Longitudinal melanonychia
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- Localization. Nails: hands or feet
- Erythematous lesion?
- Evolution time. Chronic: more than 2 weeks
- Skin lesion. Flat: macule or spot
- Surface texture. Normal/smooth
- Edges Well defined and regular
- Color. Due to pigment: brown, black or blue
- Distribution of lesions. Discreet/isolated injury: 1 to 5 injuries
- Associated symptoms.
- Additional information.
Brief information
- Melanonychia represents a brownish or black discoloration of the nail plate.
- Longitudinal melanonychia is the most common form of presentation, while transverse or total melanonychia occurs more rarely.
- Two mechanisms can explain the development of melanonychia:
- hypermelanosis or melanocytic activation: increased melanin production from the normal number of activated melanocytes in the nail matrix.
- includes physiological causes (race; pregnancy) or pathological causes (infection; inflammation; trauma; iatrogenesis; neoplasia; systemic cause; association with syndromes).
- melanocytic hyperplasia: increase in melanin secondary to an increase in the number of melanocytes in the nail matrix.
- includes lentigo (benign); nevus of the nail matrix (benign) or subungual melanoma (malignant).
- hypermelanosis or melanocytic activation: increased melanin production from the normal number of activated melanocytes in the nail matrix.
[!] The ABCDEF rule helps in the clinical diagnosis of malignant melanoma:
- A (age): occurs mainly between 50 and 70 years of age, being more prevalent in African-Americans and Asians.
- B (brown-black band): longitudinal brown to black band, width greater than 3 mm, irregular/faded edges.
- C (change): recent/rapid change in the width/morphology of the pigmented band or in the morphology of the nail plate.
- D (digit): involvement of a single digit (thumb > hallux > index finger).
- E (extension of pigmentation): positive Hutchinson’s sign – extension of pigmentation to the periungual region.
- F (family): personal or family history of dysplastic nevi or melanoma syndrome.
Differential diagnosis
- Subungual hematoma
- Exogenous discoloration
- Subungual hemorrhage
- Fungal melanonychia
- Longitudinal erythronychia
- Onychopapilloma
- Pigmented onychomatricoma
Treatment
- Periodic surveillance and evaluation, with dermoscopy if possible, when the risk of melanoma is low.
- Refer for biopsy in suspected cases of melanoma.
- Some authors suggest six possible indications for performing a biopsy (some coinciding with the “ABCDEF” rule):
- rapid/recent change, with the band becoming wider and/or darker;
- diffuse band boundaries, rather than well demarcated ones;
- irregular coloring of the pigmented band;
- black streaks on a single nail, especially in white individuals;
- deformity or dystrophy of the nail plate;
- broadband, >6 mm.
- Some authors suggest six possible indications for performing a biopsy (some coinciding with the “ABCDEF” rule):
- Surgical excision in cases of melanoma.