Longitudinal melanonychia - Nail and Distal Digit
Melanocytes normally reside in the nail matrix and nail bed, though they are typically inactive in individuals of Northern European descent. In the nail matrix, if melanin production by melanocytes is greater than degradation by keratinocytes, the result is a longitudinal band. This phenomenon can be caused by melanocyte activation, melanocytic hyperplasia, lentigo simplex, melanocytic nevus, atypical melanocytic proliferations, and acral lentiginous melanoma.
Pediatric nail melanoma is extremely rare, particularly in individuals with Fitzpatrick phototypes I and II, but carries significant morbidity and mortality. The fingernails are more commonly involved than toenails. Evaluation of longitudinal melanonychia is more difficult in children than adults due to lack of clinical and histopathological guidelines. According to recent cohort studies from Asia, the majority of pediatric cases undergo regression or stagnation, and no incidence of melanoma was found in biopsied cases.
L60.8 – Other nail disorders
707196007 – Longitudinal melanonychia
- Subungual melanoma / acral lentiginous melanoma – Most melanomas of the nail appear in adulthood, with a mean age of onset in the 50s-70s. Nail pigmentation is the presenting sign in two-thirds of cases, although melanoma may present with a mass lesion, invariably accompanied by nail dystrophy and nail plate ulceration. Rarely, lesions are amelanotic. Hutchinson sign, periungual pigmentation indicating the radial growth of subungual melanoma, is frequently seen. The thumb and hallux are most frequently affected.
- Longitudinal melanonychia is very common among those with darker skin colors, with up to 75% of Black individuals older than 20 years and nearly 100% of those older than 50 years showing longitudinal melanonychia. Nails of digits prone to trauma or those used for grasping (thumb, index, and middle fingers) are frequently affected.
- Congenital nevus / acquired nevus – Nevi cause approximately 12% of longitudinal melanonychia in adults and almost 50% of longitudinal melanonychia in children. Fingers are more commonly involved. Pseudo-Hutchinson sign (periungual pigmentation) is seen in one-third of cases.
- Subungual lentigo
- Benign nail tumors (onychopapilloma, onychomatricoma, subungual fibrous histiocytoma, verruca vulgaris, and subungual keratosis)
- Malignant nail tumors (squamous cell carcinoma, basal cell carcinoma)
- Chronic trauma-related injury (carpal tunnel syndrome, onychotillomania, onychophagia)
- Medication-induced longitudinal melanonychia (eg, zidovudine and hydroxyurea are both frequent causes of longitudinal pigment; minocycline, bleomycin, cyclophosphamide, and hydroxycarbamide have also been cited as causes of longitudinal melanonychia) (see drug-induced nail pigment)
- Infection (onychomycosis) – May present as diffuse or longitudinal melanonychia.
- Inflammatory skin diseases (psoriasis, lichen planus)
- Connective tissue diseases (systemic lupus erythematosus, localized scleroderma)
- Endocrine disorders (Addison disease, Cushing syndrome, Nelson syndrome, hyperthyroidism, acromegaly). Longitudinal melanonychia typically affects multiple fingernails and toenails. Individuals with Addison disease also show cutaneous and mucosal pigmentation.
- Nutritional disorders (protein energy malnutrition, vitamin D deficiency, vitamin B12 deficiency) and errors of metabolism (hyperbilirubinemia, alkaptonuria)
- Phototherapy, radiation (x-rays, electron beam therapy, occupational radiation exposure)
- Genetic syndromes including Laugier-Hunziker syndrome, Touraine syndrome, or Peutz-Jeghers syndrome
- Bacterial pigmentation, most commonly from Pseudomonas, Klebsiella, or Proteus, can have a greenish or grayish hue and is often located at the lateral edge of the nail.
- Subungual hematoma is often the result of trauma and is most commonly found on the medial aspect of the first toe.
- Exogenous nail pigmentation is most commonly caused by dirt, tobacco, potassium permanganate, and tar and typically does not cause a longitudinal streak. Most can easily be removed through physical means.