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Skin melanocytic tumor

Nevi

Nevus spilus

Authors: Syeda Qasim, M.D., Sarah E. Gradecki, M.D.

Resident / Fellow Advisory Board: Caroline I.M. Underwood, M.D.

Last author update: 28 March 2023

Last staff update: 28 March 2023

Copyright: 2021-2024, PathologyOutlines.com, Inc.

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Cite this page: Qasim S, Gradecki SE. Nevus spilus. PathologyOutlines.com website. https://www.pathologyoutlines.com/topic/skintumormelanocyticnevusspilus.html. Accessed November 27th, 2024.

Definition / general

Nevus spilus (NS) or speckled lentiginous nevus is a melanocytic lesion composed of small, dark macules or a combination of macules and papules within a larger but more lightly pigmented patch
First described by Burkley in 1842 as evenly pigmented patches, Ito and Hamado in 1952 were the first to use the term NS in speckled lesions

Essential features

Pigmented skin lesion, congenital or acquired, consisting of a large light tan patch with numerous superimposed small, dark brown macules or papules (J Cutan Med Surg 2010;14:85)
Can be seen anywhere on the body surface but the most common location is on the chest and upper limbs (Cutis 2007;80:465)
Not considered a precursor of melanoma but cases have been described in which melanoma arose in NS (Hautarzt 1996;47:759)

Terminology

Speckled lentiginous nevus (SLN)
Nevus on nevus
Naevus sur naevus
Speckled nevus spilus
Spotty nevus
Zostriform speckled lentiginous nevus

ICD coding

ICD-10: I78.1 - nevus, nonneoplastic

Epidemiology

Has no predilection for either sex but is slightly more common in individuals of Northern European descent (J Am Acad Dermatol 1995;32:957)
Most lesions are present at birth but they also may be noticed during infancy, childhood or adulthood
Prevalence varies from between 0.2% to 2.3% according to age groups and the prevalence is similar to the overall occurrence of a congenital nevus (Pediatr Dermatol 1992;9:345)

Sites

Can be seen anywhere on the body surface but the most common location is on the chest and upper limbs; lesions tend to follow lines of Blaschko (Arch Dermatol 1985;121:766)
Varies in size from 1 to 20 cm in diameter and may appear on any area of the face, trunk or extremities without relation to sun exposure (Dermatology 1994;189:382)

Pathophysiology

Unknown pathogenesis; some theories suggest a localized defect in neural crest melanoblasts (Arch Dermatol 2001;137:172)
Familial cases have not been reported but genetic factors may play a role
Mosaicism has been suggested to explain the zosteriform variant
Happle has suggested dividing NS into 2 entities, a macular type and a papular type
- Dark speckles in the macular type are more evenly distributed and represent junctional lentiginous nevi (malignant melanoma has been reported more frequently in this type) (Dermatology 2006;212:53, Dermatology 1998;197:377)

Etiology

Unknown

Clinical features

Presents as a solitary, nonhairy, flat, brown patch dotted by smaller dark brown to black macules or papules (Cutis 2007;80:465)
Earliest findings are similar to a café au lait patch, with eventual development of the secondary superimposed darker melanocytic lesions (Arch Dermatol 2001;137:215)
Can be associated with a number of other conditions, including corneal dystrophy, scleral pigmentation, hearing loss, Ebstein anomaly, neurofibromatosis type 1, epidermal nevi and nevus sebaceus
Is a component of certain presentations of phakomatosis pigmentovascularis (J Am Acad Dermatol 2021 Feb 11 [Epub ahead of print])
Speckled lentiginous nevus syndrome is the rarely occurring association of NS (usually nevus spilus papulosis) and neuromuscular abnormalities, including a sensory or motor neuropathy and hyperhidrosis

Diagnosis

Clinical presentation of NS, with a tan macule and speckled hyperpigmentation, is distinctive (Arch Dermatol 1970;102:433)
Rare cases may require a biopsy but it is critical to convey the clinical impression of NS by description or by an attached photograph, so that the pathologist or dermatopathologist can appreciate the asymmetric and sometimes subtle histologic findings (Indian Pediatr 2005;42:831)

Prognostic factors

Darker, smaller pigmented melanocytic components of NS have the potential to develop malignant melanoma, although the frequency of this transformation appears to be low
Melanoma may rarely occur in NS with an increasing incidence
- Some studies suggest a first hit postzygotic mutation predisposing to melanoma in some cases (J Eur Acad Dermatol Venereol 2012;26:129)
Risk of developing melanoma in NS is increased if NS is congenital, > 4 cm in diameter or giant or zosteriform in morphology

