IgG4-Related Disease Manifested as Cutaneous Plasmacytosis: A Case Report

BACKGROUND: IgG4-related disease (IgG4-RD) is a rare fibroinflammatory disease that has a high tendency to misdiagnosis in clinics. CASE PRESENTATION: A 48-year-old man developed a rash with progressive itching 3 years ago after hormone therapy for an ocular “inflammatory pseudotumor”. The disease condition of this patient involved multiple organs which involved the skin. The patient was misdiagnosed with other diseases during the period of hospitalization, leading to poor therapeutic effects and repeated skin lesions. The dermatopathological report indicated plasma cell proliferative disorder, with IgG4/IgG exceeding 40% and abnormally elevated serum IgG4 levels. After the patient was diagnosed with IgG4-RD, a series of treatments improved skin lesions, relieved other symptoms, and decreased serum IgG4 levels. CONCLUSION: IgG4-RD is a highly misdiagnosed disease that deserves the attention of physicians. The patient we reported could be considered a representative case of IgG4-RD that presents with skin lesions. For patients with suspected IgG4-RD, serum IgG4 testing should be performed, and further imaging, serological tests, and pathology examinations are needed to exclude malignancy, infection, and autoimmune diseases.