皮膚科 劉權毅醫師

http://www.dermquest.com/expert_opinions/clinical_updates/facial_dermal_melanocytosis_common_misdiagnoses_.html
Dermal melanocytoses are usually localized and are especially common in Asians. Clinically, they all share a bluish-gray coloration. When a sufficient number of melanin-containing cells are present in the dermis, various clinical forms develop depending on their onset and distribution. Although most dermal melanocytoses are congenital or have an onset in early childhood, there is a group that is clearly acquired, with an onset in adult life. Mongolian spots typically disappear in childhood, whereas other dermal melanocytoses persist for life.

This article discusses some common facial dermal melanocytoses along with several differential diagnoses.

Nevus of Ota

In 1939, Professor Masao Ota characterized cases of aberrant mongolian spots located on the face and involving the eye, and descriptively named the disorder naevus fusco-caeruleus ophthalmomaxillaris.¹ Since then, this pigmentary disorder, which is common in Asians but rare in Caucasians, has been widely known as nevus of Ota (Figure 1).

Figure 1. A patient with typical nevus of Ota. (Image courtesy of author.)

Nevus of Ota-related dermal melanocytoses

Nevus of Ota: symmetrical type

In 1965, Hidano classified the bilateral type of nevus of Ota into two types: symmetrical and asymmetrical.² Characteristic features of the symmetrical type were summarized as:

• Symmetrical distribution;
• Mild and brown-dominant small spots scattered on lateral sites of the forehead, upper
and lower eyelids, and the malar area (Figure 2);
• No mucosal pigmentation;
• Rare and slight ocular pigmentation;
• Late onset (at age 10-30 years);
• A marked female preponderance; and
• A family history.

Hidano noted that this type of nevus of Ota appeared later than 20 years of age in one-third of patients and was frequently misdiagnosed as ephelides. As a result, he proposed it as a new clinical entity with slight differences from classic nevus of Ota.

Figure 2. A patient with symmetrical type of bilateral nevus of Ota, named by Hidano. This speckled pigmentation on the cheeks appeared in puberty and was misdiagnosed as ephelides. (Image courtesy of author.)

Acquired bilateral nevus of Ota-like macules (Hori's nevus)

In 1984, Hori et al reported 22 cases of blue-brown macules of the face, occurring on both sides of the forehead, temple, eyelids, malar area, alae of the nose, and root of the nose in middle-aged Japanese women.³ The age of onset ranged from 19-69 years. Pigmented macules consisted of blue-brown and/or slate-gray small patches (Figure 3). No patient had ocular or mucosal pigmentation. However, the same symptoms had already been described as symmetrical nevus of Ota in the Japanese literature in 1982,⁴ when one-quarter of cases had been misdiagnosed as Riehl's melanoses.

Figure 3. Patient with acquired, bilateral nevus of Ota-like macules. This discoloration, especially brown pigmentation on the temples, is frequently misdiagnosed as melasma, but is different owing to periorbital involvement and the brownish to purple tint, which can be observed on the infra-orbital area in this patient (infra-orbital ring-shaped melanosis). (Image courtesy of author.)

Nevus fusco-caeruleus zygomaticus (Sun's nevus)

In 1987, Sun et al reported a nevus presenting as a bilateral speckled discoloration of the skin of the face, principally in the zygomatic region.⁵ The condition does not normally become apparent until the second decade of life, and is much more common in women. There was also a positive family history in 18% of the cases, with a much higher incidence being seen in the general population in Taiwan. This nevus is similar to the symmetrical subtype of nevus of Ota proposed by Hidano in terms of its clinical manifestations and family history.

Infra-orbital ring-shaped melanosis

So-called "dark rings under the eyes" - an expression used by many people in everyday life - indicate pigment macules that are prominent under the eyes and appear as a condition of general fatigue, especially following periods of insufficient sleep. Similar fluctuations in color tone are frequently seen in patients with nevus of Ota.¹ Therefore, we performed a skin biopsy of the pigmented macule on the infra-orbital area taken from 12 patients who complained of dark rings under their eyes. All 12 patients displayed dermal melanocytosis and could be successfully treated with Q-swithced ruby laser (QSRL) in the same way as conventional nevus of Ota.⁶ We would like to propose, therefore, the term "infra-orbital ring-shaped melanosis" to describe the dark rings under the eyes caused by dermal melanocytosis. Furthermore, we would like to propose the term "periorbital ring-shaped melanosis" for homogenous pigment macules on bilateral periorbital areas caused by dermal melanocytosis (Figure 4).

