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IgG4-related diseases are new systemic autoimmune diseases discovered in Japan in the 21st century. Inflammation occurs in various organs throughout the body, and is characterized by the formation of hard lumps. Differentiation is important because symptoms similar to those of malignant tumors such as cancer may occur. In 2019, internationally unified diagnostic criteria were established, and recognition is gradually increasing.

IgG4-related diseases are characterized by inflammation in various organs throughout the body, and symptoms such as pain and functional decline. The affected organ varies from patient to patient. If the lacrimal and salivary glands are affected, swelling will appear around the eyes and jaw. When it occurs in organs such as the lungs, kidneys, and pancreas, the function of the organs declines. The average age of onset patients is about 60, and the number of patients in Japan is estimated to be in the tens of thousands. It is also designated as a national intractable disease.

Diagnosis of IgG4-related diseases is based on the "International Criteria for Classification of IgG4-related Diseases" established in 2019 led by Professor John Stone of Harvard University. The criteria divide the diagnosis into three steps:

ステップ1エントリー基準:
出現頻度の高い10個の臓器病変（膵臓、唾液腺、胆管、眼窩、腎臓、肺、大動脈、後腹膜、硬膜、甲状腺）の臨床像、画像所見およびリンパ球と形質細胞浸潤の炎症性の病理所見により本疾患を疑います。

ステップ2 除外基準:
臨床像、血液所見、画像所見、病理所見、既知の疾患（潰瘍性大腸炎、クローン病、橋本病など）の5項目からなる除外基準を確認します。除外が認められない場合、ステップ3に進みます。

ステップ3 包括基準:
本疾患を示唆する、（1）組織所見、（2）組織中のIgG4 陽性形質細胞浸潤、（3）血清IgG4 濃度、（4）涙腺、耳下腺、舌下腺、顎下腺病変、（5）胸部病変、（6）膵臓と胆管病変、（7）腎病変、（8）後腹膜病変の8つの領域の所見がスコア化されます。例えば、血清IgG4値が正常上限から正常の2倍までなら4点、2～5倍までなら6点、5倍を超える値なら11点のスコアになります。8項目のスコア合計点が20点以上の場合には、IgG4関連疾患と診断されます。

Autoimmune pancreatitis, a type of IgG4-related disease, is a disease in which inflammation occurs in the pancreas. It often develops in elderly men, and symptoms such as exacerbation of diabetes, obstructive jaundice, pancreatic enlargement, and narrowing of the pancreatic and bile ducts are observed. You can Autoimmune pancreatitis and pancreatic cancer can be difficult to distinguish because the symptoms are similar. Until now, endoscopic retrograde pancreatography (ERP) has been essential for diagnosis because of the risk of complications of pancreatitis, but magnetic resonance cholangiopancreatography (MRCP) and endoscopic ultrasound With the widespread use of fine-needle aspiration cytology (EUS-FNA), it has become possible to distinguish between the two without performing ERP.

IgG4-related diseases are relatively rare diseases, so there are not many doctors who specialize in this disease. In addition, because it is a disease that spans multiple organs, it is necessary for specialists in each organ to treat it cross-organizationally. Against this background, in April 2023, Tokyo Metropolitan Komagome Hospital established the first center in Japan to specialize in treating IgG4-related diseases (Director: Terumi Kanzawa, Honorary Director of Tokyo Metropolitan Komagome Hospital). At the center, physicians from the departments of gastroenterology, collagen disease, ophthalmology, otolaryngology, nephrology, general medicine, radiology, and pathology work together to provide medical care. In the future, it is thought that other regions will also need a comprehensive medical approach in which doctors from various departments cooperate with each other.