Technique clinical findings and prognostic value of NCM
Along with the retina, the nailfold represents one of the only sites in the body where direct visualization of the vasculature is possible. NCM involves the placement of a drop of immersion oil or surgical lubricant on the cuticle of one or more digits (usually the ring or middle fingers), and visualization of the capillaries through a magnifying device (an ophthalmoscope set at 40 diopters, dermatoscope, stereomicroscope, or digital video capillaroscopy).
The normal nailbed demonstrates a confluent distribution of fine capillary loops. Dilated tortuous capillary loops and areas of avascularity (“dropout”) are often demonstrated in patients with underlying rheumatologic diseases such as SSc, dermatomyositis, and mixed connective tissue disease.
Up to 1% of patients initially diagnosed with primary RP will transition to a connective tissue disease (commonly limited SSc) each year. A large prospective cohort study demonstrated that only 2% of patients with a normal NCM and negative SSc-antibodies (Scl70, CENP, RNA pol III or Th/To) developed subsequent SSc. In contrast, 80% of those with an abnormal NCM (vessel dropout and dilation) and a positive SSc-antibody went on to develop SSc. The presence of either an abnormal NCM or SSc-antibody was associated with progression to SSc in 30% of patients. NCM was more strongly associated with progression to SSc than antibody presence.
