IgG4 Related Disease: case report and 6-year follow up of an elusive diagnosis mimicking malignancy

Key Clinical Message: IgG4-related disease is a rare and emerging pathology, characterized by the appearance of pseudotumors.Due to the ability to mimic other pathologies, it is essential to consider it as a differential diagnosis in multisystemic processes.The diagnosis is challenging, requiring a multidisciplinary approach, to minimize the associated morbidity and mortality.Abstract: IgG4-related disease (IgG4-RD) is a rare, emerging, systemic and chronic pathology, characterized by the appearance of pseudotumors resulting from tissue infiltration by IgG4-positive plasmablasts that promote eosinophilic inflammation of the tissue with subsequent fibrosis.We present the case of a male, 45-year-old patient, who consulted his Family Health Unit with complaints of postprandial discomfort in the left hypochondrium with a feeling of fullness, weight loss, chronic fatigue and hyperhidrosis that had lasted for a month.During physical examination, he was pale, and had pain at palpation of the left hypochondrium.Laboratory data showed increased inflammation markers, abdominal ultrasound and CT demonstrated numerous enlarged lymph nodes in the upper quadrants, raising concern for a malignant lymphoproliferative process.Laparoscopic excisional biopsy revealed features of IgG4-related lymphadenopathy and excluded malignant lymphoproliferative disease.The increase in serum IgG4 supported the final diagnosis of IgG4-RD.