Cushing’s in Woman With Pituitary Tumor Tied to Low Blood Potassium

Margarida Maia, PhD avatar

by Margarida Maia, PhD |

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Cushing’s disease may occur secondary to a large pituitary tumor and, in rare cases, cause potassium levels in the blood to be persistently low, a recent case report highlighted.

According to its authors, this case serves as a reminder that doctors should suspect Cushing’s when potassium levels remain low despite treatment.

The case study, “Refractory hypokalaemia and hypertension with metabolic alkalosis: an acute presentation of Cushing’s disease secondary to a pituitary macroadenoma,” was published in the journal BMJ Case Reports.

While Cushing’s syndrome is marked by high levels of the stress hormone cortisol, Cushing’s disease, a form of Cushing’s syndrome, is caused by the brain’s pituitary gland making too much adrenocorticotropic hormone (ACTH), a hormone that controls the production of cortisol by the adrenal glands. This is often due to the presence of a pituitary adenoma (a benign tumor), which is usually small — measuring 10 millimeters in diameter or less.

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Aggressive Form of Cushing’s Disease Masks as Ectopic Cushing’s Syndrome

A team of researchers in the U.K. described treating a 68-year-old woman with Cushing’s disease who had a large pituitary adenoma that invaded nearby tissues.

She also had unusually low blood potassium levels, or hypokalemia — a condition more commonly seen in people with ectopic Cushing’s syndrome, another form caused by tumors found outside the brain’s pituitary gland that release ACTH.

The woman came to a hospital for inflammation in her right arm that was not responding to oral antibiotics. An ultrasound — an imaging test that uses sound waves to image tissues inside the body — confirmed the presence of excessive amounts of fluid in the arm, while blood tests came back positive for the bacteria Staphylococcus aureus. Those bacteria were found to be sensitive to the antibiotic flucloxacillin, and she started on intravenous treatment.

A physical exam identified an excessive fat accumulation in her abdominal area and stretch marks. Blood tests also revealed she had hypokalemia, high levels of inflammatory markers, and metabolic alkalosis — a condition that occurs when the blood becomes overly alkaline.

Hemoglobin A1c — a blood sugar indicator — was also high, suggesting poor blood sugar control, as was her blood pressure. The woman also started on potassium to treat her hypokalemia, and metformin plus insulin to manage her blood sugar.

“These clinical findings and refractory hypokalaemic hypertension [high blood pressure] with metabolic alkalosis raised a suspicion of Cushing’s syndrome,” the researchers wrote.

Indeed, cortisol levels in the urine and blood were higher than normal, as were ACTH levels in the blood. A pituitary MRI scan revealed the presence of a large adenoma, measuring 12–16 millimeters in diameter, as the source of excessive ACTH production.

Metyrapone, a cortisol-lowering medication marketed under the brand name Metopirone, followed by tumor debulking — a surgical technique to remove of as much of a tumor as possible — via transsphenoidal adenomectomy reversed the hypokalemia and metabolic alkalosis. It also helped to lower her blood sugar levels and blood pressure.

“After the operation and in the follow up period she felt very well in herself and noticed a clear improvement in her health,” the researchers wrote.

“This case illustrates the importance of a stepwise approach in dissecting the cause of refractory hypokalaemia in clinical practice as the underlying cause may be rare, and if missed, can have catastrophic clinical consequences for the patient. [Cushing’s syndrome] is a rare cause of hypokalaemia but should be screened for in cases of refractory [unresponsive] hypokalaemia,” they concluded.