Background  Nail psoriasis is a common clinical feature of psoriasis. Accurate examination and evaluation of fingernail psoriasis is an important part of clinical work, however, at present effective methods are lacking.

  Objective  To explore the application value of dermoscopy and 50 MHz high-frequency ultrasound in the examination and evaluation of fingernail psoriasis.

  Methods  Thirty-five patients with nail psoriasis diagnosed at the Department of Dermatology of the First Medical Center of Chinese PLA General Hospital from June 2021 to June 2022 were selected as the case group, and 25 cases without nail-related diseases or family history of psoriasis were selected as the control group. The Nail Psoriasis Severity Index (NAPSI) was used to evaluate the severity of psoriatic fingernails, then the dermoscopic features of psoriatic fingernails were summarized, and the relationship between different dermoscopic characteristics and the severity of fingernail psoriasis was analyzed. The thickness of nail plate and nail bed was measured and compared by ultrasound, and the correlation between the thickness of nail plate and nail bed with the severity of psoriatic fingernails was analyzed.

  Results  The main dermoscopic features were subungual hyperkeratosis, splinter hemorrhages and pitting. The NAPSI of psoriatic fingernails with pitting, crumbling, red spots in the lunula, subungual hyperkeratosis and onycholysis were higher than the fingernails without these features (all P < 0.05). Ultrasound examination showed that the three-layer structure of the psoriatic fingernails plate were not clear, the plate became uneven and subungual hyperkeratosis. The thickness of the psoriatic nail plate and nail bed were thicker than that of the control group. The nail bed thickness was positively correlated with total NAPSI score for all fingers except the left index, middle and ring fingers (r=0.392-0.492, all P＜0.05).

  Conclusion  Dermoscopy can accurately detect and analyze the characteristics of psoriatic fingernails, and can be used as a routine examination method. 50 MHz high-frequency ultrasound can detect the deep changes in the morphological structure of psoriatic fingernails and predict the severity by measuring data, which can be used as a supplement for dermoscopy.