Junktionaler Nävus

Siehe auch das separate Black and Brown Skin Lesions Artikel.

What is a junctional naevus?

A melanocytic naevus (or 'mole') is a common benign skin lesion due to a local proliferation of pigment cells (melanocytes). A brown or black melanocytic naevus contains the pigment melanin, so may also be called a pigmented naevus. A junctional naevus has groups or nests of naevus cells at the junction of the epidermis and the dermis, and presents as a flat mole.¹

Junctional naevi are often quite darkly pigmented and are macular or very thinly papular with only minimal elevation above the level of the skin² . A junctional naevus is an acquired lesion and as they age they can change their characteristics to that of a compound naevus, where there are accumulations of melanocytes in the dermis and at the dermo-epidermal junction, which cause the lesion to become increasingly papular.

Junctional naevi occur at any site on the body and are regularly shaped, usually round or oval. They are most often uniform in colour and range in pigmentation from light to dark brown. They are usually <7 mm in diameter. They are benign lesions but have the potential to undergo transformation to bösartiges Melanom.³

How common is junctional naevus? (Epidemiology)

There are no reliable figures for the prevalence of melanocytic naevi or junctional naevi in the general population but they are exceedingly common in congenital and acquired form. They appear in all age groups.⁴ Their prevalence is so high that some believe they cannot even be considered an abnormality or pathological entity, as most people with light-coloured skin will have at least a few. They are much more common in ethnic groups with light skin but they still have an appreciable prevalence in those with more pigmented skin. The true frequency of malignant transformation to melanoma is unknown but is known to be higher in lesions greater than 20 cm⁵ .

Präsentation

Junctional naevus symptoms

• Establish if the lesion is congenital or acquired (junctional naevi are usually acquired).

• Wenn eine Läsion medizinisch auftritt, ist es wichtig festzustellen, ob damit verbundene Symptome aufgetreten sind, wie zum Beispiel:
  

  • Vergrößerung.

  • Änderung in Form oder Größe.

  • Veränderung der Pigmentierung.

  • Juckreiz/Schmerzen/Reizung.

  • Blutung.

Junctional naevus signs

• Untersuchen Sie die Läsion bei hellem Licht, vorzugsweise bei Tageslicht, falls verfügbar.

• Use drawings or photography to note the site(s), size and pigmentation of the lesion(s).

• Assess for Asymmetry of the lesion, Border (any irregularity?), Colour of lesion, Diameter of the lesion.

• Establish that the lesion has the typical pattern of pigmentation and is not significantly raised from the level of the skin, to confirm as a junctional naevus.

• Distinguish from other similar pigmented macules that affect the skin:
  

  • Freckles (ephelides) are usually multiple, small and darken after sunlight exposure.

  • Café-au-lait spots are usually larger, lighter in pigmentation and have very distinct borders.

  • Lentigines are small, sharply circumscribed and pigmented, surrounded by normal-appearing skin and tend to be multiple, lighter brown and more irregular in shape.

  • Melanome neigen dazu, dunkler zu sein, einen unregelmäßigen Rand zu haben, asymmetrisch zu sein und kürzlich gewachsen zu sein.

  • Any lesion that has increased in size, become irregular in shape, changed its colour, become heterogeneous in pigmentation, become inflamed, bled, crusted or oozed suggests a possibility of melanoma and should be assessed by excision biopsy.

Differentialdiagnose⁶

• Malignes Melanom.

• Lentigines.

• Atypisches Muttermal (dysplastischer Nävus).

• Andere melanozytäre Nävi.

• Pyogenes Granulom (usually reddish but may be brown, usually elevated from skin surface).

• Seborrhoeic keratosis (usually elevated).

• Acanthoma.

• Histiocytoma.

• Skin tag (acrochordon, elevated).

• Aktinische Keratose.

• Plattenepithelkarzinom.

• Nävi von Ota und Ito.

Untersuchungen

• No investigations are necessary in the case of a simple acquired junctional naevus that has not undergone any recent change.

• Einige Dermatologen verwenden möglicherweise die Dermatoskopie, um die Art von pigmentierten Läsionen zu unterscheiden.⁷ The value of this technique has been demonstrated by several meta-analyses.⁸ A new sign - the 'mistletoe sign' - has been described for junctional naevi which are in the inflammatory phase.⁹

• More recent diagnostic techniques for the identification of melanoma include:¹⁰
  

  • In vivo confocal scanning laser microscopy (which uses laser scanning to produce digital images of a patient's skin, with cellular detail similar to that obtained from histology of surgical biopsies).

  • MelaFind® (an automated computer-vision system that captures multi-spectral digital data from pigmented skin lesions).

  • SIAscopy (a non-invasive technique for detecting micro-architectural information, using near infrared and visible spectra light shone from a handset through the skin).

  • Genomic detection.

• Bei Verdacht auf ein malignes Melanom ist die Untersuchungsmethode der Wahl die Exzisionsbiopsie.¹¹

• Perform excision biopsy or refer if there are ≥2-3 of the following features:
  

  • Size greater than 7 mm.

  • History of itching.

  • Evidence of inflammation or redness.

  • Increase in diameter.

  • Change in colour, particularly streaming of pigment at edges.

  • Irregular or asymmetrical shape.

  • Previous oozing, crusting or bleeding.

Junctional naevus treatment and management²

• If the diagnosis of junctional naevus is clear and there has been no change in a long-standing lesion then reassurance and monitoring of the lesion are all that is usually required.

• Where there is any doubt as to the diagnosis, perform excision biopsy or refer for dermatological advice. A French study emphasised the importance of training for GPs in the early detection of potentially malignant lesions.¹¹

• Führen Sie eine Exzisionsbiopsie durch, wenn die Läsion Folgendes aufweist:
  

  • Gewachsen.

  • Symptomatisch werden.

  • Entwickelte Asymmetrie.

  • Entwickelte eine unregelmäßige Grenze.

  • Hat seinen Grad oder sein Muster der Pigmentierung verändert.

  • Entwickelte Satellitenläsionen.

Komplikationen und Prognose

Junctional naevi are, on the whole, benign lesions with a very low risk of transformation to malignant melanoma. Patients with multiple lesions and high sun exposure or episodes of sunburn may be at higher risk of developing melanoma and should be warned of potentially alarming symptoms and reviewed if there is any cause for concern.