Green Nail in a Patient With Psoriasis Receiving Deucravacitinib.

Green nail (GN) is typically caused by Pseudomonas aeruginosa and commonly occurs in patients with nail damage, nail psoriasis, or frequent exposure to moist environments. Deucravacitinib is an oral tyrosine kinase 2 (Tyk2) inhibitor effective for psoriasis treatment. Herein, we report a case of GN in a 72-year-old man following four months of treatment with deucravacitinib. Given the absence of pre-existing signs indicative of nail psoriasis prior to the initiation of deucravacitinib, deucravacitinib might have contributed to the development of GN. To the best of our knowledge, no previous cases of GN associated with deucravacitinib or studies discussing a potential link between the two have been reported. Interleukin (IL)-10 plays a crucial role in regulating T-cell immune responses specific to P. aeruginosa. Tyk2 mediates IL-10 signaling and promotes IL-10 activation. In this case, the inhibition of IL-10 function via Tyk2 suppression due to deucravacitinib might contribute to the development of GN.