Investigation of using very high‐frequency ultrasound in the differential diagnosis of early‐stage pemphigus vulgaris vs seborrheic dermatitis

BACKGROUND: Early‐stage pemphigus vulgaris (PV) often manifests as erythema alone. We hypothesized that very high‐frequency ultrasonography (VHFUS) features could simplify the differential diagnosis of early‐stage pemphigus vulgaris versus seborrheic dermatitis (SD). MATERIALS AND METHODS: Fourteen patients with SD or early‐stage PV were recruited from our outpatient clinic during 2016‐2019. We used 50‐MHz VHFUS to image the erythema on the patients’ scalp, face, chest, and back and retrospectively evaluated their ultrasonographic features. RESULTS: Very high‐frequency ultrasonography images of early‐stage PV showed enhanced epidermal echo (8/14, 57%), linear or oval intra‐epidermal hypoechoic/anechoic areas (12/14, 86%), linear anechoic areas at the dermal‐epidermal junction (14/14, 100%), reduced echo of superficial to whole dermis (9/14, 64%), and slightly increased dermal thickness (14/14, 100%). The intra‐epidermal hypoechoic/anechoic bands (100%) showed the greatest specificity. VHFUS images of SD showed enhanced epidermal echo (7/14, 50%), epidermal unevenness (7/14, 50%), linear anechoic bands at the dermal‐epidermal junction (8/14, 57%), reduced middle dermis echo (10/14, 71%), and slightly increased dermal thickness (10/14, 71%). The epidermal unevenness (100%) had the greatest specificity. There was a significant difference (P < .05) between early‐stage PV and SD regarding the proportion of linear intraepithelial hypoechoic/anechoic bands and linear anechoic areas at the dermal‐epidermal junction. CONCLUSIONS: Early‐stage PV and SD have relatively specific VHFUS erythematous manifestations. Intra‐epidermal hypoechoic/anechoic bands for early‐stage PV and epidermal unevenness for SD were most specific. VHFUS contributes to the differential diagnosis of PV and SD by highlighting their features, that is, intra‐epidermal hypoechoic/anechoic bands and linear anechoic areas at the dermal‐epidermal junction.