Most of the data on the NF microvasculature has been obtained from the endrow capillaries, in both morphological and function studies. Only a relatively few studies focus on the total area of NF.
NF endrow capillaries show variations in shape, size, and density even in normal healthy subjects; these variations increase in pathological states. Variation is seen not only between individuals, but also between fingers. Also, within an NF not all capillaries are of the same size and shape. However, over time, in a normal subject, the overall picture of NF capillaries in a given finger has been reported to remain as constant as a fingerprint.
(a) Shape. A normal capillary is usually described as a hairpin-like loop. The deviant capillary loops have been described as tortuous, meandering, branched, bushy, coiled, and so on. Often the same term is used for different shapes and different terms for the same shape by different investigators. (A better definition with adequate illustration should be used to make comparisons of results possible.) These data have been analyzed semiquantitatively by counting the number of deviant capillary loops per NF.
It should be noted here that vigorous "pushing back" of the cuticle during manicure can considerably distort the "normal" U-shaped capillaries at the edge of the NF.
(b) Size. Endrow loops have been classified subjectively as normal, slightly or moderately enlarged, markedly or extremely enlarged, and giant. Measurement data include diameters of arterial and venular limbs of the capillary loop, the caliber of the apical portion, the length of the capillary loop, and the total width of the loop. The ranges for normal measurements reported are arterial, 6 to 19 mm, and venular, 7 to 20 mm.
The problem here is the sampling of capillary loops: Usually they are not all studied. For any measurements, the capillaries have to be sharply focused, but because of technical difficulties this is not always the case. The other selection criteria may be the location within the edge of NF or a subjective preclassification into normal, enlarged, or giant loops.
(c) Density. The density is expressed as number of loops/mm. The normal range is reported as 12 to 17/mm.
(d) Capillary hemorrhages. These are frequently encountered in certain diseases. In normal persons, they are present only in response to obvious injury or microtrauma.
(a) Density. Capillary distribution proximal to the endrow is relatively uniform and can be measured as number of capillaries per mm2. The normal density has been reported as 40 to 50/mm2. A uniform decrease in capillary density in certain conditions can be measured the same way.
(b) Localized loss of capillaries. In some pathological conditions the loss of capillaries is not uniform: There may be an extensive loss, including the endrow and extending to a considerable distance proximally, or there may be discrete areas near the endrow. The loss may be complete, resulting in completely avascular areas, or may be relatively avascular, i.e., showing a few capillary loops but less than 8/mm2. These areas can be measured quantitatively and expressed in mm2.
A semiquantitative scale has also been used: slight, moderate, and extensive. A blind comparison of this scale with quantitative measurement has shown the following: slight 0.4 to 2 mm2, moderate 2 to 4 mm2, and extensive more than 4 mm2 per NF.
Some authors have used the term "drop out" to note the local loss of capillaries. They refer to endrow loops only and require two "dropped-out" loops to define capillary loss or avascularity.
(c) Visibility of subpapillary venous plexus (SPVP). The extent of this feature (SPVP) can be measured by a semiquantitative scale, i.e., the plexus visualization score (PVS). PVS ranges from 0 to 4 per finger and 0 to 40 per subject. Normal range is 0 to 10.
(d) Pattern. The view of the total NF (magnification 12 to 14x) allows us to appreciate the overall pattern of change from the normal one. The loss of capillaries is especially striking and sometimes associated with "bushy formations" (Figure 3 ) near the junction of avascular and normal NF capillary bed.
This total view helps to locate and identify special features to be studied with higher magnification and help to relocate them on serial studies. Observation of the total NF also makes it easier to notice the abnormal appearance of the cuticle: Normally completely transparent, it may show yellow-orange discoloration and varied patterns of outgrowing capillary hemorrhages in the cuticle.
(e) Detection of microinjury. The total NF observation helps to determine whether certain microvascular features are due to local trauma and inflammation rather than related to disease.
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