IgG4-related disease (IgG4-RD) presents a diagnostic challenge due to its varied symptoms, lack of specific tests, and symptom overlap with other conditions.1,2 This underscores the need for interdisciplinary collaboration. Accurate diagnosis often demands input from radiologists and experienced physicians, typically rheumatologists. IgG4-RD usually appears as an enhancing soft tissue mass or diffuse infiltrative process on imaging.3 Rarely can a surgical pathologist make a standalone diagnosis of IgG4-RD. The expertise of a trained radiologist and the insight of an experienced treating physician, often a rheumatologist, are essential in guiding the pathologist to an accurate diagnosis. It is wise to remember that the mere elevation of serum or tissue IgG4 does not equate to IgG4-RD.4

In 2019, the American College of Rheumatology and the European League Against Rheumatism introduced a three-step classification system for IgG4-RD.5These classification criteria consist of a 3-step process. 1) To qualify, a patient must have characteristic symptoms in one of 10 key specified organs ; 2) numerous clinical, serologic, radiologic, and pathologic exclusion criteria must be absent; 3) meet specific clinical, serologic, and pathologic criteria while scoring 20 or higher on additional weighted criteria. Initially designed for research, the system has demonstrated high specificity (98 %) and acceptable sensitivity (82 %) for IgG4-RD and shows promise as a diagnostic framework (Table 1).

IgG4-RD can involve every part of the head and neck (Table 2). Over the past two decades, there has been an effort to link various inflammatory diseases with IgG4-Related Disease (IgG4-RD). Some of these associations have been substantiated, while others remain marginally connected to IgG4-RD (Fig. 1). This review focuses on the contentious aspects of IgG4-related head and neck diseases. Like other articles in this Seminar issue, we also discuss conditions that mimic IgG4-RD. Other comprehensive reviews on this topic are available for further reading, including one by one of the authors.6