**Abstract**

Nailfold capillaroscopy (NFC) is a simple, validated, and noninvasive method to assess the microcirculation, through direct visualization of the capillaries. Main patterns are classified, according to Cutolo et al., as scleroderma, further divided into early, active, or late patterns, or nonscleroderma. NFC findings include dilated loops, tortuosities, meandering or bushy capillaries, hemorrhage, or architectural distortion. NFC use has been indicated for the evaluation of Raynaud's phenomenon (RP), once it permits the distinction between primary and secondary RP. NFC results accounts for diagnostic criteria of systemic sclerosis, but they can also be useful in staging other connective tissue autoimmune diseases, like systemic lupus erythematosus, inflammatory myositis, or vasculitis. The CSURI index uses NFC for prediction of digital ulcer relapse. Recent evidence revealed NFC can also be applied in systemic disorders with vascular involvement.

**Keywords:** nailfold capillaroscopy, microcirculation, Raynaud's phenomenon, connective tissue autoimmune disorders, vasculitides

### **1. Introduction**

Nailfold capillaroscopy (NFC) is a noninvasive, simple, and highly sensitive technique used in the study of microcirculation, as it permits direct visualization of nailfold capillaries [1, 2]. The understanding of NFC results from years of research in Raynaud's phenomenon (RP) in rheumatic diseases. In fact, this method is a paramount tool to differentiate between primary and secondary RP and, associated with autoantibodies, contributes for an early detection of systemic autoimmune connective tissue disorders (AICTD), as microcirculation abnormalities can arise as first manifestations of these diseases [3–5]. Its importance has reached a global recognition and validation as it became a classification criterion for systemic sclerosis, pointing 2 out of a minimum of 9 points to perform the diagnosis [6].

Ensuing studies have been disclosing the relationship between NFC abnormalities and some clinical syndromes or diseases, as digital ulcers, myositis, pulmonary hypertension, heart failure severity, diabetes mellitus, and arterial hypertension, among others [7–13]. Capillaroscopy can also be useful in monitoring the microvascular impact of certain drugs, as systemic vasodilators [2]. A role of NCF as a prognostic tool has been established with the Capillaroscopic Skin Ulcer Risk Index (CSURI), to predict the appearance of new scleroderma ulcers and/or persistence of nonhealing lesions, within 3 months from NFC exam [14]. It has a good sensitivity, specificity, and positive predictive value, even in different devices. Its reliability has been successively demonstrated by European League Against Rheumatism (EULAR) study groups [15–17].

Indications for NFC do not resume to RP or other vascular acrosyndromes approach. It should be performed to any patient with microcirculation involvement from a systemic disease that includes AICTD, like systemic sclerosis, idiopathic inflammatory myositis, mixed connective tissue disease, and systemic lupus erythematosus, among others, but also other systemic diseases associated to microangiopathy, like vasculitides, diabetes, and arterial hypertension. As it also plays an important role in diagnosis, prognosis, and treatment monitoring of some diseases, capillaroscopy can be considered to act as a promising microcirculation biomarker [18].
