Ectopic Cushing's syndrome in a patient with DIPNECH and metastatic lung carcinoid

Diffuse idiopathic pulmonary neuroendocrine cell hyperplasia (DIPNECH) is a rare precursor to lung carcinoids. We report a case of ACTH-dependent Cushing's syndrome in a 73-year-old female patient with metastatic lung carcinoid arising on a background of DIPNECH. She presented with lower limb oedema, hypokalaemia, hypertension, and de novo diabetes. Clinical suspicion for hypercortisolism was confirmed by abnormal cortisol tests. A thoracic CT scan showed multiple lung nodules suggestive of DIPNECH and biopsy of one of the nodules identified an ACTH-expressing carcinoid tumour. A PET-Ga-68-DOTATOC revealed pulmonary and multiple tumour lesions in the ganglia, bone and liver with overexpression of somatostatin receptors. A liver biopsy demonstrated involvement by a well-differentiated neuroendocrine neoplasia, consistent with metastasis. Hypercortisolism was managed with octreotide and metyrapone, but the patient succumbed to complications 14 months post-diagnosis. This case suggests DIPNECH's potential to progress to hyperfunctioning, metastatic carcinoids and highlights the necessity for vigilant long-term surveillance and early intervention.