Figure 4. Patient with periorbital ring-shape melanosis. Dermal melanocytosis is confirmed by histologic examination. (Image courtesy of author.)

Differential diagnoses

Ephelides

Ephelides are commonly dispersed over the face. Their appearance varies seasonally, being darker and more confluent in the summer but fainter in the winter. In contrast, the symmetrical type of nevus of Ota or Sun's nevus appears mainly on the zygomatic area without seasonal changes.

Melasma

Melasma is classified into epidermal, dermal, and mixed types by Wood's lamp examination. Recent histopathologic examinations, however, have questioned the existence of dermal type melasma. Most cases of dermal type melasma are considered to be Hori's nevus, Riel's melanoses or incontinentia pigmenti histologica, which all show a good response to Q-switched laser treatment. Indeed, a case of Hori's nevus and one of widespread vitiligo were presented as melasma in commercial leaflets published by several laser companies.

Melasma appears only on sun-exposed areas, eg as post-inflammatory pigmentation after sun exposure. In melasma, therefore, the periorbital area is never affected; involvement of the alae of the nose and root of the nose alone is also very rare, although distribution of the pigment is mostly symmetrical and similar to that of Hori's nevus. Melasma is usually well demarcated and uniform in color, but is rarely mottled. In Hori's nevus, however, the border is less clear, the color contains a blue or purple-brown tint, and the pigmentation is sometimes speckled. Melasma is exacerbated by sun exposure and lightened by long-term sun protection, whereas Hori's nevus is rarely influenced by sun exposure.

The treatment required for each condition is markedly different: Q-switched lasers are the only choice for the treatment of adult onset dermal melanocytosis,⁷ whereas topical hydroquinone is one of the best choices for the treatment of melasma.

Discussion

A recent prospective analysis revealed that Hori's nevus becomes progressively more confluent and grey over time.⁸ This suggests that Sun's nevus may evolve into Hori's nevus, as both nevi are almost identical.

Regarding the age of onset, there is overlap between classical nevus of Ota and both Hori's and Sun's nevi. The distribution of pigmentation is identical in nevus of Ota and Hori's nevi, although it is mostly unilateral in nevus of Ota. The histology of Hori's and Sun's nevi is identical to that of nevus of Ota. Late-onset dermal melanocytosis can be treated with Q-switched lasers, as is the case with nevus of Ota. Therefore, Hori's nevus, Sun's nevus and the symmetrical type of nevus of Ota are included under the same disorder "umbrella", which we would like to term "facial dermal melanocytosis" (Table 1).

Table 1. Facial dermal melanocytosis.

In summary, adult-onset facial dermal melanocytosis is frequently and persistently confused with other common acquired melanoses, such as melasma, ephelides and solar lentigines. Therefore, Hori's or Sun's nevi, which are pigmentations treated by Q-switched lasers, constitute differential diagnoses from the other acquired melanoses.

References

1. Hidano A, Kajima H, Ikeda S, et al. Natural history of nevus of Ota. Arch Dermatol 1967:95;187-195.
2. Hidano A, Kajima H. Bilateral nevus of Ota [in Japanese]. Jap J Clin Dermatol 1965:7;72-81.
3. Hori Y, Kawashima M, Oohara K, et al. Acquired, bilateral nevus of Ota-like macules. J Am Acad Dermatol 1984:10;961-964.
4. Harada S, Niizuma T. Symmetrical nevus of Ota [Japanese]. Practical Dermatology 1982:4;727-730.
5. Sun C-C, Lü Y-C, Lee EF, Nakagawa H. Naevus fusco-caeruleus zygomaticus. Br J Dermatol 1987:117;545-553.
6. Watanabe S, Nakai K, Ohnishi T. Condition known as ‘dark rings under the eyes' in the Japanese population is a kind of dermal melanocytosis which can be successfully treated by Q-switched ruby laser. Dermatol Surg 2006:32;785-789.
7. Watanabe S. Basics of laser application to dermatology. Arch Dermatol Res 2008:300 (Suppl 1);S21-S30.
8. Ee HL, Wong HC, Goh CL, et al. Characteristics of Hori naevus: a prospective analysis. Br J Dermatol 2006:154;50-53.

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