Comment on: Micro magnetic resonance angiography of the finger in systemic sclerosis

SIR, The micromagnetic resonance angiography pictures published by Wang et al. [1] have impressive resolution and the scope to provide a quantitative vascular score. The study limitations are considered mainly in terms of the number of study participants and we would like to highlight the importance of measuring environmental control when investigating vasospastic disorders. SSc patients may have a varying degree of vasoconstriction on any one day influenced by environmental factors (e.g. temperature and humidity), or by pharmaceutically active compounds e.g. caffeine, cigarettes, anti-hypertensive and vasodilator therapy. Day-to-day repeatability data on image acquisition are not presented; however, the interpretation of the images acquired has excellent inter-reader agreements.

The digital artery lumen area may vary significantly with vasospasm, e.g. during the vasoconstriction phase of a Raynaud's attack. Indeed RP is almost universally present in SSc and is a key feature of the current classification criteria [2]. In early and evolving pre-SSc [3], vasospasm may predominate over fixed arterial occlusion/stenosis and the correlation between disease duration and digital artery lumen area may not apply to pre-SSc or early-phase SSc disease.

We are currently researching the utility of novel and low-cost multi-site photoplethysmography pulse technology [4] in primary and secondary RP patients, including those pre- and early-phase SSc patients. Here, a key part of our protocol for obtaining repeatable and, therefore, reliable pulse measurements is to undertake the assessment in a dedicated temperature-controlled microvascular measurement facility and with appropriate acclimatization time. May we therefore ask Wang et al. to consider vasospastic factors in any subsequent studies especially when applying the MR technology as they suggest to other vascular disease assessments, e.g. primary RP disease.