The "green nail" phenomenon in ICG-enhanced fluorescence optical imaging - a potential tool for the differential diagnosis of psoriatic arthritis.

BACKGROUND AND OBJECTIVES: Early diagnosis of psoriatic arthritis poses a particular challenge. A novel fluorescence optical imaging technique, the Xiralite® system is very useful in this regard as it allows for visualization of microvasculature and perfusion. The present study is the first to systematically examine fluorescence optical signals in a large psoriatic arthritis cohort.

PATIENTS AND METHODS: In the primary study, we reviewed and analyzed extra-articular fluorescence optical signal patterns in 241 imaging sequences obtained from 187 psoriatic arthritis patients; 36 fluorescence optical sequences from 31 patients with rheumatoid arthritis served as controls. In a follow-up study, 203 consecutive fluorescence optical sequences from 54 psoriatic arthritis patients and 149 control subjects with various inflammatory rheumatic disorders were retrospectively evaluated in order to validate the primary study results in terms of the patterns previously identified.

RESULTS: Psoriatic arthritis patients exhibited three different fluorescence optical signal patterns in projection of the nails that have not been previously described. One of these patterns was the "green nail" sign, which was highly specific (97 %) for psoriatic arthritis. In the follow-up study, the specificity of this phenomenon in psoriatic arthritis was 87 % in comparison to the control cohort.

CONCLUSIONS: In the present study, fluorescence optical signals in the nail region proved to be highly specific for psoriatic arthritis. The "green nail" phenomenon seems to be of particular diagnostic interest as a potential sign of impaired microcirculation of the nail bed.