A Study of KHK4827 in Subjects With Palmoplantar Pustulosis

Inclusion Criteria: * Subject has had a diagnosis of palmoplantar pustulosis for at least 24 weeks as of the time of informed consent. * Subject has a PPPASI total score ≥12 and a PPPASI severity score of pustules/vesicles on the palms or soles ≥2 both at the pre-examination and enrollment examination; * Subject inadequately responded to any one or combination of the following therapies before informed consent: Topical corticosteroids, Topical vitamin D3, Phototherapy, Etretinate Exclusion Criteria: * Subject has a diagnosis of plaque psoriasis, pustular psoriasis, drug-induced palmoplantar pustulosis, or pompholyx; * Subject has an improvement in PPPASI total score of ≥4 points during the screening period; * Subject has a history or evidence of psychiatric disorder or alcohol/drug abuse that, in the opinion of the investigator or subinvestigator, may compromise the safety of the subject because of participation in the study or may interfere with assessments and procedures in the study or study completion; * Subject has a past or current history of suicidal ideation (severity of 4 or 5) or any suicidal behavior at enrollment, as assessed by the Columbia-Suicide Severity Rating Scale (C-SSRS); * Subject has severe depression with a PHQ-8 total score of ≥15 at enrollment