Differences among Dermoscopic Findings in Riehl's Melanosis of the Cheek and Neck.

Dear Editor:

Riehl's melanosis is a pigmented dermatosis that presents as bilateral, symmetrical, grayish-purplish-brown reticulated hyperpigmentation on the face and neck1. The etiology of Riehl's melanosis remains largely unknown, but it is believed to be associated with contact dermatitis or photo-contact dermatitis caused by ingredients from certain cosmetics2. The diagnosis of Riehl's melanosis may be difficult because the diagnostic criteria have not been clearly established. Recently, dermoscopy has been widely used for the accurate diagnosis of pigmented skin lesions. Wang and Xu3 explained that pseudonetwork and grey dots/granules were the most suggestive dermoscopic features of Riehl's melanosis on the face. However, the face and neck have different skin characteristics, and skin lesions of Riehl's melanosis can also be found on the lateral side of the neck in some patients.

In this retrospective study, we compared dermoscopic findings of the face and neck in patients with Riehl's melanosis seen at the Department of Dermatology of Kyung Hee Medical Center (Seoul, Korea) from June 2014 to April 2017. The Ethics Committee of Kyung Hee Medical Center approved the study (approval number: KHMC IRB 2019-06-021). All patients were previously diagnosed with Riehl's melanosis and we reviewed clinical charts and obtained baseline clinical images and dermoscopic images. We have included only those patients who had dermoscopic images of both the face and neck. Digital dermoscopic images of the lesions were obtained using a Dermlite DL3 with polarized light (3Gen Inc., San Juan Capistrano, CA, USA) (10-fold magnification) mounted on a Canon EOS 350D camera (Canon Corp., Tokyo, Japan). We received the patient's consent form about publishing all photographic materials. Seven main dermoscopic features were evaluated, namely, slight scales, pseudonetwork, grey dots/granules, follicular keratotic plugs, perifollicular whitish halo, telangiectatic vessels and hypopigmented network patterns.

A total of 9 patients with Riehl's melanosis were identified and included in this study. Among the patients, eight were female and one was male, and the mean age at the time of inclusion was 62.9 years. The pigmentation presented on the entire face, but it was more pronounced on the lateral face and extended to the lateral side of the neck (Fig. 1). None of the patients were treated prior to the baseline visit and most patients had no history of preceding pigmentary dermatosis, inflammatory dermatosis or atopic dermatitis. The demographic data and dermoscopic features of our study patients are summarized in Table 1 and illustrated in Fig. 1. In the dermoscopic images of the face, pseudonetwork, grey dots/granules and telangiectatic vessels were observed in all the patients (9/9, 100.0%), while slight scales, follicular keratotic plugs and perifollicular whitish halo were observed in 6 of 9 patients (6/9, 66.7%). And erythematous background was observed in 5 of 9 patients (5/9, 55.6%). In the cheek, a hypopigmented network pattern was not observed in any patient. In the dermoscopic images of the neck, pseudonetwork, grey dots/granules and telangiectatic vessels as well as slight scales and hypopigmented network pattern were observed in all the patients (9/9, 100.0%). On the other hand, follicular keratotic plugs and perifollicular halo were observed only in one and 3 of 9 patients, respectively, at a lower rate than in the face.

Fig. 1

Baseline clinical images of a 58-year-old female (A, B) and representative dermoscopic images of the face (C) and neck (D). The pigmentation presented on the entire face, but it was more pronounced on the lateral face and extended to the lateral side of the neck. In the face, pseudonetwork, grey dots/granules and telangiectatic vessels were prominently observed. In the neck, a characteristic hypopigmented network pattern (black arrow) with slight scales was observed.

