Capillary density in patients with systemic sclerosis, as determined by microscopy counts and compared with computer-based analysis

Objective To develop a method enabling capillary density to be determined rapidly and accurately in patients with systemic sclerosis. Method Capillary density was determined in II controls and 22 patients: 5 with dif fuse cutaneous systemic sclerosis (dSSc), 12 with limited cutaneous systemi c sclerosis (ISSc), two with suspected systemic sclerosis (suspSSc), 2 with sclerodermatomyositis, and one with undifferentiated connective tissue dis ease. Using a microscope equipped with a graticule, nailfold capillaries we re counted within a 3 mm length of the nailfold; these counts were made by 4 different observers. The results were compared with the corresponding val ues obtained by the computer-based analysis of photographs. Results The median capillary density according to the direct counts was 8.0 loops/ mm (6.7 - 10.0) in the controls, 6.0 loops/mm (range 4.8 - 8.8) in the dSSc subgroup, 5.6 loops/mm (4.2 - 6.5) in the ISSc subgroup, and 7.2 loops/mm (6.2 - 8.2) in the suspSSc subgroup. In the series as a whole there was no significant difference between the median values for the left hands and tho se for the right hands, nor between the median value for all digit IVs and the median value for all four digits analysed (II, III, IV and V). Interobs erver variation was small between the 4 different observers. Direct microsc opy counts were slightly higher than the corresponding values obtained by c omputer-based analysis. Conclusion Direct microscopy counting is a rapid, simple, and reliable means of determ ining capillary density for screening purposes.