S3852 Unusual Presentation of Colorectal Cancer Presenting Through Paraneoplastic Syndrome

Introduction: Colorectal cancer (CRC) often metastasizes to the liver and lungs. However, neuropsychiatric symptoms, including hallucinations, are rarely the initial presenting features. The case underscores importance of considering metastatic cancer in the differential diagnosis of acute-onset hallucinations, especially in older patients. Case Description/Methods: A 65-year-old man with no significant psychiatric history presented to the emergency department with complaints of new-onset visual and auditory hallucinations. The patient described seeing people who were not present and hearing voices that were not audible to others. There was no known history of cancer or recent changes in medications. He denied history of substance abuse. On examination, the patient appeared anxious but was oriented to time and place. Vital signs were stable, and physical examination was unremarkable. Mental status examination confirmed the presence of visual and auditory hallucinations without delusions or mood disturbances. Laboratory tests were within normal limits. Computed tomography (CT) scan of the chest and abdomen revealed 2 pulmonary nodules measuring 1.5 cm and 2.0 cm, suggestive of metastatic disease, and a thickening of the sigmoid colon. Colonoscopy confirmed a mass in the sigmoid colon, and biopsy results revealed moderately differentiated adenocarcinoma. Brain MRI showed no intracranial lesions. Based on above results, patient was diagnosed with CRC with pulmonary metastases. The hallucinations were attributed to paraneoplastic or metabolic effects related to the underlying malignancy. Discussion: The patient was started on antipsychotic medication to manage hallucinations and was referred to oncology for further management of colorectal cancer. He underwent surgical resection of the primary colorectal tumor followed by chemotherapy targeting metastatic disease. Follow-up after 2 months showed a reduction in the size of pulmonary nodules, and hallucinations gradually resolved with ongoing oncological treatment. This case highlights an atypical presentation of metastatic colorectal cancer manifesting as neuropsychiatric symptoms, specifically hallucinations. While colorectal carcinoma commonly metastasizes to the lungs, brain involvement is rare and was ruled out in this patient. The exact mechanism of hallucinations remains unclear but may involve paraneoplastic effects or metabolic derangements due to cancer progression so comprehensive evaluation in patients presenting with unexplained neuropsychiatric symptoms is needed.