Diagnostic dilemma of IgG4-related primary localized cervical lymphadenopathy associated with aberrant IL-6 expression level

BACKGROUND: Immunoglobulin G4-related disease (IgG4-RD) is a recently recognized inflammatory condition with single- or multi-organ involvement. The disease is characterized by tumefactive lesions with dense IgG4 plasmacytic infiltration (an elevated IgG4(+)/IgG(+) cell ratio of > 40 %), storiform fibrosis, and obliterative phlebitis, with or without elevated serum IgG4 levels. The diagnostic criteria for IgG4-RD, proposed in 2011, were quite comprehensive and practical; however, it is important to remember that other diseases, such as hyper-interleukin (IL)-6 syndromes, may have common histopathological findings. Therefore, the histopathology of suspected IgG4-RD is occasionally not diagnostic. Here, we report a case of IgG4-related primary localized cervical lymphadenopathy without any other organ involvement. To our knowledge, there have been no previous reports of this. Additionally, the disease was associated with a 20-fold increase in IL-6 levels compared to that of the normal range. CASE PRESENTATION: We report the case of a 52-year-old Japanese man who presented with a painless, somewhat diffuse swelling in the left submandibular region. Although the case fulfilled diagnostic criteria for IgG4-RD, the diagnosis was not straightforward due to abnormally high levels of serum IL-6. After systematic evaluation of the patient, a final diagnosis of IgG4-RD was established. Since then, a specialist in connective tissue disorders has evaluated the patient on a regular basis. Two years after his initial visit, no disease progress or systemic involvement has been noted. CONCLUSION: We present a case of an IgG4-related primary localized cervical lymphadenopathy mimicking hyper-IL-6 syndrome. This case can serve as an excellent reminder that the definitive diagnosis of IgG4-RD should be established using a systematic approach, in particular when it appears as an atypical manifestation.