Faculty Bibliography

Localized longitudinal erythronychia describes a solitary red streak limited to a single nail unit. Localized longitudinal erythronychia can be caused by both benign and malignant entities. Most commonly, the cause is a benign process, such as an onychopapilloma. We report a case of an acquired subungual arteriovenous malformation that presented as localized longitudinal erythronychia during pregnancy. To our knowledge, this is the first report of localized longitudinal erythronychia arising from a pregnancy-associated arteriovenous malformation of the nail unit.

Herein, we describe some of the more common changes in the nail unit that can be seen in systemic diseases in children. Changes that can be seen are not limited to those discussed in the following pages. The presence of changes on multiple nails is suggestive of a systemic cause in an ill child. However, multiple nails can also be affected in primary inflammatory disorders and infections of the nail unit. When evaluating a pediatric patient with a nail disorder, it is important to perform a complete physical examination of the skin and oral mucosa, as other clues to the diagnosis of the nail problem may be found. A comprehensive family history is also important to uncover possible syndromic associations with nail disease or diseases that can manifest with nail changes.

Midline mucinosis was observed in a 14-year-old man, which was confined to the midline of the back and appeared as asymptomatic, nonindurated, hyperpigmented plaques. Skin biopsies showed prominent interstitial mucinosis with perivascular lymphocytic infiltration. A literature review of plaque-like mucinosis revealed 14 previous cases with this distinct presentation that may overlap with reticular erythematous mucinosis and connective tissue disease. Midline mucinosis has been previously reported in prepubertal children but is rare.

Nail cosmetics and adornments are widely used in today's society. However, their histologic features are not well characterized. Routine histologic examination and polarization of nail plate specimens in our academic dermatopathology practice at the Hospital of the University of Pennsylvania revealed 3 distinct histologic patterns of nail cosmetics: a hyperpigmented pattern with diffuse fine granular material, a layered pattern with a single linear band of polarizable material, and a hyperpigmented pattern with larger granules containing flecks of polarizable material. In our experience, submitting clinicians rarely indicate the patient's use of nail polish or other enhancements. Recognition of the histologic features of nail cosmetics is important to prevent confusion with dermatoses affecting the nail unit, and it will help dermatopathologists render more accurate diagnoses.

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.