Frictional melanosis and its clinical and histopathological features

Background: A rippled type of pigmentation is observed on the arms, forearms, and bony prominences, more commonly in women with a history of chronic rubbing. The terminology (commonly referred to as frictional melanosis) and its relation with cutaneous amyloidosis has been debated. Materials and Methods: Twenty one patients with pigmented skin lesions with manifestations suggestive of frictional melanosis were included in the study. Detailed history, clinical and histopathological examination were conducted on all patients. Results: Brownish black macules without rippling were the most prevalent type of presentation. Arm was the most common site of involvement followed by forearm. Histopathology showed basal layer pigmentation, acanthotic epidermis, condensation of collagen and pigmentary incontinence in the dermis. Only six patients showed amyloid deposition on Congo red stain. Conclusion: Amyloid can be demonstrated by Congo red stain in certain cases only, called frictional amyloidosis. Other cases, in whom amyloid cannot be observed may be termed frictional melanosis.