The Application of Fluorescence Optical Imaging in Systemic Sclerosis

[Can rheuma be scanned? : Review of the current study situation on fluorescence optical imaging]

BACKGROUND

The novel technique of indocyanine green (ICG)-based fluorescence optical imaging (FOI) using the Xiralite® system (Rheumascan) has been the subject of many different studies worldwide since approval for clinical use in the European Union (2009), USA (2014) and Asia. The FOI depicts the disturbed microcirculation in the joints of both hands caused by inflammation.

OBJECTIVE

The aim of this article is to provide an overview of the current state of studies on ICG-based FOI in different rheumatologic indications.

METHODS

A narrative literature review of publications on ICG-based FOI in the diagnosis of various inflammatory rheumatic joint diseases since 2010 is presented, its use in treatment monitoring is explained, and its value in systemic sclerosis is outlined.

RESULTS

In summary, studies have extensively demonstrated the accuracy of FOI in inflammation detection. Therefore, it can be concluded that FOI is a good supplement to existing imaging modalities. Due to characteristic patterns of both skin and nails, FOI is an indicated procedure especially in psoriatic arthritis and can be very helpful in the diagnostic process in early undifferentiated arthritis. The FOI has shown its usefulness in children (juvenile idiopathic arthritis), for monitoring the course of treatment, and for demonstrating disturbed microcirculation in patients with systemic sclerosis.

CONCLUSION

The presented data imply that FOI should be considered as a valuable complementary imaging tool in the diagnostic algorithm of daily rheumatologic practice, both for diagnosis and for follow-up monitoring. In particular, the automated analyses should be able in the future to objectify measurements of inflammatory activity as well as monitoring the response to treatment.

Fluorescence optical imaging: ready for prime time?

The novel technique of fluorescence optical imaging (FOI, Xiralite), which is approved in the European Union and the USA for clinical use, has been the object of studies since 2009. Indocyanine green-based FOI can demonstrate an impaired microcirculation caused by inflammation in both hands in one examination. Several studies have investigated FOI for detection of joint inflammation by comparing FOI to magnetic resonance imaging (MRI) and/or musculoskeletal ultrasound (MSUS). The results have shown a generally good agreement (>80%) between FOI and clinical examination, MRI and MSUS by power Doppler in inflammatory joint diseases. Moreover, characteristic enhancements in skin and nails are seen in PsA, which potentially can be useful in the diagnostic process of early undifferentiated arthritis. Furthermore, FOI has been investigated for the visualisation of a disturbed microcirculation in the hands and fingers of patients with systemic sclerosis (SSc), highlighting the potential of monitoring vascular changes in SSc and other vasculopathies. The available data indicate that it is time to consider FOI as a useful part of the imaging repertoire in rheumatology clinical practice, particularly where MSUS and MRI are not easily available.

Detection of subclinical skin manifestation in patients with psoriasis and psoriatic arthritis by fluorescence optical imaging

OBJECTIVES

To investigate the frequency of subclinical skin inflammation in both hands by fluorescence optical imaging (FOI) in patients with psoriasis/psoriatic arthritis (Pso/PsA) vs. rheumatoid arthritis (RA) and healthy individuals, and to correlate these findings with cardiovascular (CV) risk factors.

PATIENTS AND METHODS

The FOI scans were analyzed retrospectively to detect clinically invisible skin enhancement (0-3 scale) in both hands without relationship to underlying joints or blood vessels. We further characterized the FOI patterns and sorted the scans into groups based on the assumed diagnosis (Pso/PsA, RA, and healthy controls), which was compared with the physician's diagnosis. Furthermore, the associations between CV risk factors and imaging findings were investigated by regression analyses.

RESULTS

We included FOI scans of patients with Pso/PsA (n = 80), RA (n = 78), and healthy controls (n = 25). Subclinical skin enhancement on the back of their hands was more common in Pso/PsA (72.5%) than in RA patients (20.5%) and healthy individuals (28.0%) (p < 0.001). Based on the FOI pattern, the majority of patients with Pso/PsA (72.5%), RA (76.9%), and healthy controls (68.0%) were classified correctly using the physician-based diagnosis as reference (overall agreement of 74%, kappa = 0.57). No CV risk factors except body weight (kg) were associated with subclinical skin enhancement (OR 1.04, 95% CI 1.02-1.06; p < 0.001).

CONCLUSION

Subclinical subdermal skin inflammation was common in Pso/PsA patients using FOI. Based on the FOI pattern, most patients with Pso/PsA and were classified with the correct diagnosis. We demonstrated an important influence of the body weight on our FOI results. FOI may be a helpful novel tool to study microcirculation in rheumatic diseases with skin involvement.

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.

Fibrosis imaging: Current concepts and future directions

Fibrosis plays an important role in many different pathologies. It results from tissue injury, chronic inflammation, autoimmune reactions and genetic alterations, and it is characterized by the excessive deposition of extracellular matrix components. Biopsies are routinely employed for fibrosis diagnosis, but they suffer from several drawbacks, including their invasive nature, sampling variability and limited spatial information. To overcome these limitations, multiple different imaging tools and technologies have been evaluated over the years, including X-ray imaging, computed tomography (CT), ultrasound (US), magnetic resonance imaging (MRI), positron emission tomography (PET) and single-photon emission computed tomography (SPECT). These modalities can provide anatomical, functional and molecular imaging information which is useful for fibrosis diagnosis and staging, and they may also hold potential for the longitudinal assessment of therapy responses. Here, we summarize the use of non-invasive imaging techniques for monitoring fibrosis in systemic autoimmune diseases, in parenchymal organs (such as liver, kidney, lung and heart), and in desmoplastic cancers. We also discuss how imaging biomarkers can be integrated in (pre-) clinical research to individualize and improve anti-fibrotic therapies.

Disturbed microcirculation in the hands of patients with systemic sclerosis detected by fluorescence optical imaging: a pilot study

BACKGROUND

Utilising fluorescence optical imaging (FOI), the distribution of an intravenously applied colouring agent indocyanine green (ICG) can be analysed with the potential to identify malperfusion by little to no tissue enhancement. Systemic sclerosis (SSc) is characterised by the presence of digital ulcers reflecting progressive vasculopathy. The objective was to investigate the potential of FOI in the detection of disturbed microcirculation in the hands and fingers of patients with SSc and to link FOI findings to clinical signs of ischemia such as digital ulcers and pitting scars.

METHODS

In this cross-sectional study, 63 patients with SSc and 26 healthy subjects were examined. FOI was performed in all 89 individuals and compared to clinical data and capillaroscopic findings assembled for the SSc cohort.

RESULTS

Healthy subjects showed initial ICG signals in their fingertips in 93.6%, SSc patients in 78.5% (limited SSc) and 43.2% (diffuse SSc). Moreover, in SSc patients, FOI findings were significantly associated with a late capillaroscopic pattern, disseminated SSc features, a diffuse SSc subtype, and the presence of digital ulcers or pitting scars. Intra- and inter-reader reliability for FOI amounted to κ = 0.786 and κ = 0.834, respectively.

CONCLUSIONS

FOI is able to detect areas of reduced microcirculation in patients with SSc with high association to capillaroscopic findings. The results pave the way for future FOI investigations into its role in the prediction of complications due to an impaired acral perfusion.