A case of micro-melanoma and its dermoscopic features

Sir,

A 45-year-old woman incidentally observed an asymptomatic small black papule on her left calf. She had no past history of melanoma. Physical examination revealed a small, round, black papule on her left calf, which was approximately 2.3 mm in diameter and symmetrical in shape [Figure 1a]. Also, several small brown naevi were seen scattered on the skin, with no obvious abnormality in shape or colour. There was no peripheral lymphadenopathy. Chest radiography and doppler sonography of the liver, bile ducts, pancreas and spleen revealed no anomalies. Dermoscopy (Heine Delta 20, Germany, non-polarized, ×20) of the papule on the calf revealed dark brown homogeneous pigmentation with pseudopods and abruptness of pigment patterns at the periphery, with structure asymmetry in one axis [Figure 1b]. This pigmentation had a starburst-like pattern. Histopathology revealed atypical melanocytes in the epidermis and hair root sheath [Figure 2a]. These melanocytes contained macronuclei and were hyperchromatic and heteromorphic in nature [Figure 2b]. Immunohistochemical staining revealed that neoplastic cells were positive for Melan A, S100 and HMB 45 [Figure 2c-e]. Based on these findings, a diagnosis of melanoma in situ was made.

Close

Figure 1a:

Black papule on the left calf of maximum diameter 2.3mm

Export to PPT

Close

Figure 1b:

Dermoscopy (Heine delta 20, nonpolarized, ×20) showing dark brown homogeneous pigmentation with pseudopods (yellow arrow) and abruptness of pigment patterns (red arrow), with structure asymmetry in one axis

Export to PPT

Close

Figure 2a:

Histopathology showing atypical melanocytes located in the epidermis and hair root sheath (H and E, ×100)

Export to PPT

Close

Figure 2b:

Hyperchromatic and heteromorphic cells with a macronucleus in the epidermis (H and E, ×400)

Export to PPT

Close

Figure 2c:

Immunohistochemical staining with Melan A (×100)

Export to PPT

Close

Figure 2d:

Immunohistochemical staining with S100 (×100)

Export to PPT

Close

Figure 2e:

Immunohistochemical staining with HMB45 (×100)

Export to PPT

Pigmented lesions are very common and mainly include melanocyte naevus, blue naevus, Spitz naevus, Reed naevus, pigmented basal cell carcinoma, seborrheic keratosis and melanoma. However, pigmented lesions are sometimes difficult to identify with the unaided eye, particularly when they are small. The acronyms ‘ABCD’ (asymmetry, border, colour, diameter) and ‘ABCDE’ (include ‘evolving’) were developed for melanoma screening. However, these criteria are not found suitable for pigmented lesions that are smaller than 5 mm in diameter. Some researchers have even suggested that pigmented lesions smaller than 5 mm cannot be considered as melanoma.¹ Thus these small pigmented lesions are easily misdiagnosed in clinical practice.

Public awareness of melanoma has increased in recent decades, and patients often seek medical advice when they notice a new pigmented lesion. Therefore, more number of small melanomas have been diagnosed. In 2004, Bono et al. termed cutaneous melanomas with a maximum diameter of 3 mm as micro-melanomas.² The main subtypes of micro-melanomas are in situ (about one-third) and Clark level II. The average age of patients with micro-melanoma is nearly a decade younger than that of those with early melanoma, implying that micro-melanoma lesions are identified several years before melanomas are usually detected.² Early identification of micro-melanoma may greatly reduce patient mortality rate.

The typical lesion of micro-melanoma is a black macule with well-defined borders which may be symmetric or asymmetric.² Micro-melanoma often presents as an important diagnostic challenge to the dermatologist. Dermoscopy appears to be an important aid to the diagnosis of micro-melanoma. Meta-analyses revealed that dermoscopy increases the diagnostic sensitivity of melanoma up to 25%, in comparison with the unaided eye.³ The dermoscopic features of nodular pigmented melanoma are typified by structureless blue pigmentation, predominant peripheral vessels and areas of pink and black colour. ⁴ Chaos (i.e., asymmetry of structure or colour) can be found in almost all algorithms, comprising asymmetry, irregular blotch, bizarre pattern or an atypical network.⁵ However, chaos is not 100% specific or sensitive for melanoma. A small portion of nodular melanomas (5.8%) are not chaotic in either structure or colour. With the wide use of dermoscopy, an increasing number of patients with micro-melanoma have been identified. To the best of our knowledge, a total of 23 cases of micro-melanoma identified via dermoscopy imaging have been reported to date [Table 1], and the smallest melanoma identified with dermoscopic images was 1.5 mm in diameter.⁶ Pseudopods, radial streaming and irregular network were the mainly observed dermoscopic features (in more than a quarter of patients). The frequency of pseudopods (11/24), radial streaming (7/24), and irregular network (6/24) in micro-melanoma had no significant statistical differences (χ² = 1.27, P = 0.53). In addition, no significant difference was observed in these dermoscopic features between micro-melanomas in situ and invasive melanomas.

The presence of chaos had a higher sensitivity for the detection of melanoma, as observed in six of the seven described patients.The lesion in the present case was small and symmetrical when visualised with the unaided eye, but the time of onset and the nature of evolution were unknown. The patient also had no personal or family history of melanoma. Dermoscopy revealed that the lesion had a typical starburst pattern, dark brown homogeneous pigmentation with pseudopods and abruptness of pigment patterns at the periphery which was monochromatic and asymmetrical in one axis. The starburst pattern is mainly observed in benign diseases such as blue naevus, Spitz naevus and Reed naevus, but rare in melanoma. Considering the dark colour and incomplete symmetry of the lesion under dermoscopy, melanoma was suspected. A biopsy was performed, which confirmed the diagnosis of melanoma. The patient underwent complete surgical resection, with no recurrence over the 1-year follow-up period.

This finding emphasises that there need not be an association between the size of the pigmented lesions and the diagnosis of melanoma. Presence of asymmetry or the criteria like ABCD or ABCDE and a variety of dermoscopic algorithms can be used for melanoma screening, but they may not be suitable for all patients. Hence clinicians should be vigilant when encountering such small pigmented lesions, particularly new onset black lesions. So it is important that such suspicious lesions must be biopsied and subjected to histopathological examination.