I read the recent case
report(1) on this subject with interest. The authors have discussed a
neonate with breast-feed mal-nutrition related hypernatremia. Many
features of the index case however do not fit into this entity and
require clarifications:
1. Inadequate breast milk
production is the most important factor in the pathogenesis of this
entity(2) No comment has been made regarding the adequacy of milk
production. Authors have mentioned that normal urine output, as in this
case, could not be the only criteria for adequacy of breast-feeding and
factors like weight loss and dehydration should also be valuated. As
conditions like diabetes insipidus (DI) can also lead to weight loss and
dehydration, these criteria cannot be a surrogate to inadequate breast
milk production.
2. Hypernatremia in this
case has been attributed to dehydration and thereby should have been
associated with concentrated urine. How do authors explain extremely low
urinary osmolality (61 mOsm/kg) and specific gravity (1005) in this
case, a finding that excludes the diagnosis of dehydration due to
decreased breast milk production?
3. Excessive weight loss,
hypernatremia, elevated serum osmolality, normal urine output,
dehydration and low urinary osmolality in this case strongly suggest the
diagnosis of DI. The authors have mentioned that fluid deprivation test
ruled out central and nephrogenic DI. A few points however require
clarifications: (a) Serum osmolality decreased from 294 mOsm/kg
to 290 mOsm/kg after fluid deprivation! How do the authors explain a
decrease in serum osmolality (instead of an expected increase) after a
period of fluid deprivation?; (b) Criteria for termination of
water deprivation test include weight loss >5%, serum osmolality
>300 mOsm/kg, serum sodium >150 mOsm/L or a urine osmolality
>800 mOsm/L(3). In this case fluid deprivation was terminated
prematurely (serum osmolality 290 mOsm/L). The authors state that normal
urinary osmolality after fluid deprivation (320 mOsm/kg) and vasopressin
administration (397 mOsm/kg) excluded DI. Contrary to these conclusions,
these findings (urinary osmolality <800 mOsm/L after water
deprivation and vasopressin administration) are suggestive of
nephrogenic DI(4); and (c) There is marked discrepancy between
measured (294 mOsm/kg) and calculated osmolality (466 mOsm/kg, as
calculated from the laboratory data provided). What explanations do the
authors offer?
4. Authors mention that
the neonate went into shock after vasopressin injection (severe enough
to require fluid boluses and dopamine). It is difficult to understand
how vasopressin, a vasopressor, could have led to shock in the already
dehydrated neonate. This point needs to be emphasized, as fluid
deprivation is not only required but also potentially hazardous under
such circumstances. Hypernatremia (Na >150 mEq/L) and elevated serum
osmolality (>300 mEq/L) in the presence of low urine osmolaity
(<400 mOsm/kg) are sufficient to diagnose DI and fluid deprivation is
not required.
5. Breast milk sodium
levels should be estimated in all breast fed neonates with hypernatremia
as elevated breast milk sodium is an important factor contributing to
hypernatremia(5). This also has implications in the decision of
restarting breast-feeding, which should be initiated only when the
breast milk sodium levels have become normal. Non-availability of breast
milk sodium in this case thus poses limitations regarding diagnosis and
management.