A 60-year-old male presents with frequent episodes of flushing and diarrhea. Blood tests show elevated serotonin levels and increased 24-hour urinary 5-HIAA. What are the potential diagnoses and next steps?
These symptoms and lab findings are suggestive of a carcinoid syndrome, a paraneoplastic syndrome associated with neuroendocrine tumors (NETs), typically found in the gastrointestinal tract or lungs. The next steps would include imaging studies to locate the primary tumor (e.g., CT scan, MRI, or nuclear imaging like Octreotide scan or Gallium-68 DOTATATE PET/CT), followed by a biopsy for histologic confirmation. Treatment usually involves surgery, somatostatin analogs, and potentially targeted therapies or systemic chemotherapy for advanced disease.