Based on the mainstream adoption of nailfold capillaroscopy as an investigative tool for rheumatologists, a panel of experts in the field of capillaroscopy and microcirculation released a consensus view on the standardization of capillaroscopic image acquisition and analysis, according to a report published in Autoimmune Reviews.
Investigators performed a systematic review of studies focused on different capillaroscopic techniques, capillaroscopic characteristics and definitions, scoring systems, and reliability of image acquisition and interpretation. The panel reached a consensus and developed recommendations for the standardization of capillaroscopy in clinical practice.
Recommendations for Capillaroscopy Equipment
The panel recommended a digital videocapillaroscope with 200× magnification as the gold standard capillaroscopic technique because it is currently the only tool that capillaroscopists with any experience level can use to classify images as scleroderma or nonscleroderma patterns. This recommendation is further based on the high sensitivity, coaxial field illumination of the field, and digital filters of the nailfold videocapillaroscope (NVC).
Since stereomicroscopy and ophthalmoscopy can demonstrate major capillary abnormalities, they have also been proposed as everyday instruments to extend the clinical application use of nailfold capillaroscopy. Digital USB microscopy may be used to perform nailfold capillaroscopy, but should not be used in a research setting because there is no commercial software available for assessing capillary density and dimensions.
Although the panel suggested that the dermatoscope was easier to use than the ophthalmoscope, a greater percentage of dermatoscopy images are not classifiable by software. Smartphones with macrophotography lenses may be used for nailfold capillaroscopy, but are less sensitive than wide-field microscopes in discerning nonscleroderma from scleroderma patterns.
Recommendations for Normality and Abnormality
The panel recommended that clinicians evaluate the following capillary characteristics when assessing for a nailfold capillaroscopic image: capillary density (number of capillaries), capillary morphology (shape of individual capillaries), capillary dimensions (width of apical limb of capillary), and the presence or absence of hemorrhages.
Capillaroscopic patterns in Raynaud phenomenon
According to the researchers, primary Raynaud phenomenon is classified as having a normal capillaroscopy, which is characterized by a normal range capillary density (≥7 capillaries/linear mm), normal capillary morphology (hairpin, tortuous, or crossing shape), normal capillary dimension (width of limbs, <20 µm), absence of confluent bleedings, as well as “nonspecific abnormalities.”
Secondary Raynaud phenomenon because of systemic sclerosis (SSc) was classified by an early scleroderma pattern on nailfold capillaroscopy, specifically a predominance of giant capillaries and no overt loss of capillaries. According to the researchers, active or late scleroderma patterns are characterized by a widening of all segments of the capillary loop, loss of capillaries, disorganization of the nailfold capillary bed, and branched “bushy” capillaries.
Nonspecific abnormalities in Raynaud phenomenon
Nonspecific abnormalities, including lowered capillary density, change in capillary dimension (elongated capillaries, widened loops), prominence of subpapillary plexus, bleedings, or abnormal shapes (bushy capillaries) are not predictive of any defined condition or useful in discerning primary from secondary Raynaud phenomenon; however, giant capillaries and severe capillary loss with abnormal shapes are specific abnormalities characteristic of scleroderma patterns.
Recommendations for Scoring Systems
Qualitative, quantitative, and semiquantitative assessment of nailfold capillaroscopy
In qualitative assessment of NVC, scleroderma patterns are used to distinguish between primary and secondary Raynaud phenomenon; scleroderma patterns are graded as early, active, or late, and these parameters are reliable for diagnosing early SSc.
In quantitative assessment of NVC, capillary characteristics (density, dimension, morphology, and presence or absence of bleeding) are measured per linear millimeter; capillary density is the most reliable parameter for predicting disease progression, and monitoring effects of treatment and capillary diameter is a good indicator of developing early scleroderma patterns.
In semiquantitative assessment, a rating scale is used to score microvascular parameters (0=no changes; 1=<33% of capillary alterations/reduction per linear mm; 2=33%-66% of capillary alterations/reduction per linear mm; 3=>66% of capillary alterations/reduction per linear mm); the rating scale is sensitive enough to monitor progression of microvascular damage because of SSc within the qualitative parameters of scleroderma pattern grades (early, active, and late).
Automated NVC image analysis
Although the development of automated capillaroscopic analysis software is currently ongoing, 2 systems that offer automated methods of quantitative analysis stand out. The Genoa system AUTOCAPI reliably counts the absolute number of capillaries in an operator-selected segment of the nailfold. A fully automated system is also being developed by a group at the University of Manchester that measures 5 quantitative capillaroscopic characteristics and incorporates new parameters of flow, including red blood cell velocity.
Recommendations for Reliability
Reliability is defined as the level of agreement between raters when reporting parameters for common qualitative, semiquantitative, and quantitative measures of nailfold capillaroscopy. The panelists indicated that this inter-rather reliability had excellent image interpretation, specifically the ability of the capillaroscopic technique to discern between scleroderma and nonscleroderma patterns.
Disclosure: Several study authors declared affiliations with the pharmaceutical industry. Please see the original reference for a full list of authors’ disclosures.
Smith V, Herrick AL, Ingegnoli F, et al. Standardisation of nailfold capillaroscopy for the assessment of patients with Raynaud’s phenomenon and systemic sclerosis [published online January 9, 2020]. Autoimmun Rev. doi:10.1016/j.autrev.2020.102458