Retrospective Study of the Clinical Significance of the Neutrophil-to-lymphocyte Ratio in 79 Patients with Palmoplantar Pustulosis

Palmoplantar pustulosis (PPP) is a chronic relapsing inflammatory skin disease characterized by multiple vesicles, pustules, and erythematous plaques on the palms and soles. The exacerbation of PPP is strongly associated with focal infections, such as tonsillitis, dental infections, and sinusitis, in Japan. Recently, the neutrophil-to-lymphocyte ratio (NLR) has been widely used as a convenient and useful marker for clinical conditions and various diseases; however, an association between PPP and NLR has not yet been established. We retrospectively analyzed 79 patients with PPP from our hospital to evaluate the clinical significance of the NLR. The average NLR value in patients with PPP was significantly higher than that in healthy controls (2.30 +/- 1.02 vs 1.69 +/- 0.45, P < 0.001). A comparative analysis of patients with PPP with and without infectious complications showed that there was a statistical difference in the NLR between patients with PPP with and without focal infections, whereas no significant difference was found for metal allergy, smoking, and pustulotic arthro-osteitis. Multivariate analysis indicated that the NLR was significantly associated with focal infections (odds ratio = 18.38, 95% confidence interval 3.86-87.35, P < 0.001). The NLR was also significantly correlated with C-reactive protein levels (P = 0.013, r = 0.2857). Interestingly, after symptom improvement, the NLR significantly decreased from the baseline levels. Furthermore, statistical analysis using the Youden's index revealed that an NLR of 2.28 or higher was associated with the risk of any focal infections in patients with PPP. These results suggest that the NLR has potential applications as a biomarker of the presence of focal infections in patients with PPP.