Atypical presentation of Cushing’s disease with weight loss and hypokalemia

Background

Pituitary corticotropin (ACTH)-induced Cushing’s disease (CD) accounts for approximately 70% of patients presenting with Cushing’s syndrome (1). ACTH-producing pituitary adenomas are typically microadenomas and, in over a third of CD patients, there is no demonstrable lesion on MRI (2). Clinical and biochemical diagnosis of CD may be challenging, as patients can present with varied symptoms that overlap with other comorbidities. Progressive weight gain associated with central adiposity is a common manifestation of CD occurring during the early stage of the disease. While nonspecific features such as hypertension, diabetes, cardiac hypertrophy, arterial and venous thrombosis, electrolyte abnormalities, and psychiatric disturbances also occur frequently, the more discriminatory signs of hypercortisolemia include proximal myopathy, facial plethora, easy bruising, and wide striae (2). Weight loss with associated hypokalemia typically suggests an underlying ectopic ACTH production. Here we report an unusual case of pituitary ACTH-induced CD who presented with significant hypokalemia and marked weight loss which resolved with medical control of CD.

Case presentation

A 75-year-old female with a history of type 2 diabetes, hypertension, osteoporosis, and coronary artery disease presented to the emergency department (ED) with profound proximal muscle weakness associated with a serum potassium of 2.4 mmol/L (normal = 3.6–5.2 mmol/L). She also reported a weight loss of 90 lbs over the previous 2 years. In addition, she had uncontrolled hypertension despite taking three anti-hypertensive agents and worsening glycemic control requiring increasing anti-hyperglycemic therapy; her hemoglobin A1c at presentation was 9.3%.

Investigation

During hospitalization, she underwent further investigation for hypokalaemia and resistant hypertension, which showed an elevated 24-h urine free cortisol (24-h UFC) of 1904.4 nmol/d (upper limit of normal: 485.4 nmol/d) and consequently was referred to Endocrinology for further assessment. Repeat outpatient-based investigations after discharge from the hospital confirmed an elevated 24-h UFC of 1578.4 nmol/d, elevated AM serum cortisol of 1749.2 nmol/L (normal: 80–477.3 nmol/L), non-suppressed serum cortisol of 1238.8 nmol/L (normal response: < 50 nmol/L) after a 48-h low dose dexamethasone suppression test, and an elevated serum ACTH at 8.2 pmol/L (normal: 0.5–2.2 pmol/L). MRI of the sella as well as gallium DOTATATE PET-CT did not show any demonstrable lesion (Figs 1A, B and 2A, B). Subsequently, she underwent bilateral inferior petrosal sinus sampling (BIPSS) using 100 µg ovine CRH, which showed a post-CRH central to peripheral ACTH ratio of 3, lateralizing to the right with a ratio of 2.1. Based on these findings, a diagnosis of MRI-negative CD was made.

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(A and B) MRI Sella post-GAD coronal and sagittal sections showing no pituitary lesion.

Citation: Endocrinology, Diabetes & Metabolism Case Reports 2024, 3; 10.1530/EDM-24-0011

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(A and B) Ga68 DOTATATE scan. PET-CT showing non-specific uptake through the distal esophagus and proximal stomach, but otherwise within normal physiological limits.

Citation: Endocrinology, Diabetes & Metabolism Case Reports 2024, 3; 10.1530/EDM-24-0011

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Treatment

While awaiting surgical opinion, the patient was started on Ketoconazole 200 mg po TID. She was unable to tolerate a larger dose; therefore, cabergoline 1 mg twice a week was added. The options of trans-sphenoidal pituitary surgery and bilateral adrenalectomy were discussed with the patient, which she declined, and decided to continue with medical therapy.

