Paraneoplastic Motor Neuron Disease in a Patient With Sigmoid Colon Adenocarcinoma: A Case Report

Paraneoplastic neurological syndromes (PNS) are a rare and diverse group of disorders caused by immune-mediated effects of malignancies. These syndromes are very rare and often present diagnostic and therapeutic challenges. Motor neuron disease as a paraneoplastic condition is particularly uncommon, especially in association with gastrointestinal malignancies like sigmoid colon adenocarcinoma. A 62-year-old male with type 2 diabetes mellitus (T2DM) presented with chronic diarrhea and a three-year history of progressive bilateral limb weakness. Initial symptoms were attributed to diabetic neuropathy, but the rapid progression and severity warranted further investigation. Neurological examination revealed hypotonia, muscle wasting, and absent reflexes in all four limbs. Diagnostic tests, including electromyography (EMG) and nerve conduction studies, confirmed motor sensory axonal neuropathy. A colonoscopy revealed a mass in the sigmoid colon, and a biopsy confirmed adenocarcinoma. The patient was managed with surgical resection of the tumor, adjuvant chemotherapy, and immunomodulatory treatments, resulting in the stabilization of neurological symptoms. This case highlights the importance of considering paraneoplastic syndromes in patients with unexplained neurological symptoms, particularly when a malignancy is suspected or known. Early recognition and a multidisciplinary approach are crucial for improving patient outcomes. Further research is needed to understand the pathophysiological mechanisms and develop sensitive biomarkers for early detection.