Acute and General Medicine Physician, Cairns Hospital.
Recalcitrant Hypokalaemia, Metabolic Alkalosis And Hypertension Heralding A Diagnosis Of Ectopic ACTH (Adrenocorticotrophic Hormone) Syndrome And A Neuroendocrine Tumour
We report a 55-year-old female smoker who presented with complaints of abdominal distension and bilateral leg swelling and weakness of 3 weeks duration.
Significant examination findings were raised blood pressure (170/90mmhg), atrophic skin, telangiectasia over chest and back, intrascapular fat pads, distended abdomen with massive non-tender, nodular liver and ascites.
The blood chemistry showed severe metabolic alkalosis (pH 7.65, bicarbonate 42mmol/l), hypokalaemia (2.0mmol/l), and minimally deranged mixed hepatic function. She had received 140mmol of intravenous potassium chloride and oral potassium tablets over the next 24 hours, however severe hypokalaemia persisted.
Given her clinical findings, a diagnosis of Ectopic ACTH syndrome (EAS) was considered as a differential. Severe hypokalaemia of <3.0 in a patient with Cushing’s syndrome is more often suggestive of an EAS as opposed to a pituitary dependent Cushing’s Disease.
The 8mg overnight dexamethasone suppression test showed non- suppressed cortisol level of 3100nmol/l and a high ACTH level (250ng/l). The plasma aldosterone/renin ratio was normal (<1mU/l)
The Computed tomography scan of the chest and abdomen was suggestive of a primary lung cancer with metastasis to liver, peritoneum and subcutaneous tissues.
The biopsy of a subcutaneous nodule confirmed metastatic small cell neuroendocrine tumour as a cause for the EAS.
She was treated with ketoconazole, spironolactone and potassium supplements with improving biochemistry. She declined any treatment for her metastatic disease given its poor prognosis and was referred for palliative care. The optimal therapy for EAS is surgical resection of tumour, if this is impossible, bilateral adrenalectomy or medical therapy with adrenal enzyme inhibitors can be considered.
Ectopic ACTH syndrome could be the first presenting feature for malignancy as illustrated in this case report. The presence of severe hypokalaemia and metabolic alkalosis should prompt the clinician to investigate endocrine causes such as Conn’s syndrome and Cushing’s syndrome