Dermatology

Dermal melanocytosis (previously known as Mongolian spot)

Are You Confident of the Diagnosis?

Characteristic findings on physical examination

These lesions are usually present at birth as blue-black macular lesions found overlying the lumbosacral area (Figure 1). The lesions can range in size from 5mm to 10cm or more. The pigment will not accentuate when observed with a Wood’s lamp. The lesions can also be noted within the first few weeks of life. Dermal melanocytosis can also be seen higher up on the back, or the lesions can extend onto the buttocks and even onto the upper posterior thighs. Lesions are darkest at 1 year of age and often are noted to be fading by 3 years of age.

Figure 1.

Classic example of dermal melanocytosis (Mongolian spot). Courtesy of Rhonda Schnur, MD

Expected results of diagnostic studies

Histology of a biopsy specimen will show hyperpigmented spindle shaped melanocytes distributed in a parallel fashion between collagen fibers in the deep dermis. Some of the lesions that persist into adulthood may show histology similar to that of a blue nevus, with some melanocytes extending into the subcutaneous fat and even into muscle.

Diagnosis confirmation

The differential diagnosis includes a large cafe-au-lait macule or blue nevus. In an older child, both post-inflammatory hyperpigmentation as well as a fixed drug eruption would be in the differential, but neither of these would be present at birth. Non-pigmented lesions, such as vascular malformations and deep cavernous hemangiomas, would also be in the differential, especially in very dark-skinned individuals. Lastly, linear and whorled nevoid hypermelanosis should also be considered if the pigmentation has a whorled pattern.

Who is at Risk for Developing this Disease?

Dermal melanocytosis can be seen in up to 90% of Asian, African American, and Native American infants, but can be seen in infants of any race. There is no difference in the incidence between the sexes. The overall incidence is 255/1,000 live births. Lesions usually spontaneously regress in early childhood, but one study showed 4% of almost 10,000 Japanese men age 18 to 22 had a persistent lesion.

What is the Cause of the Disease?

Etiology

Pathophysiology

Dermal melanocytosis occurs when melanocytes fail to complete their migration from the neural crest to the basal layer of the epidermis. The melanocytes end their migration in the middle to lower dermis, where based on the Tyndall effect, their brown pigment gives the skin’s surface a blue-grey color. The Tyndall effect describes the phenomenon whereby shorter-wavelength colors such as blue are reflected at a more superficial level in the skin, thus producing the clinical lesion seen.

Systemic Implications and Complications

For most lesions of dermal melanocytosis there are no known complications and no systemic implications have been reported. Very rarely, extensive and multiple lesions of dermal melanocytosis have been seen in association with lysosomal storage diseases (notably GM1 gangliosidosis type 1) and with vascular malformations in phakomatosis pigmentovascularis.

Treatment Options

Due to the benign and relatively self-limited nature of dermal melanocytosis, only a very few therapeutic clinical trials have been reported. As is the case for related lesions such as nevus of Ota and Ito, the Q-switched Alexandrite laser has been shown to be an effective modality for lightening lesions of dermal melaoncytosis.

Optimal Therapeutic Approach for this Disease

Due to the benign and relatively self-limited nature of dermal melanocytosis, realistically no treatment other than reassurance and "expectant observation" is necessary. As is the case for related lesions such as nevus of Ota and Ito, the Q-switched Alexandrite laser has been shown to be an effective modality for lightening lesions of dermal melaoncytosis.

Patient Management

If the lesion in question is clinically very characteristic, no work-up, treatment or follow-up is necessary. If the lesion has clinical features that put the diagnosis in question, then it is possible that several things may need to be done. First, if the lesion is midline over the lower spine, and the diagnosis is in question, it may be necessary to do an MRI to rule out underlying spinal dysraphism. If the lesion is not midline, or it is midline and the MRI is normal, a punch biopsy of the skin will usually confirm the diagnosis.

Unusual Clinical Scenarios to Consider in Patient Management

The only unusual clinical scenarios involving dermal melanocytosis are those cases with an atypical clinical presentation, such as a patient with either a very large lesion or multiple lesions as described in the complications section above. If large or multiple areas are seen in association with a vascular malformation, then a work-up for phakomatosis pigmentovascularis needs to be considered. In a complicated medical patient with a very large or multiple lesions of dermal melanocytosis, a work-up for the lysosomal storage diseases should be included in the patient’s overall evaluation.

What is the Evidence?

Kikuchi, I. "The biological significance of the Mongolian spot". Int J of Dermatol. vol. 28. 1989. pp. 513.

(A good historical review of dermal melanocytosis, which was previously known as Mongolian spot.)

Gilchrest, BA, Fitzpatrick, TB, Anderson, RR, Parrish, JA. "Localization of melanin pigmentation on the skin with Wood’s lamp". Br J Dermatol. vol. 96. 1977. pp. 245.

(An early review of a number of pigmentary disorders, including what has come to be known as dermal melanocytosis, using the Wood’s lamp to highlight the location of the pigmentation in each disorder.)

Kagami, S, Asahina, A, Watanabe, R, Mimura, Y, Shirai, A, Hattori, N. "Laser treatment of 26 Japanese patients with Mongolian spots". Dermatol Surg. vol. 34. 2008. pp. 1689.

(Describes the results of a relatively large case series of Japanese patients with dermal melanocytosis successfully treated with laser therapy.)

Ruiz-Maldonado, R, Tamayo, L, Laterza, AM, Brawn, G, Lopez, A. "Phakomatosis pigmentovascularis: A new syndrome? Report of four cases". Pediatr Dermatol. vol. 4. 1987. pp. 189-96.

(A small case series of a new syndrome, phakomatosis pigmentovascularis, of which dermal melanocytosis can be one of the findings. There are several different types of phakomatosis pigmentovascularis, and each exhibits varied forms of pigmentary and vascular anomalies.)

Hisano, A, Kasai, K, Fukuzumi, Y. "An analysis of 114 patients with dermal melanocytosis on the trunk and extremities". Scand L Plast Reconstr Hand Surg. vol. 33. 1999. pp. 231-6.

(A large review of patients with dermal melanocytosis, describing the anatomic locations of the pigmented lesions in this group of patients.)

Hanson, M, Lupski, JR, Hicks, J. "Association of dermal melanocytosis with lysosomal storage disease: clinical features and hypothesis regarding pathogenesis". Arch Dermatol. vol. 139. 2003. pp. 916-20.

(A report describing the association of either multiple lesions of dermal melanocytosis, or one very large lesion of dermal melanocytosis, being associated with one of the lysosomal storage diseases. If one sees a patient with this clinical presentation, it would be important that they be worked up appropriately.)
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