Case reports

4 year old boy with a light brown colored elliptical patch on left cheek adjoining the angle of lip (Indian Pediatr 2005;42:831)
33 year old woman with a medium sized nevus spilus located on the neck, successfully treated with 4 sessions of pulsed dye laser (Dermatol Ther 2017;30:e12497)
65 year old woman presenting with a nodular achromic melanoma that occurred within a nevus spilus on the left thigh (J Cutan Med Surg 2010;14:85)

Treatment

Patients should be followed regularly with clinical examination or photograph and with biopsy or excision of changing or clinically atypical areas
Cosmetically, laser treatment of nevus spilus has not been promising (Pediatr Dermatol 1998;15:407)

Clinical images

Contributed by Sarah E. Gradecki, M.D.

Light tan patch

Gross description

Light tan patch of variable size with numerous superimposed small, dark brown, well circumscribed macules or papules

Microscopic (histologic) description

Flat, tan background may show only basilar hyperpigmentation, such as is present in café au lait spots, or lentiginous proliferation of the epidermis with bulbous rete ridges
Greater degree of pigmentation is linked to an increase in the number of melanocytes in the basal layer, as well as an increase in melanin content of the basal keratinocytes
Darker macules and papules seen clinically usually contain melanocytes, which can take the form of various types of nevi including junctional, compound, intradermal, dysplastic / atypical, blue or Spitz nevi (Cutis 2007;80:465)

Microscopic (histologic) images

Contributed by Sarah E. Gradecki, M.D.

Normal melanocytes

Junctional melanocytic nevus

Basilar hyperpigmentation

Positive stains

S100
SOX10
MelanA
References: Hautarzt 1995;46:349, Am J Dermatopathol 1997;19:308

Molecular / cytogenetics description

NS is postulated to result from a postzygotic genetic alteration of the melanocytic lineage, giving rise to a clone of melanocytes predisposed to developing a neoplasm; an activating clonal point mutation in HRAS has been identified in agminated Spitz nevi arising in a nevus spilus (JAMA Dermatol 2013;149:1077)
The same HRAS mutation has been identified in 8 additional sporadic NS, suggesting that the HRAS mutation is the predominant causative mutation for NS; this mutation is sufficient to cause activation of the MAPK pathway (J Invest Dermatol 2014;134:1766)

Sample pathology report

Skin, left chest wall, excision:
- Lentiginous junctional melanocytic nevus (see comment)
- Comment: Sections show alternating areas of lentiginous junctional melanocytic nevus and areas more consistent with lentigo. In the correct clinical context, the findings could be compatible with a diagnosis of nevus spilus.

Differential diagnosis

Melanoma:
- Histological features including asymmetry, ulceration, cytological atypia, pagetoid involvement of the epidermis, lack of maturation and dermal mitoses including deep and atypical forms
Congenital nevus:
- May be junctional, compound or dermal
- Extension of nevus cells around nerves, vessels and adnexal structures is characteristic
Blue nevus:
- Bipolar spindled dendritic melanocytes associated with variable amounts of dense collagenous stroma
Spitz nevus:
- Well circumscribed and symmetrical with an overall wedge shaped silhouette
- Consists of large junctional and dermal melanocytic nests formed by spindled or epithelioid cells

Additional references

Arch Dermatol 2001;137:1655

Board review style question #1

Which of the following is a feature of nevus spilus?

Absence of rete ridges
Absence of significant pleomorphism of melanocytes
Intradermal melanocytic proliferation
Lack of basilar hyperpigmentation

Board review style answer #1

B. Absence of significant pleomorphism of melanocytes. Nevus spilus can be associated with moderate acanthosis, elongation of rete ridges and lentiginous proliferation of basal melanocytes at the dermoepidermal junction with hyperpigmentation of basal keratinocytes but not significant pleomorphism unless in rare cases the lesion progresses to melanoma.

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Board review style question #2

Which of the following is known to be associated with nevus spilus?

Arnold-Chiari malformation
Carcinomatosis
Down syndrome
Neurofibromatosis type 2
Phakomatosis pigmentovascularis

Board review style answer #2

E. Phakomatosis pigmentovascularis. Nevus spilus can be associated with other conditions including phakomatosis pigmentovascularis, corneal dystrophy, scleral pigmentation, hearing loss, Ebstein anomaly, neurofibromatosis type 1, epidermal nevi and nevus sebaceus.

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