Table 1

Demographic data and dermoscopic features of the study patients

	Sex	Age (yr)	Slight scales		Pseudo network		Grey dots/granules		Follicular keratotic plugs		Perifollicular whitish halo		Telangiectatic vessels		Hypopigmented network pattern		Erythematous background
			Face	Neck	Face	Neck	Face	Neck	Face	Neck	Face	Neck	Face	Neck	Face	Neck	Face	Neck
1	Male	64	+	+	+	+	+	+	+	−	+	−	+	+	−	+	+	+
2	Female	58	+	+	+	+	+	+	+	−	+	−	+	+	−	+	−	−
3	Female	61	−	+	+	+	+	+	−	+	−	+	+	+	−	+	−	−
4	Female	64	−	+	+	+	+	+	+	−	+	−	+	+	−	+	+	+
5	Female	59	+	+	+	+	+	+	−	−	−	−	+	+	−	+	+	+
6	Female	58	−	+	+	+	+	+	−	−	−	−	+	+	−	+	+	−
7	Female	71	+	+	+	+	+	+	+	−	+	−	+	+	−	+	−	−
8	Female	65	+	+	+	+	+	+	+	−	+	+	+	+	−	+	−	−
9	Female	66	+	+	+	+	+	+	+	−	+	+	+	+	−	+	−	−
Frequency (%)			66.7	100.0	100.0	100.0	100.0	100.0	66.7	11.1	66.7	33.3	100.0	100.0	0.0	100.0	44.4	33.3

+ and − represent present and absent features, respectively.

The major histopathologic features of Riehl's melanosis are vacuolar degeneration of the basal layer and pigment incontinence of the dermis4. These pathological features correspond with grey dots/granules on the dermoscopic images that represent melanophages in the dermis5. The pseudonetwork is due to homogeneous pigmentation that is interrupted by the non-pigmented follicular openings5. In this study, we also confirmed grey dots/granules and pseudonetwork in all cases the same as in the previous study3. However, the dermoscopic features of Riehl's melanosis in the neck showed different patterns compared with the face. In the neck, slight scales and a hypopigmented network pattern were observed additionally in all patients while follicular keratotic plugs and perifollicular halo were not observed significantly compared to the face. The flour-like slight scales were a specific finding to Riehl's melanosis because this pattern was not observed with other hyperpigmented disorders and this dermoscopic feature was more prominently observed in the neck3. The majority of Riehl's melanosis occurs in middle-aged women. In the neck, the number and depth of wrinkles increased with age because of intrinsic and extrinsic aging processes6. Furthermore, we repeatedly raise, lower, and turn our head in everyday life. Therefore, the skin of the neck needed a lot of flexibility. Skin grooves are deeper and anisotropy of skin furrows are more complex in the neck compared to the face. A recent study by Kim et al.7 reported that neck wrinkles increased with age and were five-fold deeper than those of the cheek. Therefore, these furrows are relatively spared from contact allergens and sun exposure. We suppose that this could be the cause of the hypopigmented network pattern on the dermoscope. These results suggest that the pathogenesis of Riehl's melanosis is contact dermatitis or photo-contact dermatitis. A perifollicular whitish halo corresponds with perifollicular fibrosis in histopathology8. In the neck, a perifollicular whitish halo and follicular keratotic plug were observed in fewer cases compared to the face. We hypothesize that this is caused by the higher hair follicle density of the face compared to the neck. These dermoscopic findings can help to differentiate Riehl's melanosis from other diseases that may cause hyperpigmentation in the neck. In Terra Firma-Forme dermatosis, hyperpigmentation of stone pavement pattern can be seen with patchy distribution rather than diffuse distribution. And dirty neck in atopic dermatitis shows hyperpigmentation of deeper rippled pattern with prominent scales.

In this study, we were able to determine that pseudonetwork and grey dots/granules were the most suggestive dermoscopic features of Riehl's melanosis. In the neck, we observed a hypopigmented network pattern with slight scales and these findings are thought to be helpful in diagnosis of Riehl's melanosis. However, our study had some limitations because of the relatively small number of patients and the retrospective study design. Therefore, further studies are needed to improve the dermoscopic diagnosis of Riehl's melanosis.