Endocrine Abstracts

A 70-year-old female presented with general lethargy and a two day history of painful muscle twitching and paraesthesia in her right hand. No other symptoms were reported. Past medical history included hypertension, hypothyroidism and she had recently been diagnosed with Type 2 diabetes. Examination was unremarkable.

The overall biochemical picture was that of a hypokalaemic alkalosis with hypocalcaemia and hyperglycaemia: Na⁺140 mmol/l, K⁺2.9 mmol/l, urea 8.9 mmol/l, creatinine 51 μmol/l, corrected Ca²⁺2.05 mmol/l, albumin 31 g/l, phosphate 0.64 mmol/l, Mg²⁺0.89 mmol/l, ALT 61 (<40) IU/l, ALP 252 IU/l, random glucose 21.4 mmol/l, HbAlc 66 mmol/mol, PTH 53.2 (1.5–7.6) pmol/l and 2400 h urinary calcium 3.97 mmol/d (2.5–7.50). CXR revealed a mass at the superior aspect of the right hilum. Venous gas showed a metabolic alkalosis (pH 7.51, HCO₃ 32.4).

A subsequent CT confirmed a right upper lobe lung tumour with mediastinal nodes and liver metastases (T3, N2, M1b). During her admission serum calcium spontaneously dropped to 1.67 mmol/l and potassium levels to 2.0 mmol/l. Calcium and potassium levels were normalised with aggressive electrolyte replacement. The association of a primary lung tumour, new-onset diabetes, hypertension and hypokalaemia suggested the possibility of ectopic ACTH. A random cortisol was >4140 nmol/l, and a follow-up 1mg overnight dexamethasone test showed failure of suppression of cortisol >4140 nmol/l with plasma ACTH 1197 (<47) ng/l.

A diagnosis of Cushing’s syndrome secondary to ectopic ACTH production was made. Liver biopsy established a diagnosis of metastatic poorly differentiated neuroendocrine carcinoma of small cell type from a lung primary. Unfortunately the patient’s condition deteriorated and she was offered palliative care.

This case describes atypical presentation of ectopic Cushing’s syndrome complicated by profound hypocalaemia.