Endocrine Abstracts (2002) 3 P255

Intermittent hyponatraemia due to isolated ACTH deficiency

R Ajjan, E Scott, A Ismail, P Walker & DK Nagi

Department of Diabetes and Endocrinology, Pinderfields General Hospital, Wakefield, UK.

A 61 year old woman presented with a six months history of nausea, vomiting and lethargy. She is a non-smoker and drinks little alcohol. She was on 100mcg of Thyroxine following partial thyroidectomy. Physical examination was unremarkable apart from postural hypotension (BP 140/80mmHg laying, 105/75mmHg standing). Blood tests showed plasma sodium of 121mmol/L with normal potassium, urea, creatinine, FBC, random glucose and TFTs. A short synacthen test (1mcg) was normal with a peak cortisol of 605nmol/L. She was treated with two litres of intravenous normal saline and her plasma sodium normalised and was subsequently discahrged. Her plasma sodium 6 weeks after her discharge was 139mmol/L. Six months later, she presented again with 4-6 similar episodes, each lasting 2-7 days with spotaneous recovery and a documented plasma sodium of 121mmol/L. She was readmitted acutely with similar symptoms and severe hyponatraemia. A random cortisol was low at 94 nmol/L. A short synacthen test (250mcg) showed a suboptimal response with peak a cortisol of 408nmol/L. The patient was started on hydrocortisone replacement. Plasma ACTH was 11ng/L and adrenal antibodies were negative. Further tests showed a plasma FSH of 69IU/L, LH 18IU/L, prolactin 329IU/L, undetectable random growth hormone and an IGF-I of 24.8nmol/L. A long synacthen test was normal with a peak cortisol of 798nmol/L. She failed to show any ACTH response to CRH test (ACTH <10-12ng\/L). A CT scan of her pituitary was normal and a MRI is awaited.

We describe a case of isolated idiopathic ACTH deficiency presenting with intermittent hyponatraemia over a 12 months period with spontaneous recovery of each attack. The patient has had no further episodes over the past 6 months, following hydrocortisone treatment.

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