The use of fluorescence optical signals in the nail region can be helpful in the differential diagnosis of psoriatic arthritis (PsA). Among 3 different fluorescence optical signaling patterns observed in projection of the nails, one of these, referred to as the “green nail” sign, is highly specific for the detection of PsA, according to the results of a primary cohort study and a retrospective follow-up study published in the Journal of the German Society of Dermatology.
The current study is the first of its kind to systematically examine fluorescence optical signals in a large cohort of patients with PsA. The investigators reviewed and analyzed extraarticular fluorescence optical signal patterns in 241 imaging sequences that were obtained from 187 patients with PsA. A total of 36 fluorescence optical sequences from 31 patients with rheumatoid arthritis served as controls.
A follow-up study was conducted in which a total of 203 consecutive fluorescence optical sequences from 54 patients with PsA and 149 control participants were evaluated retrospectively to confirm the primary study results and validate previously identified patterns.
The detection of “green nails” and the associated “cold nail” sign suggested the presence of microvascular dysfunction of the nail region in patients with PsA. In the primary study, the “green nail” sign was 97% specific for PsA. In the follow-up retrospective study, the specificity of this phenomenon among participants with PsA was 87% when compared with the control cohort.
Major limitations of the current study include its exploratory design, the retrospective use of source data obtained during routine diagnostic workups, and the small size of the control cohort. These weaknesses, in turn, restrict the comparability of the results of this study with those of other similar analyses.
The investigators concluded that the “green nail” phenomenon might be useful in the differential diagnosis of seronegative arthritis. This phenomenon might also be of pathogenic interest as a possible indicator of the presence of impaired microcirculation in the nail bed of patients with PsA.
Wiemann O, Werner SG, Langer HE, Backhaus M, Chatelain R. The “green nail” phenomenon in ICG-enhanced fluorescence optical imaging – a potential tool for the differential diagnosis of psoriatic arthritis. J Dtsch Dermatol Ges. 2019;17(2):138-147.