We thank Sulli and colleagues  for their interest in our article entitled 'Comparison of laser Doppler imaging, fingertip lacticemy test, and nailfold capillaroscopy for assessment of digital microcirculation in systemic sclerosis' , which was published in a recent issue of Arthritis Research & Therapy. Sulli and colleagues commented on our results regarding the lack of correlation between the laser Doppler imaging (LDI) technique and nailfold capillaroscopy (NFC) and raised interesting questions.
We totally agree with the comment that NFC is a powerful tool for the assessment of microvascular damage in systemic sclerosis (SSc). Recently, we showed a positive correlation between NFC abnormalities and the extent of cutaneous and visceral involvement in SSc patients, confirming that NFC is a relevant approach not only for diagnosis but also for the evaluation of the extension and severity of SSc . However, NFC evaluates only the morphological aspect of SSc vasculopathy, and complementary tools are used, with different results, in many studies for the evaluation of functional aspects of peripheral vascular disease .
Sulli and colleagues mentioned three interesting, recently published papers [5–7] with results different from those of our paper. However, different methods for the evaluation of blood perfusion were used in each of them, and it is difficult to compare results obtained with different techniques. Cutolo and colleagues  assessed fingertip blood perfusion by laser Doppler flowmetry, and Mugii and colleagues  evaluated red blood cell velocity by means of videocapillaroscopy. We emphasize that only Rosato and colleagues , who were considered in our original paper, evaluated blood perfusion by means of LDI. Moreover, the mechanisms involved in SSc vasculopathy are complex, and controversial findings are not surprising. Th e LDI method used in our original study is considered the most promising tool for the study of microvascular blood flow. In our study, LDI showed lower digital blood flow in SSc patients when compared with healthy controls and correlated negatively with fingertip lacticemy, allowing objective measurement of blood perfusion. It is also relevant to point out that Murray and colleagues  showed only a weak correlation between intercapillary distance measured by NFC and the blood flow also measured by LDI. As in our study, the authors could not find any other correlation between other NFC parameters and LDI.
Therefore, it is appropriate to consider that different techniques such as LDI (dynamic changes) and NFC (morphology changes) complement one another. Of course, further studies with a larger sample of patients assessed by the same technique are required to evaluate possible discrepancies between different studies.
laser Doppler imaging
Our study was supported by the State of São Paulo Research Foundation (FAPESP grant 06/59073-3) and partially by the Brazilian Society of Rheumatology Research Agency.
Rheumatology Division, Department of Medicine, Universidade Federal de São Paulo
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