Melanonychia L60.8

Author: Prof. Dr. med. Peter Altmeyer

Last updated on: 29.10.2020

Synonym(s)

black nail; black nail discolouration; black nails; Melanonychia; Melonychia

Definition
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Polyätiological, mostly painless, localized - streaky or roundish - but also diffusely homogeneous, black or brown-black discoloration of the nail plate, the subungual tissue or the paro/perinychium (see nail below), which occurs on one or more nail organs and has a high diagnostic significance with regard to the development of a malignant melanoma. Melanonychia can be associated with or without nail dystrophy.

Classification
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Homogeneous even discolouration

Tumor formations
- Malignant melanoma of the nail matrix
Exogenous discolouration
- Potassium permanganate
- Dirt
- Tobacco discoloration

Striped discoloration

Melanonychia striata longitudinalis
Pigment-forming fungi (e.g. moulds, Trichophyton rubrum var. nigricans)

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Etiopathogenesis
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Melanocytic, microbiological, traumatic, proliferative or exogenous factors:

Melanocytic causes (Melaninonychia)
- Physiological in coloured people
- Melanocytic nevus of the nail root or nail bed
- Malignant melanoma of the nail root or nail bed
- Laugier-Hunziker syndrome.
Exogenous causes:
- Antibiotics (e.g. tetracyclines)
- Antimalarials ( Chloroquine, Cyclophosphamide)
- Anticonvulsants ( phenytoin)
- Cytostatic drugs (Hydroxyurea)
- Virustatics
- Dithranol
- Silver nitrate
- Potassium permanganate baths(intensive brown discoloration).
Metabolic diseases:
- M. Addison
- Hemosiderosis
- Vitamin B₁₂ deficiency
- Porphyria cutanea tarda.
Microbiological causes:
- Fungal colonization:
  - Trichophyton soudanense
  - Alternaria tenuissima
  - Fusarium oxysporum
  - Scytalidium dimidiatum
- Bacterial causes:
  - Pseudomonas aeruginosa
  - Proteus spp.
Other:
- haematoma (important differentiation from subungual malignant melanoma)
- Lichen planus.

Differential diagnosis
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The most important differential diagnostic decision is the differentiation between melanocytic and non-melanocytic pigmentation. In case of melanocytic pigmentation of the nail matrix there is always a continuous striped pattern. This is never observed in subungual haematoma (most common differential diagnosis). Microbially caused nail discolorations are generally accompanied by dystrophic changes in the nail matrix (see Tinea unguium).