. The epidermal histological changes in CRP are milder than those in AN. AN lesions also showed a greater degree of pigmentation and melanocytic proliferation.