The differential diagnosis of hypernatraemia in children, with ...

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The Diagnosis of Salt Poisoning Leading to Hypematraemia in Children – September 2009 • Craniopharyngioma is the most common space occupying cause, with or other tumours such as optic glioma 112 being seen less frequently. Germinoma is an important cause in older children. It is seen in a significant proportion of children with Langerhans’ cell histiocytosis. Other rare infiltrative causes include Hodgkins disease, leukaemias and sarcoidosis. • Idiopathic diabetes insipidus without recognisable CNS malformation 113 is a common cause, where autoimmune factors may be important. • Associated with CNS malformations especially septo-optic dysplasia 114 and holoprosencephaly, hydranencephaly or arhinencephaly 115-121 . • Following severe brain injury 122 hypoxic damage 123 intracranial haemorrhage 124 , and carbon monoxide poisoning 125 . • It can be familial, presenting at different ages. • It can be associated with hypothyroidism and learning difficulties in the Schinzel-Giedion syndrome 126 . In a child with hypernatraemia a urine osmolality can assist in excluding diabetes insipidus (grade D). This is best interpreted in conjunction with a simultaneous serum osmolality: children with long-standing hypernatraemia in association with diabetes insipidus (cranial or nephrogenic) can generate relatively high urine osmolalities because of volume contraction and reduced glomerular filtration rate. Evidence statement In a child with hypernatraemia a urine osmolality can assist in excluding diabetes insipidus (grade D). The water deprivation test has a suboptimal sensitivity and specificity, and should be interpreted alongside the history, baseline biochemistry and general context. The diagnosis can be made following an assessment that may include the water deprivation test, with a response to the administration of DDAVP. The survey of hypernatraemia in children from Texas 23 found that 9 of 68 (13%) of children with hypernatraemia (in the majority of whom it was hospital acquired) had central diabetes insipidus and this was the main cause of excessive urinary water loss. 29
The Diagnosis of Salt Poisoning Leading to Hypematraemia in Children – September 2009 Nephrogenic diabetes insipidus The group of conditions called nephrogenic diabetes insipidus (NDI) have in common polyuria and polydipsia secondary to renal resistance to the action of vasopressin, in contrast to central diabetes insipidus where there is lack of vasopressin release. Some people use the term NDI to mean only the genetically determined forms of the disease (due to mutations in the gene for the V 2 vasopressin receptor 127 , the X-linked variety 128 , and to mutations in the gene for the water channel aquaporin 2, the autosomal recessive variety 129, 130 ), whereas others use it more broadly to include impairment of urinary concentrating ability due to diseases of the renal medulla such as nephronophthisis, sickle cell disease, reflux nephropathy and analgesic nephropathy. The distinction from central diabetes insipidus is the lack of response to DDAVP. The survey of hypernatraemia in children from Texas 23 found that 3 of 68 (4%) of children with hypernatraemia had nephrogenic diabetes insipidus. Renal medullary damage Conditions or drugs affecting renal medullary function may result in excessive renal water loss. These include: • Renal disease (renal dysplasia, medullary cystic disease, reflux nephropathy, polycystic disease) • Systemic disease with renal involvement (sickle cell disease, sarcoidosis, amyloidosis, methylmalonic acidaemia) • Drugs (amphotericin, phenytoin, aminoglycosides, methoxyflurane, and possibly high doses of Ticarcillin and carbenicillin) Strictly speaking, these should all be considered as examples of acquired vasopressin resistant, nephrogenic diabetes insipidus. Although there is a report of children with hypernatraemia secondary to urinary tract infection 131 , it is likely that the cause was increased water loss due to fever and reduced intake due to malaise with or without vomiting. Investigation is as for diabetes insipidus. 30
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The differential diagnosis of hypernatraemia in children, with ...

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