Review Acquired digital fibrokeratoma: review of its clinical and dermoscopic features and differential diagnosis Shawn Shih 1 , BA, and Amor Khachemoune 2,3 , MD, FAAD, FACMS 1 University of Central Florida College of Medicine, Orlando, FL, USA, 2 Veterans Affairs Medical Center, Brooklyn, NY, USA, and 3 SUNY Downstate, Department of Dermatology, Brooklyn, NY, USA Correspondence Amor Khachemoune, MD, FAAD, FACMS Veterans Affairs Hospital and SUNY Downstate Dermatology Service 800 Poly Place Brooklyn NY 11209 USA E-mail: amorkh@gmail.com Conflicts of interest: None doi: 10.1111/ijd.14046 Abstract Acquired digital fibrokeratoma (ADFK) is a rare, benign, fibrous tumor that most often occurs on fingers. It may resemble a rudimentary supernumerary digit and is often misdiagnosed as another common benign condition, such as common wart. It is typically asymptomatic and occurs as a solitary nodule less than 1 cm in diameter. Oftentimes ADFK shares clinical and/or histologic resemblance with other benign and malignant cutaneous conditions so it is crucial that careful examination is undertaken. In this article, we will discuss the clinical presentation, epidemiology, etiology, dermoscopic and histologic findings, management, and differential diagnoses for ADFK, with the hope that this review will facilitate timely diagnosis and management for this distinct condition. Introduction Acquired digital fibrokeratoma (ADFK) is an uncommon, benign, acquired fibrous tumor that most often occurs on fingers. 1–3 It may resemble a rudimentary supernumerary digit and is often misdiagnosed as another common benign condition, such as common wart. 1,4 Bart et al first described 10 cases of this condi- tion in 1968 and named this growth acquired digital fibroker- atoma. 1 However, this condition can occur not only on the fingers but also on the palm, toes, and sole. 3,5–8 Therefore, it has been suggested that the name “acquired fibrokeratoma” or “acral fibro- keratoma” would be more appropriate for this condition. 1,3 Although ADFK is a rare entity, it is important to differentiate this condition from other benign and malignant lesions for proper diagnosis and management. In this review, we will discuss the clinical presentation, epidemiology, etiology, dermoscopic and histologic findings, and management for ADFK. We will then list the differential diagnoses for ADFK and describe their important characteristics in order to elucidate the differences among them. Clinical Presentation and Epidemiology ADFK is typically asymptomatic and occurs as a solitary, flesh- colored papule or nodule less than 1 cm in diameter (Fig. 1), but less commonly it may present as a symptomatic nodule much larger than 1 cm and can cause significant pain, also known as giant acquired digital fibrokeratoma. 9,10 It most com- monly occurs on the fingers but can also be seen on the palm, toes, and sole. 3,5–8 Depending on the location of origin, the lesion can also be named acquired periungual fibrokeratoma (APF, Fig. 2) and acquired subungual fibrokeratoma. A rare variant known as multibranched acquired periungual fibroker- atoma was first described in a case report by Moriue et al. in 2014. 11 The lesion had two branching, firm, flesh-colored, small, rodlike nodules that appeared fused on the proximal nail fold, and a third 2-mm small nodule was found branching off under the nail fold. 11 Two more cases of multibranched APF were described by Goktay, in which 2–5 mm thick multibranched structures were seen protruding between the cuticle and the nail plate. 12 Additionally, one case in which ADFK presented as a cluster of multiple plantar nodules has been described. 13 ADFK occurs primarily in adult males with an age range of 39–77, though cases of female adults have also been reported. 10,12 It has been reported in patients from different ethnicities and racial backgrounds, as reported in German, Polish, Japanese, French, and Indian literature. 9 Etiology The etiology is presumed to be trauma or repetitive irritation, as reported in a few cases. 1,10 It has been suggested that ADFK results from neoformation of collagen by fibroblasts, because ª 2018 The International Society of Dermatology International Journal of Dermatology 2018 1