Case Report: A case of primary IgG4-related skin disease presenting initially with skin papules and abscesses.

BACKGROUND: Immunoglobulin G (IgG) type 4-related disease (IgG4-RD) is a rare, chronic fibroinflammatory condition that can affect multiple organ systems. Cutaneous involvement in IgG4-RD is even rarer. Moreover, the clinical manifestations of primary IgG4-related skin disease (IgG4-RSD) are often atypical, making it easy for clinicians to misdiagnose or overlook the condition, leading to delays in diagnosis and treatment.Case presentation: We report the case of a 36-year-old male who was admitted to the hospital due to recurrent papules and pustules at multiple sites across the body for 8 years. He was misdiagnosed with hidradenitis suppurativa at an outside hospital and received long-term anti-infective therapy and irregular prednisone treatment, but experienced recurrent episodes. This admission was prompted by worsening skin lesions complicated by sepsis. Based on clinical clues including chronic recurrent skin lesions, poor response to anti-infective therapy, and symptom relief with corticosteroids but frequent relapses, we performed targeted serum IgG4 testing and skin biopsy, ultimately confirming the diagnosis of primary IgG4-RSD. After treatment with a standardized regimen of glucocorticoids combined with azathioprine as a steroid-sparing agent, the skin lesions significantly improved. At the 2-month follow-up after discharge, no new skin lesions developed, pre-existing lesions had largely healed, and serum IgG4 levels returned to normal.

CONCLUSION: Primary IgG4-RSD is rare and diagnostically challenging, as it can mimic a wide range of diseases and its pathogenesis remains incompletely understood. A definitive diagnosis requires markedly elevated serum IgG levels, characteristic histopathological findings, and rigorous exclusion of mimicking disorders. Additionally, the condition tends to relapse during treatment. Therefore, enhancing clinicians' understanding of IgG4-RD is crucial.