Retro-Dermoscopy, A Useful Technique to Detect Clues of Seborrheic Keratosis.

Sir,

The diagnosis of seborrheic keratosis (SK) may sometimes be challenging, and “retro-dermoscopy,” consisting of the video dermoscopy of the rear side of the shaved biopsies, may prove helpful.[1] We believe that it eases the detection of some features that are not visible on normal dermoscopy.

To evaluate the technique, from November 2020 to January 2021, we collected 13 cutaneous neoformations, each from a different patient, for which a definitive clinical-dermoscopic diagnosis of SK was not possible.

We included the lesions showing unclear margins, absence of the typical ridges or fissures on the surface, lack of multiple colors, and absence of comedo-like openings and of milia like-cists on dermoscopy. Moreover, we considered the following criteria: the presence of atypical vessels, pigmented pseudo-network, and a history of recent traumas.

We performed a shave biopsy of the lesions by using a 15-inch blade after injecting local mepivacaine. The specimens were then washed with a physiological solution and turned upside down on sterile gauze. Then, we performed the retro-dermoscopy to highlight milia-like cysts, comedo-like openings, and the absence of melanocytic patterns of pigmentation [Figure 1]. All specimens were then sent to histopathological examination to confirm the diagnosis.

Figure 1

Classical and retro-dermoscopy of some of the excised lesions. (A) Classical frontal dermoscopy of the lesions; note the absence of many of the typical characteristics of seborrheic keratoses, such as the presence of ridges on the surface, clearly visible milia-like cysts, and pseudo-homogeneous pigmentation (×20). (B) After cleansing and before inclusion in formalin: yellow arrows highlight the milia-like cysts, whereas red arrows highlight the comedo-like openings (×20)

In our case series, the lesions did not show the “classical” clinical-dermoscopic features of SK at the initial evaluation.[2] However, the absence of a clear pigment network, the raised margins, the greasy surface, the patients’ age, and the presence of other “typical” SKs on the patients’ skin clinically favored this diagnosis.[2]

After performing shaving biopsy and retro-dermoscopy, most of the lesions showed, compared to straight dermoscopy, comedo-like openings (0 vs. 8; P = 0.001); all the neoformations showed the absence of melanocytic patterns of pigmentation (6 vs. 0; P = 0.008) and the presence of multiple milia-like cysts (13 vs. 2; P = 0.001) [Table 1].

Table 1

Clinical, demographic, and dermoscopic characteristics of the collected cases

Clinical data
Number of lesions	13
Mean age of patients at diagnosis	66 (Std. dev 12,507)
M:F	9:4
Locations	Face: 1 Back: 3 Axilla: 1 Leg: 3 Chest: 5
	Straight dermoscopy	Retro-dermoscopy	Statistical analysis (P)
Features
Fissurations and/or ridges on the surface	7	0	0.001
Peripheral telangiectasias	2	0	0.175
Vessels	7	0	0.003
Hairpin vessels	6	0	0.008
Linear irregular vessels	1	0	0.337
Comedo-like openings	0	8	0.001
Milia-like cysts	2	13	0.001
Moth-eaten borders	2	1	0.337
Sharp demarcation	5	6	0.337
Network-like structures	6	0	0.008
Homogeneous pigmentation	6	9	0.082
Multiple colors	7	4	0.165

Finally, all the lesions excised were histopathologically confirmed as SKs.

When the shave technique is preferred, both for ease in terms of costs and of execution in the outpatient setting,it allows to perform the retro-dermoscopy techinque. We believe that this approach may allow the detection of some of the typical features of SKs on their dermal side. These features (especially comedo-like openings and milia-like cysts) might be difficult to observe on “classical” dermoscopy due to marked acanthosis or local traumas.[2] The rationale is that retro-dermoscopy may better highlight those structures that would otherwise be covered by the excessive thickness or traumatization of the epidermal surface.[2]

Diagnosis of SK is not always easy as some lesions may be traumatized and present unusual clinical-dermoscopic characteristics at the onset. Even when the clinical presentation suggests a benign diagnosis, the absence of clear pathognomonic signs must lead to a cautious attitude; therefore, a histopathological confirmation may be required.

Still, our results show that retro-dermoscopy may be a useful additional tool to address an initial diagnosis of SK.

Authors’ contributions

All authors contributed equally to the manuscript and read and approved the final version of the manuscript.

Congresses: Congresso Nazionale SIDeMaST 2021 “LA RETRO-DERMATOSCOPIA DELLE CHERATOSI SEBORROICHE”

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.