Blå nevus

Synonyms: Tièche-Jadassohn naevus, Jadassohn-Tièche naevus, common blue naevus, cellular blue naevus, chromatophoroma, melanofibroma

Bakgrund

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. The blue naevus is a uniform structureless lesion, steel blue in colour.¹

A blue naevus is a small blue- or grey-coloured lesion of the skin, with an appearance similar to a mole. They derive their blue colour from their pigmentation with melanin and relatively deep position within the epidermis. One theory of blue naevus's origin is that they represent embryonic neural crest cells that have failed to migrate into the epidermis in the usual fashion:² . There are two forms

Common blue naevus

• The most common form, 2-7 mm in diameter.

• Slightly raised and smooth lesion with macular, papular or plaque-like appearance.

• Grey-blue to bluish-black in colour.

• Does not have any malignant potential.

• Usually a solitary lesion with a predilection for the head (especially the scalp), neck, sacral area and dorsum of the hands/feet.

Cellular blue naevus

• Much rarer than the common form.

• Larger lesion, often 1-3 cm in diameter.

• Raised lesions with a smooth surface.

• The same colour as the common form.

• Often solitary and found on the buttocks, sacral region and the back of the hands/feet.

• Large blue naevi on the trunk have been reported with cellular changes similar to a melanoma, although metastases have never been reported.³

Epidemiologi⁴

• Blue naevi are present from a young age but relatively unusual at birth.⁵

• They are common in Asian populations, with a prevalence of 3% of Japanese. The prevalence in white adults has been reported as 0.5-4%.

• They are around twice as common in women as they are in men.

The visual appearance of blue naevus

Blå nevus

© Dannii Brighton, CC BY-SA 3.0, via Wikimedia Commons

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Presentation

• Blue naevus usually arises during the second decade and do not change in shape or size thereafter.

• Rarely, they can be present from birth.

• If the cellular form of the lesion undergoes malignant transformation this usually manifests as a precipitate increase in size or, more rarely, as ulceration.⁶

• Blue naevus can be found as pigmented lesions at unusual sites - eg, the female genitourinary tract,^{7 8} beneath nails, spermatic cord, bronchus, lymph nodes and prostate. Blue naevi found in the oral mucosa are rare but can have tendency to malignancy.⁹

Differentialdiagnos^{10 11 12}

• Malignt melanom.

• Dermatofibrom.

• Melanocytic naevus.

• Combined naevus.

• Compound naevus.

• Neurofibroma.

• Histiocytoma.

• Tattooing effect (deliberate, or material accidentally pushed into the skin during trauma - eg, coalminer's tattoo, ink pens).

• Thrombosed plantar wart.

• Apocrine hydrocystoma.

• Kaposis sarkom.

• Congenital naevus.

• Granuloma telangiectaticum.

• Naevi av Ota och Ito.

Associerade sjukdomar

• Carney's syndrome/complex is a rare association of blue naevi with further abnormalities of the skin and other organs, inherited in an autosomal dominant fashion.

• Blue naevus causes cardiac, endocrine, cutaneous and neural myxomatous tumours, plus a variety of pigmented lesions of the skin and mucosae.¹³

Utredningar

• Ingen krävs vanligtvis.

• If the nature of a lesion is uncertain then dermoscopy may be performed by a dermatologist to distinguish it from melanomatous lesions.

• Occasionally even dermoscopy is insufficient and biopsy may be required.¹⁴

• Fluorescence in situ hybridisation (FISH) assay is sometimes needed to diagnose cellular blue naevi from blue naevus-like melanoma.¹⁵

Ledning ^{16 17}

• Typical lesions with no other features that would suggest an alternative diagnosis, particularly melanoma, can be left alone, and the patient reassured.

• However, as for any pigmented lesion, where there is doubt as to the diagnosis, it is safest to refer for dermatological advice.

• There are occasional reports of recurrence of the lesion in a satellite form after excision; such lesions must be examined by further excision biopsy, preferably with dermatological opinion, to exclude malignant transformation.

Komplikationer

• Common blue naevi do not have any complications, are benign and persist unchanged throughout life.

• Cellular blue naevi are also usually benign but may, rarely, undergo malignant transformation.

• Cellular naevi are larger and so more likely to present and undergo excision biopsy.

Prognos

• The prognosis for both types of lesion is excellent.

• In the rare cases where cellular naevi become malignant then prognosis is improved by earlier diagnosis, as for melanoma.¹⁸