Update: nail unit dermatopathology.

Nail unit dermatopathology is a growing field filled with many challenges. Many advances in this field have been made in the last 5 years. This review article provides an update on new information and studies published in that period of time. We divided these works into different sections, including clinical and pathologic challenges in diagnosis and treatment of nail disorders, nail unit biopsy and processing techniques, normal nail unit histology, nail plate structural and growth pathology, metabolic disease, inflammatory conditions, onychomycosis, benign growths, malignant growths, and dyschromias. Specific highlights include advances in the marking and orientation of nail unit biopsies for improved histologic interpretation, improved nail plate softening techniques, new methods for histologic evaluation of onychomycosis, descriptions of newly described benign growths unique to the nail unit, and the morphologic and immunohistochemical distinction between benign and malignant pigmented lesions of the nail unit.