In vitro differential diagnosis of clavus and verruca by a predictive model generated from electrical impedance.
BACKGROUND
Similar clinical appearances prevent accurate diagnosis of two common skin diseases, clavus and verruca. In this study, electrical impedance is employed as a novel tool to generate a predictive model for differentiating these two diseases.


METHODS
We used 29 clavus and 28 verruca lesions. To obtain impedance parameters, a LCR-meter system was applied to measure capacitance (C), resistance (Re), impedance magnitude (Z), and phase angle (θ). These values were combined with lesion thickness (d) to characterize the tissue specimens. The results from clavus and verruca were then fitted to a univariate logistic regression model with the generalized estimating equations (GEE) method. In model generation, log ZSD and θSD were formulated as predictors by fitting a multiple logistic regression model with the same GEE method. The potential nonlinear effects of covariates were detected by fitting generalized additive models (GAM). Moreover, the model was validated by the goodness-of-fit (GOF) assessments.


RESULTS
Significant mean differences of the index d, Re, Z, and θ are found between clavus and verruca (p<0.001). A final predictive model is established with Z and θ indices. The model fits the observed data quite well. In GOF evaluation, the area under the receiver operating characteristics (ROC) curve is 0.875 (>0.7), the adjusted generalized R2 is 0.512 (>0.3), and the p value of the Hosmer-Lemeshow GOF test is 0.350 (>0.05).


CONCLUSIONS
This technique promises to provide an approved model for differential diagnosis of clavus and verruca. It could provide a rapid, relatively low-cost, safe and non-invasive screening tool in clinic use.
Institute of Biomedical Engineering, National Taiwan University, Taipei, Taiwan.
Chien-Ya
CY
Hung
Department of Dermatology, Mackay Memorial Hospital, Taipei, Taiwan.
Pei-Lun
PL
Sun
Institute of Zoology, National Taiwan University, Taipei, Taiwan.
Shu-Jen
SJ
Chiang
Institute of Biomedical Engineering, National Taiwan University, Taipei, Taiwan.
Fu-Shan
FS
Jaw
D019540:Area Under Curve; D002145:Callosities / Q000175:diagnosis* / Q000473:pathology; D003937:Diagnosis, Differential; D017097:Electric Impedance; D006801:Humans; D016015:Logistic Models; D012372:ROC Curve; D014860:Warts / Q000175:diagnosis* / Q000473:pathology