ACTH-secreting bronchial carcinoid: a diagnostic and therapeutic challenge

We describe a case of Cushing's syndrome due to ectopic ACTH secretion, where the only potential source on conventional imaging was a tiny benign-appearing lung nodule, which failed to take up radiolabelled octreotide.

To determine whether the patient might respond to therapeutic administration of octreotide, a test dose was given.

Compared to ACTH and cortisol levels on a control day, the levels following the test dose of octreotide were lower. Subsequent therapeutic administration of subcutaneous octreotide normalised urine free cortisol, with symptomatic improvement, pending evaluation for surgery. Eventual resection of the lung nodule resulted in cure of hypercortisolism. Histological examination of the resected specimen confirmed bronchial carcinoid staining positive for ACTH.

This is one of the few cases described where ectopic ACTH secretion secondary to bronchial carcinoid responded to somatostatin analogue therapy. The case was also unusual in that the tumour responded despite not taking up radiolabelled octreotide.