Unusual paraneoplastic syndromes in pancreatic cancer: a case report of Lambert-Eaton myasthenic syndrome (LEMS) associated with intraductal papillary mucinous cancer of the pancreas

BACKGROUND: Lambert-Eaton myasthenic syndrome (LEMS) is an autoimmune disorder of the neuromuscular junction. It can occur as a paraneoplastic disorder associated with various types of carcinomas, usually small cell lung cancer or as an autoimmune disease. LEMS can be misdiagnosed as myasthenia gravis or as an oncological sequela, causing delays in diagnosis. We present a rare case of a male adult with confirmed LEMS occurring with pancreatic carcinoma. CASE DESCRIPTION: A 66-year-old man presented with a newly diagnosed pancreatic tumor. He had been experiencing weakness and fatigue in his lower extremities since the summer of 2020. Over time, the weakness progressed to include his proximal upper extremity muscles. Dysphonia, dysarthria, decreased appetite and significant weight loss were also observed. A computed tomography (CT) scan revealed a 3 cm locally resectable cystic tumor in the pancreatic head. Blood tests showed elevated carbohydrate antigen 19-9 (CA19-9) and carcinoembryonic antigen (CEA) levels. A Whipple procedure was performed, which revealed a poorly differentiated pancreatic adenocarcinoma inside an intraductal pancreatic mucinous neoplasm. Postoperatively, the patient was admitted to the intensive care unit (ICU) because he had no spontaneous breathing and manifested areflexia signs. A train of four (TOF) monitoring of peripheral nerve stimulation was performed and pyridostigmine therapy was initiated, leading to an improvement in symptoms allowing the extubation and transfer to the peripheral ward. Further diagnostic tests revealed a LEMS and an intravenous therapy with cumulative 100 g immunoglobulin (Ig) G was initiated. Upon discharge, 10 days after starting LEMS treatment, the patient showed subjective and objective improvement in strength. CONCLUSIONS: Paraneoplastic syndromes are more common than expected, but rare in pancreatic adenocarcinoma. They can appear before abdominal symptoms, facilitating early diagnosis. Successful treatment of cancer may eliminate paraneoplastic symptoms. LEMS may reveal pancreatic cancer. Early recognition of paraneoplastic syndromes is important for pancreatic cancer management. Further investigation is needed to evaluate the diagnostic approach for LEMS in all patients with pancreatic cancer.