Introduction: Hyponatraemia presents a diagnostic challenge in acute medicine. Suggestive symptoms may be present or it can be an incidental finding. Whether it is acute or chronic, associated with excessive, normal or reduced intravascular volume all help determine cause and correct management.
Case report: A six-year-old boy with a good neurological outcome from extreme hyponatraemia (initial sodium 96 mmol/l) caused by autoimmune hypoadrenalism. He presented with one week of reduced appetite, lethargy, vomiting, and one episode of diarrhoea. He was described as being slightly unsteady on his feet.
Examination: Alert, although intermittently confused, with dry mucous membranes and sunken eyes. Clinically 10% dehydrated, serum sodium was 96 mmol/l with normal serum potassium and renal function.
Cortisol (283 nmol/l) at presentation was considered suspiciously suboptimal for degree of illness. He was initially treated with 3% saline i.v., and by day 3 serum sodium increased to 128 mmol/l. Day 4 he developed slurred speech and ataxia, although MRI brain showed no evidence of pontine myelinosis. Symptoms resolved over one week. Interestingly, a further random serum cortisol on day 8 was reassuringly normal (607 nmol/l), although hyponatraemia persisted (131 mmol/l). Primary adrenal failure was diagnosed based on flat Synacthen test response: cortisol 198 nmol/l (0 min), 196 nmol/l (30 min) and 212 nmol/l (60 min), elevated ACTH 314 ng/l, and an extremely elevated plasma renin 1110 μ/l (normal 485 mU/l). Investigations into the aetiology showed normal very long chain fatty acids levels excluding X-linked adrenoleukodystrophy, but positive adrenal autoantibodies identifying an autoimmune process. He commenced hydrocortisone and fludrocortisone replacement therapy. At 8-month follow-up there are no obvious neurological or developmental sequelae.
Conclusions: This case illustrates i) the surprisingly young age at which autoimmune adrenal failure can present, ii) important principles of fluid resuscitation in extreme hyponatraemia, iii) differential diagnoses to consider, and iv) that neither normal serum potassium nor detectable random serum cortisol exclude Addisons disease.
09 - 11 Nov 2011
British Society for Paediatric Endocrinology and Diabetes