Pathology: Hyperkeratosis, papillomatosis (increased compared to specimen B), mild epidermal hyperplasia and a superficial perivascular lymphocytic infiltrate consistent with confluent and reticulated papillomatosis.
NOTE: The differential diagnosis could include acanthosis nigricans. PAS stain is negative for fungal organisms.
Photomicrographs courtesy of Jonathan Ho MD MS, Department of Dermatopathology, Boston University School of Medicine
Diagnosis: confluent and reticulated papillomatosis.
This is a difficult diagnosis clinically and histologically. It's a type of "dermatological non-disease." Without the help of an experienced dermatopathologist I doubt that this diagnosis would have been arrived at.
The patient will be treated with minocycline, 100 mg bid for a month. If this is CARP the process will be resolved.