Melanonychia
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Melanonychia, also referred to as nail melanonychia, refers to brownish, brown, gray, or black discoloration of the nail plate. Most commonly, it takes the form of a longitudinal band running from the nail matrix toward its free edge. The color usually results from the presence of melanin in the plate; however, a similar appearance can be caused by blood, microorganisms, external pigments, and certain medicinal substances. Melanonychia is a symptom, not a standalone disease diagnosis. Its causes include physiological processes, trauma, infections, inflammatory diseases, the effects of medications, benign melanocytic proliferations, and melanoma of the nail apparatus. Evaluation requires taking into account the patient's age, the duration of the lesion's development, the number of affected nails, the clinical and onychoscopic picture, and the dynamics of pigmentation.
Melanonychia - where does a dark line on the nail come from
A longitudinal dark line most commonly arises in the matrix, which is the tissue responsible for producing the nail plate. Matrix melanocytes produce melanin, which is incorporated into the forming keratin and moves distally as the nail grows. This mechanism may involve melanocyte activation or an increase in their numbers.
The main groups of causes include:
- Physiological melanonychia, more common in individuals with darker skin phototypes. It usually involves several nails and forms multiple regular bands.
- Repetitive microtrauma, footwear pressure, nail biting, cuticle picking, and chronic irritation of the matrix.
- Inflammatory diseases, such as lichen planus, nail psoriasis, chronic paronychia, and certain forms of dermatitis.
- Infections, primarily onychomycosis caused by pigment-producing fungi. Certain bacteria can also cause dark discoloration.
- Medications, including certain cytostatics, antimalarials, antivirals, antibiotics, retinoids, and agents that influence melanocyte activity.
- Systemic diseases and syndromes presenting with hyperpigmentation, especially hormonal disorders, nutritional deficiencies, and genetic syndromes.
- Benign melanocytic proliferations, such as matrix lentigo or melanocytic nevus.
- Nail apparatus melanoma, which can develop in the matrix, bed, or nail folds.
A dark line can be mimicked by a subungual hematoma, pigment deposits, foreign bodies, and staining from polishes, henna, nicotine, or chemical agents. Determining the type of pigment represents the first step of diagnosis.
Melanonychia - what it looks like
Classic longitudinal melanonychia presents as a band extending along the axis of nail growth. The color can be light brown, dark brown, gray, or black. The width of the band corresponds to the part of the matrix where the pigment is produced. Melanonychia can involve a single nail, several plates, or most fingernails and toenails.
In clinical evaluation, the following are important:
- the number of involved nails;
- the width and borders of the band;
- the parallelism of the lines forming the pigmentation;
- color uniformity;
- the location of the lesion within the plate;
- the condition of the nail folds;
- the presence of cracking, thinning, or destruction of the plate;
- the rate of widening of the band.
Benign melanonychia often forms a narrow, homogeneous band with regular borders. On onychoscopy, parallel lines of similar color, thickness, and spacing may be visible. Melanocyte activation more frequently causes gray discoloration and affects multiple nails. A matrix nevus usually corresponds to a brown band occurring on a single nail, particularly in children and young adults.
A subungual hematoma can be red, purple, brown, or black. Over time, it moves toward the free edge with the growth of the plate. In contrast, melanocytic pigment originates within the matrix and maintains a longitudinal pattern.
The presentation in children requires a separate interpretation. Benign matrix nevi in this group may display a wide band, color variation, and pigmentation of the cuticles—features that raise greater suspicion in an adult. Nail apparatus melanoma in childhood is an exceptionally rare neoplasm.
Melanonychia - when to worry
A newly developed longitudinal band on a single nail of an adult requires dermatological evaluation, especially in the absence of an obvious traumatic or drug-induced cause. Melanoma of the nail apparatus is rare, but early pigmentation may resemble a benign lesion. No single feature visible to the naked eye is decisive for diagnosis.
Features increasing the suspicion of a malignant process include:
- appearance of the band in adulthood;
- involvement of a single nail;
- gradual widening of the lesion;
- greater width of the band at the proximal fold, creating a triangular pattern;
- the presence of several shades of brown, gray, and black;
- asymmetry and irregular borders;
- lines differing in thickness, spacing, color, and direction;
- darkening or increasing intensity of pigmentation;
- extension of the pigment onto the cuticle or nail folds, referred to as Hutchinson's sign;
- microscopic pigmentation of the nail fold visible on onychoscopy;
- cracking, splitting, elevation, or atrophy of the nail plate;
- bleeding, ulceration, a nodule, or chronic granulation;
- a previous melanoma or a family history of this cancer.
Urgent consultation is required for a rapidly evolving lesion, nail destruction, pigmentation of the surrounding skin, ulceration, or a nodule. Such a clinical picture should not be masked with nail polish, hybrid manicure, gel, or cosmetic pigmentation before the diagnostic process is completed. Self-performed mechanical filing or preparation of the nail plate can obscure clinical features and make it difficult to select a biopsy site.
Melanonychia - what tests are needed
Diagnostics begins with a detailed medical history. The doctor determines the onset of the lesion, its growth rate, past trauma, manicure and pedicure procedures performed, medications used, occupational exposure, chronic diseases, and family history of skin cancers. All nails, skin, and mucous membranes are assessed, as multifocal pigmentation suggests a different mechanism than a single acquired band.
Basic diagnostic methods include:
- Clinical examination of the nail apparatus, with particular assessment of the matrix, nail plate, nail bed, and folds.
- Onychoscopy, which is a dermoscopic examination of the nail under magnification. It allows the analysis of line distribution, colors, pigment granularity, and Hutchinson's and micro-Hutchinson's signs.
- Photographic documentation and digital onychoscopy, useful in selected low-risk lesions qualified by a dermatologist for monitored observation.
- Nail clipping evaluation, which can reveal melanin, blood, fungi, or another source of pigmentation.
- Mycological examination, including direct examination, culture, histochemical testing, or molecular methods when the presentation suggests an infection.
- Laboratory tests, selected based on medical history and systemic symptoms. They may involve a complete blood count, iron metabolism, vitamins, hormones, or organ function.
- Nail matrix biopsy, which is the decisive method when melanocytic proliferation is suspected.
The biopsy technique is selected by a dermatologist or a surgeon experienced in diseases of the nail apparatus. The specimen should include the site of pigment origin and allow the assessment of melanocyte architecture. In case of suspected melanoma, histopathological examination supplemented by properly selected immunohistochemistry is of key importance. A properly planned procedure increases the diagnostic value of the sample and reduces the risk of permanent nail dystrophy.
Melanonychia - what's next after diagnosis
Management depends on the mechanism of pigmentation. Stable physiological melanonychia usually requires photographic documentation and follow-up according to the dermatologist's recommendations. In post-traumatic lesions, reducing pressure and microtrauma is fundamental. A hematoma should migrate toward the free edge as the nail plate grows.
An infectious cause requires identification of the microorganism and targeted treatment. Treatment of a fungal infection may include topical or systemic medications, depending on the pathogen species, the extent of the lesions, and the patient's condition. Drug-induced melanonychia is evaluated by the attending physician, who considers the possibility of modifying the therapy. Discontinuing the medication on one's own may expose the patient to an exacerbation of the underlying disease.
A benign nevus or lentigo may be monitored or excised when the clinical presentation, location, and test results support such an approach. Confirmed melanoma of the nail apparatus requires oncological treatment. The extent of surgery depends on the location, thickness of infiltration, deep tissue involvement, and the stage of the disease. In advanced disease, systemic treatment is also used, including immunotherapy or molecularly targeted therapy, if the tumor's characteristics justify its use.
