The Nail Flag Sign: Case Report in a Man with Diverticulitis and Review of Dermatology Flag Sign of the Hair, Skin, and Nails

A sign is a physical feature or microscopic change which can be observed when the patient or their tissue specimen is evaluated. An astute clinician or pathologist may be able to diagnose a patient’s condition by recognizing this unique morphologic feature or pathological change. In dermatology, the flag sign—alternating transverse bands of the skin or its adnexal structures that are analogous to the alternating colors of the stripes of a flag—has been associated with distinctive disorders of the hair, skin, or nails. The hair flag sign is characterized by alternating horizontal bands of hypopigmentation of the hair (in children with kwashiorkor type of protein-calorie malnutrition) or hyperpigmentation of the hair (in a male child who has intravenously received several cycles of high-dose methotrexate). In skin, the flag sign can be observed microscopically in actinic keratosis, and demonstrates by alternating parakeratosis and orthokeratosis of the stratum corneum—corresponding to the type of hyperkeratosis occurring above the interadnexal epidermis or the ostea of the acrosyringia and acrotrichia. The nail flag sign—noted in some individuals who have diabetes mellitus, diverticulitis, leprosy, or vitiligo—presents with alternating white and pink-red horizontal bands beginning at the proximal nail fold and extending distally to the free edge of the nail plate. A man with chronic diverticulitis and the nail flag sign is reported; he also has a history of congenital leukonychia, actinic keratoses, basal cell carcinoma and psoriasis. In addition, the features of hair, skin, and nail flag signs are reviewed. The detection of the dermatology flag sign can prompt a pathologist to consider the diagnosis of actinic keratosis. Alternating horizontal bands of hair color can indicate protein-calorie malnutrition or an effect of chemotherapy in a child. Certain autoimmune, inflammatory, or infectious conditions in individuals present with white and pink-red horizontal bands on their nails.