Characteristic Dermoscopic Features of Primary Cutaneous Amyloidosis

A Study of 35 Cases

Y.Y. Chuang; D.D. Lee; C.S. Lin; Y.J. Chang; M. Tanaka; Y.T. Chang; H.N. Liu

Disclosures

The British Journal of Dermatology. 2012;167(3):548-554. 

In This Article

Discussion

Most clinical lesions of PCA showed brownish colour and dermoscopy has been demonstrated to be an ideal tool to show the magnified characteristics of pigmented skin disorders. The dermoscopic patterns of PCA observed in this study were distinct and have never been reported before. The most characteristic dermoscopic finding of PCA, especially in MA, was a central hub, which could be either white or brown, surrounded by various configurations of pigmentation, including fine radiating streaks, leaf-like projections and bulbous projections. Nevertheless, an exact microscopic explanation for the different arrangements of pigmentation surrounding the central hubs is not clear at present. Future studies using confocal laser scanning microscopy may provide insight into the formation of the radial extension of pigmentation. This 'central hub' pattern could be found in both MA and LA, while the other pattern, 'scar-like', was present only in LA lesions. Two subtypes of 'scar-like' pattern were observed, including one resembling a volcanic crater and the other displaying completely structureless morphology. Sixteen patients demonstrated more than one above-mentioned pattern or configuration for different lesions. Therefore, we suggest that while performing dermoscopic examination for the diagnosis of PCA, a larger area or more than one affected site should be assessed in order to obtain more information.

The diagnosis of PCA is usually straightforward, especially if the morphology and distribution of lesions are typical.[1,7] However, if the area of involvement is located over an unusual site, it becomes difficult to make an accurate diagnosis. For instance, one of our patients presented with multiple pinhead-sized pigmented dots on his frontal scalp. As the scalp is seldom affected by PCA, skin biopsy was performed and MA was then proved. His dermoscopic examination showed characteristic central hubs with radial streaks. This dermoscopic picture is strikingly similar to the 'spoke wheel' pattern, which is one of the six dermoscopic criteria to diagnose basal cell carcinoma (BCC).[15] However, the distribution and homogeneity of pigmentation in PCA were different from those of pigmented BCC. In PCA, the pigment change is thought to be due to basal hyperpigmentation, melanophages in the upper dermis and amyloid deposits. All the pathological changes are located at nearly the same level of the epidermis and papillary dermis, and thus contribute to the homogeneous pigmentation. In contrast, in pigmented BCC, melanin granules are deposited haphazardly at different levels within or between tumour islands, which results in pigmentation with different colours and irregular distribution.[16,17] Furthermore, BCC displays prominent vascular components such as arborizing or truncated vessels,[18] findings not present in any of our cases.

We herein recommend that dermoscopy should be performed first for patients with atypical presentations of PCA, perhaps avoiding the need for an invasive skin biopsy. In addition, with the help of dermoscopy, PCA could be easily differentiated from other disorders such as friction melanosis and lichen simplex chronicus, the former showing brownish macules and the latter lichenified plaques with hyperpigmentation, which might clinically resemble MA and LA, respectively. As shown in Figures 4 and 5, the cases of friction melanosis and lichen simplex chronicus did not show any dermoscopic features of PCA, including central hubs and scar-like composition, providing more evidence about the specificity of these two characteristic patterns.

Previous studies have shown that the size of PCA is associated more closely with hyperkeratosis and acanthosis rather than the amount of amyloid deposition.[13] In our study, the thickness of the horny layer overlying the amyloid also affected the dermoscopic findings. In mild cases of MA, as in patient 1 in Figure 1, the horny layer showed basket-weave orthokeratosis without hyperkeratosis and, therefore, dermoscopy was able to reflect the hyperpigmentation in the basal layer and dermal papillae and, probably that was the reason why the colour of their central hubs was brown. Intuitively, the centre would appear white under the dermoscope if the incident light could not pass through the compact orthohyperkeratosis. We have reported that the most common epidermal findings of PCA were hyperkeratosis and irregular acanthosis.[14] Therefore, it was reasonable to find that only a few patients with MA in our study showed 'brown' central hubs and, because hyperkeratosis was a common feature of LA, the colour of the central hubs in all of our patients with LA was white. As the extent of hyperkeratosis became thick and compact, as shown in Figure 2, the central hubs disappeared and were replaced by the 'scar-like' morphology. In some cases of LA showing large papules with extremely thick orthohyperkeratosis, as shown in Figure 3, all the dermoscopic details vanished and only a structureless area was left.

This study has limitations. Firstly, only the macular type and LA were included in this study. Further studies of rare PCA subtypes with dermoscopy are required. Secondly, not all cases underwent skin biopsy to confirm the diagnosis although we recruited only cases with typical clinical presentations of PCA to decrease the chance of misdiagnosis. Thirdly, the data were collected from an Asian population. As the nature of PCA may be different in different ethnic groups, the dermoscopic morphologies of PCA may differ as well.

In conclusion, this study served to show that there are dermoscopic features characteristic of PCA. The most common finding is a brown or white central hub surrounded by various configurations of pigmentation. In addition to history and physical examination, dermoscopy may assist in achieving an accurate diagnosis of PCA.

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