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 11 controls and 22 patients: 5 with diffuse cutaneous systemic sclerosis (dSSc), 12 with limited cutaneous systemic sclerosis (lSSc), two with suspected systemic sclerosis (suspSSc), 2 with sclerodermatomyositis, and one with undifferentiated connective tissue disease. Using a microscope equipped with a graticule, nailfold capillaries were counted within a 3 mm length of the nailfold; these counts were made by 4 different observers. The results were compared with the corresponding values obtained by the computerbased 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 lSSc 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 those 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). Interobserver variation was small between the 4 different observers. Direct microscopy counts were slightly higher than the corresponding values obtained by computer-based analysis. CONCLUSION: Direct microscopy counting is a rapid, simple, and reliable means of determining capillary density for screening purposes.