Annals of Clinical Biochemistry > Volume 45, Number 5 > Pp. 520-523

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Case Reports

Intermittent severe, symptomatic hyponatraemia due to the nephrogenic syndrome of inappropriate antidiuresis

Steven Soule¹, Chris Florkowski², Howard Potter², David Pattison³, Martin Swan⁴, Penny Hunt¹ and Peter George²

¹ Department of Endocrinology; ² Canterbury Health Laboratories, University of Otago Christchurch School of Medicine and Christchurch Hospital, Private Bag 4710, Christchurch, New Zealand; ³ Aspen Medical, RAMSI Medical Facility, PO Box 1597, Honiara, Solomon Islands; ⁴ Medical Treatment Centre, Burnham Military Camp, Private Bag 4720, Burnham, New Zealand

Corresponding author: Dr Steven Soule. Email: steven.soule{at}cdhb.govt.nz

A 20-year-old fit male soldier presented on two separate occasions 16 months apart with severe, symptomatic hyponatraemia and a clinical and biochemical picture consistent with the syndrome of inappropriate secretion of antidiuretic hormone (SIADH). In the intervening period, repeated plasma sodium values were in the reference range. Intensive investigation failed to reveal a cause for SIADH that was initially considered idiopathic. The description of a family comprising several adults with intermittent or water load induced-hyponatraemia associated with an activating mutation in the arginine vasopressin (AVP) receptor type 2 (AVPR2) raised the question of whether our patient could have a similar ‘nephrogenic syndrome of inappropriate antidiuresis’. Mutational screening of AVPR2 in our patient revealed a single missense mutation (R137C) in the second intracellular loop, which has been associated with constitutive activation of the AVPR2. In conclusion, adults with intermittent, severe hyponatraemia may have a constitutively activating mutation in the AVPR2 with resultant nephrogenic syndrome of inappropriate antidiuresis. Patients with idiopathic SIADH, particularly those with unmeasurable circulating AVP concentrations, should be considered for mutational screening of AVPR2.

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