Particularities of nailfold capillaroscopy in children – literature review

Romanian JouRnal of PediatRics – Vol. lXViii, no. 1, YeaR 2019 ABSTRACT Nailfold capillaroscopy is a simple, non-invasive and low-cost method, that is extremely important in the assessment of adults and children with definite or suspected connective tissue diseases. Peripheral microvascular changes found in nailfold capillaroscopy examination can provide useful information in differential diagnosis and therapy monitoring in majority of connective tissue diseases. Although in adult rheumatology this method has had an incredibly growing interest in the last decades, studies in paediatric population are fewer and generally, the capillaroscopic data used in children are extrapolated from adults. The normal capillaroscopic pattern in the paediatric population has some differences which must be known when performing nailfold capillaroscopy in children.

Regardless of the patients' age, adults or children, during the examination of nailfold capillaries the following aspects are observed and documented: skin transparency -subpapillary venous plexus; capillary distribution, density, dimensions (width and length), and shape (typical hairpin, tortuous, branched, bushy, dilated or giant capillaries); presence of haemorrhages or oedema and sometimes capillary blood flow (22,23,24).
In children as in adults, a normal nailfold capillaroscopic pattern is represented by a parallel and regular disposition of the distal row, capillaries having with the shape of an open hairpin or reversed U letter, with a thinner arm representing the arterial branch and a thicker arm representing the venous branch, and a density of 7-17 per millimetre, with an average of 9 capillary per millimetre (6,7,9,12,15,22,23,24).
The main particularities in children are represented by a greater visibility of the subpapillary venous plexus, a lower number of capillary loops per millimetre and a higher frequency of atypical capillary loops (10,12,13,25).

Nailfold cappilaroscopy parameters
The subpapillary venous plexus is visible at birth and becomes progressively invisible with age, so children have a greater visibility of the subpapillary venous plexus compared to adults (22,24). With ageing, when the skin becomes more trans-parent, the subpapillary venous plexus may become visible again.
Capillary distribution is a capillaroscopic parameter useful in rheumatology clinical practice. In healthy subjects, whether children or adults, the capillary loops have a homogenous, parallel and ordered distribution, with equal distances between the ascending and descending branches (6,12,23,24,25,26).
Capillary density is defined as the number of capillaries over 1 millimetre found in the distal row of each finger and is one of the most important parameters for early diagnosis of people with an underlying risk for connective tissue diseases (2,7,23). Several studies reported that the capillary density is directly influenced by age, younger children having fewer capillaries compared to older children and adults (12,27). In a study of 70 children (17 of them being healthy children) and 20 healthy adults, linear capillary density was significantly higher in healthy adults (mean 8.6 capillaries/mm) compared with healthy children (mean 6.9 capillaries/mm) (12). This tendency of capillary density to increase with age was reported by many authors as a part of the maturation process (12,28). Considering these differences, some authors developed a capillary density scoring system in which they introduced the age as an effective parameter for quantification of the number of capillaries (27).
Reduced capillary density is defined as < 30 capillaries per 5 mm (one nailfold) and avascular area is defined as area where two or more capillaries are missing (6). The scoring systems used for quantification of avascular areas are the same for children as for adults.
Measurement of capillary dimensions includes more parameters but in the daily clinical practice the capillary width and capillary length are the ones usually investigated. There is no consensus regarding the capillary width, different values being reported in the literature. Dolezoleva et al. found a median capillary width of 47 μm in healthy children and 40 μm in healthy adults, concluding that the capillary width is influenced by age, adults and older children having narrower capillaries compared to younger children (12). In adults, the capillary artery diameter greater than 15 μm or that of the venous arm greater than 20 μm is classified as dilated capillary (1,7,23,29). Homogeneous widening of the capillaries having a characteristic horseshoe shape and a diameter greater than 50 μm (0.050 mm) are considered giant capillaries (23). Elongated capillaries are defined as capillary loops longer than 300 μm (0.300 mm) (30). In current clinical practice, qualitative assessments of the capillary dimensions are considered satisfactory while the semi-quantitative assessments find their usefulness in clinical trials.
Some authors reported that 15-34% of healthy adults have abnormal capillaries, such as meandering loops, ectasia, bushy loops and bizarre loops (30,31). In the largest paediatric series, the presence of bushy capillaries has been reported in 6% of healthy children and bizarre capillaries in 27% of healthy children, the authors considering them as a distinct feature of children's capillary network (25). It seems that children of pre-school age have evenly distributed, wide capillaries, with more tortuous, bizarre shapes, compared with adults (12).

Nailfold capillaroscopy in rheumatic disease
Of all connective tissue diseases, systemic sclerosis (SSc) has the most specific capillaroscopic pattern and nailfold capillaroscopy is a key investigation in the diagnosis of this disease (1,8,15). Depending on scleroderma microangiopathy'degree and stage, the scleroderma pattern may be characterized by dilated/giant loops, reduced capillary density/avascular areas, meandering loops, haemorrhages and neo-angiogenesis (1,4,32). Capillary abnormalities observed in juvenile and adult SSc are similar (9,10,34,35). Several studies reported the simultaneous presence of giant capillaries and avascular areas in >60% of children with juvenile SSc (10,34,35). It is reported that, most children with nonspecific capillary abnormalities at the time of juvenile SSc, develop a scleroderma pattern during the course of the disease. (34).
Although a variety of capillaries changes have been reported in 40-90% of adult and juvenile systemic lupus erythematosus (SLE) cases, no specific pattern has been described (9,10,12,38).
Capillaroscopic changes can also be seen in other paediatric rheumatic diseases but they are less striking than those seen in SSc and JDM.

CONCLUSION
The normal appearance of nailfold capillaries in children is similar to adults, the differences being represented by a lower number of capillary loops per millimetre, wider capillaries in young children, a greater visibility of the subpapillary venous plexus and a higher frequency of atypical capillary loops. These differences should be known and considered in assessing the diagnosis of children with rheumatic diseases, especially CTDs.
Typical capillaroscopic patterns found in CTDs are similar in adult and paediatric population.
Nailfold capillaroscopy is not always easy to perform in children and a mandatory condition is a good collaboration with the patient. Paediatric patients may need prolonged accommodation time and more reassuring regarding the pain free procedure.
NFC is a feasible examination in children because it is a simple, non-invasive, low-cost, easy to perform and easy to repeat procedure, being also the best method for microangiopathy evaluation.