Caught in the act - pancreatic actinomycosis masquerading as malignancy.

A 57-year-old male with a background of chronic pancreatitis presented with acutely worsening abdominal pain and vomiting. He previously had a pancreatic duct stent which had been removed 1 year prior to presentation. Initially suspected to be acute-on-chronic pancreatitis, a computed tomography (CT) scan of the abdomen and pelvis revealed an atrophic pancreas and a new mass in the pancreatic head, raising the suspicion of pancreatic malignancy. An urgent endoscopic ultrasound (EUS)-guided fine needle biopsy of the pancreatic head mass surprisingly revealed the presence of actinomyces colonies on histological evaluation. Prompt initiation of a prolonged antibiotic course led to significant clinical and radiological improvement. This case highlights the rare presentation of pancreatic actinomycosis which can often masquerade as malignancy. Although a gut commensal, actinomyces can elicit pathogenic effects if allowed to enter tissues through a breach in the mucosal lining such as following abdominal surgery or pancreatic duct intervention as observed in this case. Early recognition and appropriate treatment with antibiotics can lead to clinical recovery and complete resolution of the infection.