Hyponatraemia secondary to the deficiency of adrenocorticotropic hormone

Ala Haqiqi1, Karim Meeran1.

Department of Endocrinology and Diabetes, Charing Cross Hospital, Imperial College Healthcare NHS Trust, London, UK.

Introduction: 10% of intracranial tumours are pituitary, and ~30% of the pituitary adenomas are non-functioning. The symptoms of pituitary adenomas could be due to mass effect causing alteration in pituitary hormone production. Pituitary tumours are the most common cause of hypopituitarism. Hyponatraemia is often encountered in clinical practice, and it can be secondary to many conditions including syndrome of inappropriate anti-diuretic hormone secretion (SIADH), and hyponatraemia associated with low cortisol level.

It is thought that a possible mechanism of apparent SIADH secondary to adrenocorticotropic hormone (ACTH) deficiency is likely related to the effect of cortisol in suppressing vasopressin action by allowing free water clearance.

Here we report a case of hyponatraemia associated with ACTH deficiency on the background of non-functioning pituitary adenoma in an elderly patient.

Report of the Case: A 78-year-old lady presented to the emergency department with a 2-month history of fatigue, nausea, weight loss, and abdominal pain (with previously normal blood electrolytes 7 days prior to her admission). She was subsequently admitted and noted to have hyponatraemia with sodium of 122. Initially based on the findings of paired osmolality and hyponatraemia, the possibility of SIADH was considered. 

Biochemistry results were as follows:

Blood Osmolality 246 mOsm/kg

Urine Osmolality 544  mOsm/kg

Urine Sodium level 99 mmol/L

Urine Potassium level 51.7 mmol/L

Cortisol level was 36 nmol/L

Prior to this admission, the patient was worked up for gastrointestinal malignancy in the outpatient setting. The investigations showed no evidence of malignancy, and the patient was subsequently discharged from gastroenterology care. However, the patient’s symptoms had not resolved.

This patient had a background of a non-functioning pituitary macro-adenoma with haemorrhagic change which was diagnosed 10 years prior to this presentation. Previous follow-up scans demonstrated stable appearance initially and reduction in size over serial imaging, with normal pituitary function on dynamic testing in 2016. The patient was also clinically asymptomatic. Hydrocortisone replacement therapy was therefore stopped. It was however decided to maintain her thyroxine treatment.

Around the time of admission, a 3-year interval magnetic resonance imaging (MRI) scan demonstrated significant increase in the size of the residual adenoma with a mixed solid but predominantly cystic composition.  The visual fields were not affected on testing.

Based on the past medical history, clinical, radiological and biochemical findings, ACTH deficiency was postulated as a cause for this presentation. The patient was commenced on prednisolone 4mg once daily as replacement with immediate clinical and biochemical improvement within only 2 days:

Blood Osmolality 285 mOsm/kg

Urine Osmolality 101 mOsm/kg (so much improved free water clearance)

Urine Sodium level <20 mmol/L

Urine Potassium level 2.8 mmol/L

Clinical and imaging follow up were recommended by the pituitary multidisciplinary team (MDT). During follow up consultations, the patient has been feeling much better on prednisolone and levothyroxine replacement.

This case highlights the importance of considering ACTH deficiency as one of the causes of a presentation mimicking SIADH.

Learning Points:

·       Always consider pituitary adenomas –hypopituitarism and low cortisol level as differential diagnosis with a biochemical picture of SIADH. It is essential to always exclude endocrine causes in SIADH presentation.


·       Bear in mind that although the pituitary tumour appeared stable on serial imaging, there is always a risk of recurrence.



1.Gsponer J, De Tribolet N, Déruaz JP, Janzer R, Uské A, et al. Diagnosis, treatment, and outcome of pituitary tumors and other abnormal intrasellar masses. Retrospective analysis of 353 patients. Medicine (Baltimore). 1999 Jul;78(4):236-69.

2. Snyder P. Clinical manifestations and diagnosis of gonadotroph and other clinically nonfunctioning pituitary adenomas. UptoDate. Last updated: May 18, 2018.

3. Oelkers W. Hyponatremia and inappropriate secretion of vasopressin (antidiuretic hormone) in patients with hypopituitarism. N Engl J Med. 1989;321(8):492. 

4. Asano T, Aoki A, Sasaki M, Ikoma A, Kakei M, et al. Hyponatremia is the valuable manifestation for initiating diagnosis of hypopituitarism in elderly. Endocrine Journal.  2012, 59 (11):1015-1020.


2008 MRI Scan:



2008 MRI Scan:












Follow-Up MRI Scans:











MRI August 2018: