Changing birthmark worries mother of 4-year-old

The Case

DIAGNOSIS: Small congenital pigmented melanocytic nevus

Congenital melanocytic nevi (CMN) are benign proliferations of melanocytes clinically apparent at birth or within the first postnatal weeks. Although the cause is unknown, they are thought to represent defects in melanoblast development and/or migration during embryogenesis.¹

Clinically, they usually appear as round- to oval-shaped, homogenous, brown-pigmented lesions with sharply demarcated borders and, often, hypertrichosis.¹ As the child grows, the nevi undergo changes such as increase in size, new pigment deposition within the nevus, alteration in texture, and increase in coarse dark hair.

Great variability exists in the medical literature regarding the risk of malignant transformation of different-sized CMN.¹ However, it is generally accepted that the risk correlates directly with increasing size of the lesion and is estimated to be between 0% and 4% for small CMN and between 4.5% and 10% for large CMN.

Clinical signs of melanoma in children include large or expanding size, irregular borders, presence of ulceration, rapid growth, pigment distribution changes (eg, along internal border, a common malignant sign in small CMN), and clinical symptoms such as pruritus, bleeding, and pain.¹

Congenital melanocytic nevi are usually categorized on the basis of their size according to the Kopf system.² Small CMN are 1.4 cm or smaller, medium are 1.5 cm to 19.9 cm in greatest diameter, and large or giant are 20 cm or more in greatest diameter.

DIFFERENTIAL DIAGNOSIS

Differential diagnosis includes Mongolian spots, café-au-lait spots, and smooth muscle hamartomas, a developmental anomaly resulting from hyperplasia of smooth muscle associated with hair follicles and increased epidermal pigmentation. Dermal melanocytosis, such as Nevus of Ota and Ito, can be differentiated by its unilateral and often uniform blue-green-gray Mongolian spot-like pigmentation, involving the first and second divisions of trigeminal nerve or localization to shoulder, respectively.³ Melanocytic nevi that are clinically and histologically identical to CMN but arise when a child is aged between 1 month and 2 years are designated tardive CMN or congenital nevus-like nevi.⁴

TREATMENT

In the 1970s and 1980s, there was a perceived risk of melanoma developing in association with small CMN, which prompted many physicians to prophylactically remove all CMN.

With new understanding of the relatively low risk of malignant transformation of small- to medium-sized CMN, in absence of concerning clinical features or monitoring obstacles, prophylactic removal of CMN has fallen out of favor.⁴ Small- and medium-sized CMN should be managed on a case-by-case basis, taking into account worrisome changes in appearance, psychosocial cosmetic concerns, anxiety of patients and parents, and ease of monitoring. Treatment recommendations of many investigators include baseline photographs, providing the option of specialist referral, and periodic evaluation, especially postpuberty when risk of malignant changes increases.

Surgical removal is justified if a small CMN develops suspicious changes or becomes irregular, symptomatic, or located in an anatomical position (back, buttocks, or scalp) that does not allow for regular long-term observation.¹

OUR PATIENT

The risk of malignant transformation in this small- to medium-sized CMN is low. Baseline photographs were taken, reassurance was provided to the mother, monthly home mole checks were recommended, criteria for biopsy were discussed, and a follow-up appointment was suggested in 2 years.

DR HAMMOND is pediatric chief resident, Sinai Hospital of Baltimore, Maryland. DR COHEN, the section editor for Dermatology: What's Your Dx?, is director, Pediatric Dermatology and Cutaneous Laser Center, and associate professor of pediatrics and dermatology, Johns Hopkins University School of Medicine, Baltimore. The author and section editor have nothing to disclose regarding affiliation with or financial interest in any organization that may have an interest in any part of this article. Vignettes are based on real cases that have been modified to allow the author and editor to focus on key teaching points. Images may also be edited or substituted for teaching purposes.

REFERENCES

1 .Lyon VB. Congenital melanocytic nevi. Pediatr Clin North Am. 2010;57(5): 1155-1176.

2 .Kopf AW, Bart RS, Hennessey P. Congenital nevocytic nevi and malignant melanomas. J Am Acad Dermatol. 1979;1(2):123-130.

3. Morelli JG. Cutaneous nevi. In: Kliegman RM, Behrman RE, Jenson HB, Stanton BF, eds. Nelson Textbook of Pediatrics.18th ed. Philadelphia, PA: Saunders; 2007:2674-2679.

4. Price HN, Schaffer JV. Congenital melanocytic nevi-when to worry and how to treat: facts and controversies. Clin Dermatol. 2010;28(3):293-302.