Naevus spilus
Speckled lentiginous naevus; SLN; "speckled lentiginous naevus syndrome" (when associated with neurological / ocular features); zosteriform lentiginous naevus
Naevus spilus — also known as the speckled lentiginous naevus (SLN) — is a benign congenital or early-childhood pigmented lesion characterised by a uniform tan to light-brown café-au-lait-like background macule, ranging from a few centimetres to extensive segmental dimensions, with superimposed darker brown to black "speckles" representing junctional, compound or intradermal melanocytic naevi (and occasionally Spitz, blue or congenital melanocytic naevi). The lesion is driven by postzygotic somatic mosaic mutations of HRAS (most commonly p.G13R), making it part of the broader RASopathy spectrum that includes naevus sebaceus and Schimmelpenning syndrome. The melanoma risk is modestly increased compared with the general population (estimated 0.1–0.2% lifetime risk for typical naevus spilus) — predominantly arising from the speckled component rather than the background macule. Larger, segmental and "tardive" (rapidly developing) variants carry higher risk. Photographic surveillance and biopsy / excision of any atypical speckle is the standard approach.
Clinical features
- Background macule — uniform tan to light-brown café-au-lait-like patch, ranging from 2 cm to extensive segmental ≥10 cm.
- Speckles — superimposed darker brown to black 1–5 mm macules and / or papules — representing junctional, compound, intradermal, Spitz or blue naevi (occasionally congenital melanocytic naevi).
- Distribution — trunk and extremities most common; less often face / scalp.
- Onset — congenital or appearing in early childhood; speckles may continue to develop through puberty.
- Subtypes:
- Macular naevus spilus — speckles are flat lentiginous macules.
- Papular naevus spilus — speckles are raised papular naevi.
- Mixed.
- Zosteriform / segmental — large lesion in a Blaschko line or dermatomal distribution.
- Speckled lentiginous naevus syndrome — extensive naevus spilus + ipsilateral hyperhidrosis + neurological / ocular abnormalities (one of the phakomatosis pigmentokeratotica spectrum).
- Differential — café-au-lait macule (uniform, no speckles, NF1 marker), agminated lentigines, congenital melanocytic naevus, segmental neurofibromatosis.
Genetics
- Postzygotic somatic mosaic gain-of-function mutations of HRAS (most commonly p.G13R) confined to the affected lesion.
- Same gene mutated (with different specific mutations) in nevus sebaceus of Jadassohn (HRAS p.G12V) and Schimmelpenning syndrome.
- Both the background macule and the speckles harbour the same HRAS mutation, supporting a common mosaic origin.
- Mutations not detectable in blood / unaffected skin.
Melanoma risk
- Modestly increased compared with general population — estimated lifetime risk 0.1–0.2% for typical small naevus spilus; higher for large segmental / tardive lesions.
- Melanoma typically arises from a darker speckle (a junctional, compound or Spitz naevus component) rather than the background macule.
- Risk factors for melanoma in NS:
- Large size (>4 cm).
- Segmental / extensive distribution.
- Tardive / rapidly developing speckles.
- Atypical clinical or dermoscopic features in any individual speckle.
Management
- Surveillance — annual full-skin examination with photographic and dermoscopic documentation of the speckles.
- Excisional biopsy with full histology of any speckle that:
- Develops atypical clinical features (asymmetry, irregular border, atypical pigment, ulceration, rapid growth).
- Develops atypical dermoscopic features.
- Differs significantly from neighbouring speckles ("ugly duckling" sign).
- Causes diagnostic uncertainty.
- Photoprotection — avoid sunburn over the affected area.
- Cosmetic management of disfiguring lesions — Q-switched lasers may improve the background pigmentation but do not eliminate the speckles; surgical excision of cosmetically intrusive speckles or — in rare extreme cases — segmental excision of a small lesion with reconstruction.
- Counsel patients about the modest melanoma risk and the value of surveillance.
- If accompanied by neurological / ocular features (speckled lentiginous naevus syndrome) — multidisciplinary referral to neurology and ophthalmology.
References
- Vidaurri-de la Cruz H et al. Naevus spilus and melanoma — review. Pediatr Dermatol; 2004.
- Sarin KY et al. Activating HRAS mutation in naevus spilus. J Invest Dermatol; 2014.
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