Ectopic ACTH is rare and represents about 10% of causes of Cushings syndrome. Associated tumours are neuroendocrine in origin and include small cell lung cancer, carcinoid tumours, and medullary carcinoma of the thyroid. In this report, we describe a rare case of ectopic ACTH due to a primary pulmonary carcinoid tumour.
A 29 years old male was diagnosed with hypertension 18 months prior to presentation. On examination, he had dark striae on his abdomen and axilla, and complained of muscle wasting, myalgia, fatigue, and facial acne. Suspected Cushings syndrome was confirmed biochemically with random cortisol at 980 nmol/L (35.5 mcg/dL) and ACTH at 159 pg/mL (35 pmol/L). Following 8 mg dexamethasone suppression, a 24 hour urine free cortisol of 59 mcg (162 nmol) confirmed the clinical findings. Radiological investigation showed normal adrenal glands and pituitary imaging showed slight enhancement but could not exclude a micro-adenoma. Inferior petrosal sinus sampling (IPSS) for ACTH was performed.
Laboratory findings: Hyperglycaemia on presentation with HbA1c at 9.6%, moderate hypernatremia (151 mmol/L), normal renal function, persistent hypokalaemia <3.6 for two years with normal bicarbonate levels except for two occasions of mild alkalosis (bicarbonate 33 mmol/L). IPSS ACTH levels showed flat response in both petrosal samples (ratios to venous levels <2) and was diagnostic of ectopic ACTH production. Chest CT showed a 2.4 cm upper lobe lesion which was suspected to be an intrapulmonary bronchogenic cyst. An octreotide scan showed the lesion to be Octreotide avid. A right upper lobectomy and mediastinal lymph node dissection was subsequently performed and histology showed a unifocal typical carcinoid tumour measuring 2.1×1.8×1.6 cm, with 2/3 lymph nodes positive for metastatic tumour. Immunohistochemistry was positive for ACTH. On follow up the patient was doing well. His Cushings resolved and he showed sustained weight loss, control of this diabetes improved (HbA1c 6.0%), and his hypertension was controlled with amlopidine (5 mg).