Nonmetastatic Pulmonary Carcinoid Presenting With Carcinoid Syndrome Despite Negative 5-HIAA: A Case Report.

Background: Carcinoid syndrome from pulmonary carcinoids without hepatic metastases is rare and diagnostically challenging when biochemical markers are normal. Case Presentation: A woman in her mid-60 s presented with an incidental right adrenal mass during evaluation for dyspnea and elevated D-dimer. She reported a 20-year history of paroxysmal tachycardia and 5 years of episodic flushing, profuse sweating, exertional dyspnea, and fine tremors triggered by minimal physical activity. Imaging revealed a 3.6 cm lipid-rich adrenal adenoma and an 8 × 10 mm left upper lobe pulmonary nodule. Comprehensive biochemical evaluation was normal: 24 h urinary 5-hydroxyindoleacetic acid 6 mg/d (normal 0-15), chromogranin A 50 ng/mL (normal 0-187), plasma metanephrine 0.12 nmol/L (normal 0.00-0.49), and normetanephrine 0.68 nmol/L (normal 0.00-0.89), excluding pheochromocytoma. Fine needle aspiration of the left pulmonary nodule confirmed a typical carcinoid tumor. Left upper lobe trisegmentectomy revealed low-grade neuroendocrine neoplasm (pT1b pN0) with minimal mitotic activity (<1 per 10 HPF) and no necrosis. Postoperative 68Ga-DOTATATE PET/CT demonstrated a radiotracer-avid suspicious right lower lobe nodule (SUVmax 2.8) without hepatic metastases. Surgery markedly improved carcinoid syndrome symptoms, with residual episodes responding to long-acting octreotide 20-30 mg every 4 weeks. Discussion: This case illustrates that pulmonary carcinoid tumors can present with carcinoid syndrome despite normal biochemical markers and the absence of hepatic metastases. The temporal improvement following resection and response to octreotide established the diagnosis when biochemical testing was uninformative. Conclusion: Clinicians should maintain high suspicion for pulmonary carcinoids in patients with unexplained paroxysmal symptoms, even with negative biochemical testing and absent metastatic disease.