A rare cause of hypokalaemia and metabolic alkalosis.

A 72-year-old man with a medical history of diabetes mellitus Type II, paroxysmal atrial fibrillation and heart failure was hospitalized after a syncope. Pitting oedema in both legs were the only abnormal finding on physical examination, in particular the patient had no cushinoid features. The blood pressure was slightly elevated at 160/90 mmHg. Regular medications consisted of furosemid 100 mg, digoxin 0.125 mg, warfarin, enalapril 10 mg, metoprolol 50 mg, aldactone 25 mg and insulin. He was not overweight.

Routine blood tests were normal, except for potassium 1.7 mmol/L, creatinine 122 μmol/L and albumin 29 g/L. Blood gas test showed a pronounced metabolic alkalosis, with pH 7.54, bicarbonate 41 mmol/L, base excess 17 mmol/L, PCO2 5.79 kPa and PO2 12.3 kPa. Urine levels of sodium and potassium on admission in a spot urine were 86 and 41 mmol/L, respectively. Both at 8 am and at 8 pm, cortisol levels were elevated. Dexamethasone suppression tests showed no ability of suppression. Despite treatment with intravenous (i.v.) and oral potassium, i.v. MgSO4 and an incremental increase in the aldactone dosage from 25 to 600 mg daily, he remained hypokalaemic with metabolic alkalosis.

Magnetic resonance imaging (Figure 1), revealed an expansive process in the sinonasal cavity, exerting compression into the medial walls in both orbita. A biopsy taken from the tumour in the sinonasal cavity (Figure 2) showed neuroendocrine tumour, probably a neuroblastoma, with a strongly positive reaction for neuroendocrine markers, later also shown to stain positively for adrenocorticotropic hormone (ACTH).

Fig. 1.

MRI caput.

Fig. 2.

Tumour histology.

Chest X-ray did not show any lesions, and the cancer marker neuron specific enolase was negative, so we did not find it likely that the tumour was metastatic originating from primary lung cancer.

The patient’s condition, including cognitive status, was rapidly deteriorating. Five weeks after hospitalization, the tumour was surgically removed. Histology showed infiltration to dura, no signs of metastasis. Three months after admission he died, assumed cause of death being sepsis, most probably due to pneumonia. The relatives refused autopsy.

The location of the ACTH-producing tumour in the paranasal sinuses is uncommon and often not recognized (1). Ectopic ACTH production is usually suggested by cushinoid appearance, which this patient did not have, marked hypokalaemia, increased 24-h urinary-free cortisol excretion and elevated serum ACTH (2).