Nailfold Capillaroscopy in Diabetes Mellitus: Potential Technique for the Microvasculature Evaluation

The capillary loop consists of an arterial or afferent branch and a venous or efferent branch. The main parameters to be evaluated are: length, diameter, density, venous plexus and morphological abnormalities. These elements should be evaluated in the distal row or near the nailfold. The normal number of capillaries per millimeter is from seven to twelve arranged in an inverted U-shape (Figure 1).

Research methods of the capillaries have varied through the years, from the use of stereomicroscopes with magnification of 10-100X for the visualization of the entire nailfold area [5] to new semiautomatic methods for the visualization of the capillaries with an innovative television system [6].
Other optical methods such as ophthalmoscopes and dermatoscopes were also used. Currently, for the observation of capillaries it is used the videocapilaroscopy that consists of a combination of a microscope and a digital recorder that provides a magnification of 50-100X.
The indications for capillaroscopy are: Evaluation of patients with Raynaud's Phenomenon, differential diagnosis of collagenopathies, primary diagnosis of scleroderma, diseases that compromise the capillary microarchitecture, like diabetes mellitus [7,8].
The dermal papillae are located perpendicularly to the cutaneous surface. The capillary arrangement at the nailfold level is located in a parallel or oblique way in relation to the cutaneous plane, in two or three layers.
The capillary loop consists of an arterial or afferent branch and a venous or efferent branch. The main parameters to be evaluated are: length, diameter, density, venous plexus and morphological abnormalities. These elements should be evaluated in the distal row or near the nailfold. The normal number of capillaries per millimeter is from seven to twelve arranged in an inverted U-shape ( Figure 1).
Recent studies conclude that capillaroscopy provides key data for the determination of vascular damage in diabetic patients and thus, allows the evaluation of the progression of the disease [9], making this technique a potential future utility in the microvascular disease evaluation. Maldonado et al. demonstrated that the use of capillaroscopy in patients with diabetes allows the identification of capillaroscopic abnormalities, possibly including a characteristic pattern in this group of patients consisting of tortuous, cross-linked capillaries, avascular zones and ectasias, also the study showed an association between microangiopathies seen at the ophtalmoscopy and the presence of ramified capillaries and avascular zones seen at the nailfold level [1] ( Figure 2).  Barchetta studied the possible relationship of microangiopathic lesions detected in retinal vessels and capillary changes in patients with type I and type II diabetes [10]. It was observed that these patients had a greater capillary diameter, ectasias and nailfold edema, in contrast with healthy subjects [10].

Endocrinology & Metabolic Syndrome
Uyar et al. studied a population of patients diagnosed with diabetes mellitus and evidenced large capillaroscopic changes such as: tortuous capillaries, ramified, increased capillary diameter, compared to the control group. In addition, in patients with diabetic retinopathy, these alterations were increased [11].
Maldonado et al. found an association between microangiopathies at the fundoscopy and capillaroscopic alterations such as ramified capillaries and avascular zones [1]. Chang et al. also found a correlation between diabetic retinopathy and the presence of tortuous, ramified capillaries and capillary dilatation, in addition to confirming that these alterations are increased with the severity of diabetic retinopathy [3].
These patterns demonstrate that a microvascular component exists in the pathophysiology of diabetic retinopathy and capillaroscopy is a tool that can accurately detect capillaroscopic changes and relate them to systemic vascular complications.
Focusing in the metabolic control, chronic hyperglicemia affect the capillary endothelia, generating microvascular architecture changes [12], that can be evidenced by the use of capillaroscopy [13,14]. Also the disease evolution has shown that can contribute to capillaroscopy changes, Kuryliszyn et al. found an escalating appearance of ramified capillaries in diabetic patients with a prolonged evolution time (of more than 10 years) [9]. Bollinger et al. showed similar data, in which they described more capillaroscopic alterations in diabetic patients with a disease evolution of over 10 years [5].
However, the main limitation remains in the small number of articles focusing on the qualitative findings and relationship with markers of disease progression yet to be established. Since the capillaroscopy is a potential future utility in the evaluation of microvascular, there is a need of more research in this field.