HYPOKALEMIA AS A HIDDEN CAUSE OF CUSHING DISEASE

Abstract

INTRODUCTION/BACKGROUND
Cushing disease is caused by an adrenocorticotropic hormone (ACTH)-secreting pituitary adenoma, and it comprises 70% of endogenous Cushing syndrome. Cushing disease is rare and is associated with high morbidity and mortality. The diagnosis is often delayed due to its manifestations of variable clinical features. Cortisol also has mineralocorticoid activity, and hypokalemia occurs when severe hypercortisolism occurs.

CASE
A 34-year-old female with a past medical history of type 2 diabetes mellitus, hypertension and polycystic ovarian syndrome. She was admitted for the first time 5 years ago for uncontrolled diabetes mellitus and complained of subacute onset of recurrent bilateral lower limb weakness and excessive weight gain. There was no history of neck trauma, gastrointestinal losses, thyrotoxic symptoms and treatment with corticosteroids. Physical examination revealed classical cushingoid features with truncal obesity, thin limbs, moon face, facial acne, dorsocervical fat pad and purplish abdominal striae. She was hypokalemic with serum potassium of 2.6-2.8 mmol/L and alkalotic with a bicarbonate level of 32 mmol/L. The thyroid function test and serum magnesium were normal. She received both enteral and parenteral potassium supplementation. Cushing syndrome was considered and further evaluation confirmed ACTH-dependent Cushing syndrome with a non-suppressed overnight dexamethasone test with raised serum cortisol, 24-hour urinary cortisol and ACTH. The pituitary MRI showed a microadenoma (8.2 x 9.4 x 8.3 mm). She was started on steroidogenesis inhibitors (ketoconazole) preoperatively. She underwent transsphenoidal surgery (TSS), and histopathology confirmed a pituitary adenoma. However, she still had persistent Cushing disease post-operatively with non-suppressed serum cortisol, poor glycemic control with HbA1c of 11-13% and mild hypokalemia. A repeat pituitary MRI was scheduled, and a repeat TSS is likely warranted.

CONCLUSION
Although hypokalemia is not a determining feature of CD, it can be a significant presentation. Hence, a high index of clinical suspicion of the possible etiologies in evaluating hypokalemia is essential.