Outcome and follow-up

Medical therapy was adjusted over the next several weeks until 24-h UFC normalized and remained normal during 24 months of follow-up with the most recent being 85 nmol/d. With biochemical remission of CD, her blood pressure normalized, and she required a reduction in the dose of anti-hypertensive and anti-hyperglycaemic therapy. Her serum potassium levels also normalized. She initially regained 15 lbs but called the clinic when, despite taking medical therapy, she once again began losing weight and her serum potassium dropped to 2.7 mmol/L. Repeat serum AM cortisol was significantly elevated at 935.3 nmol/L, as was 24h UFC at 1457.3 nmol/d. Further inquiry revealed that she had been prescribed omeprazole therapy by her family physician for symptoms of reflux. Omeprazole was discontinued due to its potential effect on decreasing the efficacy of ketoconazole therapy, and her cortisol and potassium levels rapidly normalized. Since then, she has regained 50 lbs, being almost back to her baseline weight, and her mobility and strength have improved from being initially bed-bound to now mobilizing independently using a walker. Pre and post therapy values are summarized in Table 1.

Discussion

Here we report an unusual case of CD presenting with features that were initially highly suggestive of ectopic ACTH production with weight loss rather than the usual weight gain. All of the initial symptoms resolved following biochemical control of hypercortisolemia. In our review of the literature, CD associated with weight loss has previously only been reported in association with severe depression, psychosis, eating disorders, or malignancy (3, 4). For instance, a case of familial CD was reported in a child who also had an intercurrent eating disorder (anorexia), which led to weight loss despite CD (3). Weight loss due to ectopic ACTH-induced CD has also been previously reported, where weight loss was thought to be due to the underlying malignancy (4). However, our patient had well-documented pituitary ACTH-induced CD.

Chronic hypercortisolemia is associated with increased abdominal adiposity that is thought to be caused by the downregulation of adenosine monophosphate-activated protein kinase (AMPK), which is responsible for regulating lipid metabolism (5). Furthermore, glucocorticoids also induce a direct orexigenic effect, which leads to weight gain (6). Weight loss in association with hypercortisolemia, on the contrary, can be a presenting feature of ectopic ACTH-producing tumors such as small cell lung cancer. While the underlying mechanism of weight loss is not fully understood, it is thought to be partly due to cAMP/Protein kinase A (PKA) pathway activation, with an increase in PKA activity resulting in altered downstream regulation of cAMP-related lipogenic and lipolytic proteins (6). In addition, high ACTH secretion and the malignant characteristics of the neoplastic process are also thought to play roles in weight loss (7). Our patient had no evidence of ectopic ACTH production.

A previous study (8) comparing the clinical features of CD in older vs younger patients reported that weight gain was more common in younger individuals, whereas older patients typically presented with catabolic changes, likely due to age-related variability in tissue sensitivity to glucocorticoid receptors and intracellular cortisol signaling. The overall rates of central adiposity were 71.1% in older patients compared with 80.0% in younger patients (8).

Another unusual feature was hypokalemia, which is generally associated with ectopic ACTH production. However, up to 10% of CD patients present with low potassium. Hypokalemia is caused by the mineralocorticoid effect of excess cortisol. Supraphysiologic production of cortisol tends to saturate 11β-hydroxysteroid dehydrogenase type II (11β-HSD2) activity in the renal tubule, which is primarily responsible for converting active cortisol into inactive cortisone. This could lead to excess binding of cortisol to mineralocorticoid receptors, resulting in an increase in potassium excretion and thus hypokalemia. While some studies have suggested that ACTH can also lead to lowering 11β-HSD2 activity causing hypokalemia, others have not found any such correlation (9, 10). In our patient, serum potassium normalized after she achieved eucortisolemia with medical therapy.

Declaration of interest

The authors declare that there is no conflict of interest that could be perceived as prejudicing the impartiality of the study reported.

Funding

This research did not receive any specific grant from any funding agency in the public, commercial, or not-for-profit sector.

Patient consent

Written informed consent for publication of their clinical details and/or clinical images was obtained from the patient/parent/guardian/relative of the patient.

Author contribution statement

All authors reviewed the results and approved the final version of the manuscript.

Acknowledgements

We thank Dr Brian Moses (Yarmouth Regional Hospital, NS, Canada) and Dr Scott Lee (Valley Regional Hospital, NS, Canada) for their contributions in managing the patient.