yemenjmedYemen Journal of MedicinecoVolume 5 Issue 2MultidisciplinaryEnglishMay-August 2026NNY20260728ArticleSmall Cell Lung Carcinoma Presenting With Paraneoplastic Diarrhoea Mimicking Carcinoid Syndrome Clinically: A Case ReportEnglishY426430Jen SzeOng1EnglishNRobin Sia WaiJen2EnglishYAlyssia DeGrandi3EnglishYJaideepVazirani4EnglishY10.63475/yjm.v5i2.0374Small cell lung carcinoma (SCLC) is an aggressive pulmonary neuroendocrine malignancy that rarely presents with carcinoid-like manifestations. We report the case of a woman in her 70s who presented with an 8-week history of profuse watery diarrhoea, hypotension, and acute kidney injury. Serum chromogranin A was markedly elevated, and computed tomography demonstrated a right hilar mass with bilateral pulmonary nodules, raising suspicion for a functional pulmonary carcinoid tumour. However, the 24-hour urinary 5-hydroxyindoleacetic acid level was normal, arguing against classical carcinoid syndrome. DOTA-TATE positron emission tomography showed mild to moderate uptake in the hilar lesion but no significant uptake in the pulmonary nodules. Bronchial washing cytology with immunohistochemistry established the diagnosis of SCLC, demonstrating positivity for CD56, synaptophysin, and thyroid transcription factor-1, with a Ki- 67 proliferation index approaching 100%. The patient was treated with carboplatin, etoposide, atezolizumab, and supportive care, resulting in recovery from acute kidney injury. This case highlights that SCLC may present with chronic diarrhoea mimicking carcinoid syndrome and underscores the limitations of biochemical markers and functional imaging. Histopathological examination remains essential for establishing the correct diagnosis and guiding appropriate management.Englishcell lung carcinoma, lung neoplasms, neuroendocrine tumours, paraneoplasticsyndromes, diarrhoea, carcinoid syndromehttps://www.yemenjmed.com/admin/abstract?id=435References1619