Neurologic outcome in premature infants with transient asymptomatic hyperammonemia

[Expert consensus on the diagnosis and treatment of neonatal hyperammonemia]

Neonatal hyperammonemia is a disorder of ammonia metabolism that occurs in the neonatal period. It is a clinical syndrome characterized by abnormal accumulation of ammonia in the blood and dysfunction of the central nervous system. Due to its low incidence and lack of specificity in clinical manifestations, it is easy to cause misdiagnosis and missed diagnosis. In order to further standardize the diagnosis and treatment of neonatal hyperammonemia, the Youth Commission, Subspecialty Group of Neonatology, Society of Pediatrics, Chinese Medical Association formulated the expert consensus based on clinical evidence in China and overseas and combined with clinical practice experience,and put forward 18 recommendations for the diagnosis and treatment of neonatal hyperaminemia.

Plasma ammonia concentrations in extremely low birthweight infants in the first week after birth: secondary analysis from the ProVIDe randomized clinical trial

BACKGROUND

Little is known about normative ammonia concentrations in extremely low birthweight (ELBW) babies and whether these vary with birth characteristics. We aimed to determine ammonia concentrations in ELBW babies in the first week after birth and relationships with neonatal characteristics and protein intake.

METHODS

Arterial blood samples for the measurement of plasma ammonia concentration were collected within 7 days of birth from ProVIDe trial participants in six New Zealand neonatal intensive care units.

RESULTS

Three hundred and twenty-two babies were included. Median (range) gestational age was 25.7 (22.7-31.6) weeks. Median (interquartile range (IQR)) ammonia concentration was 102 (80-131) µg/dL. There were no statistically significant associations between ammonia concentrations and birthweight or sex. Ammonia concentrations were weakly correlated with mean total (Spearman's rs = 0.11, P = 0.047) and intravenous (rs = 0.13, P = 0.02) protein intake from birth, gestational age at birth (rs = -0.13, P = 0.02) and postnatal age (rs = -0.13, P = 0.02).

CONCLUSIONS

Plasma ammonia concentrations in ELBW babies are similar to those of larger and more mature babies and only weakly correlated with protein intake. Currently, recommended thresholds for investigation of hyperammonaemia are appropriate for ELBW babies. Protein intake should not be limited by concerns about potential hyperammonaemia.

Neuroanatomical and electrophysiological recovery in the contralateral intact cortex following transient focal cerebral ischemia in rats

Objectives Focal cerebral ischemia may induce synaptic, electrophysiological, and metabolic dysfunction in remote areas. We have shown that the remote dendritic spine density changes and electrophysiological diaschisis in the acute and subacute stages after stroke previously. Here, we further evaluated electrophysiological outcomes and synapto-dendritic plasticity in long-term recovery in the contralateral cortex following focal cerebral ischemia. Methods Male Sprague-Dawley rats were subjected to intraluminal suture occlusion for 90 min or sham-occlusion. Somatosensory electrophysiological recordings (SSEPs) and neurobehavioral tests were recorded each day for 28 days. Postmortem brains were sectioned and subjected to Nissl staining and Golgi-Cox impregnation through a 28-day period following ischemic stroke. Results In the ipsilateral cortex, infarct size in the cortex and striatum was decreased after the subacute stage; the brains showed reduced swelling in the cortex and stratum 3 days after ischemic insults. Dendritic spine density and SSEP amplitude decreased significantly during a 28-day recovery period. In the contralateral cortex, dendritic spine density and SSEP amplitude decreased significantly for 21 days after ischemic stroke, but recovered to baseline by day 28. The deterioration of the dendritic spine (density reduction) in the ischemic cortex was observed; however, this increased neuroplasticity in the contralateral cortex in the subacute stage. Discussion Focal cerebral ischemia-reperfusion induces time-dependent reduction of dendritic spine density and electrophysiological depression in both the ipsilateral and contralateral cortices and intact brain. This neuroanatomical and electrophysiological evidence suggests that neuroplasticity and functional re-organization in the contralateral cortex is possible following focal cerebral ischemia.

Computerized tomography in primary hyperammonemia

Urea cycle enzymopathies are rare in the literature. They are accompanied by neurological disorders somehow related to the increase in blood ammonia. Reviewing the possible physiopathological course we present a case in which during an eight month period severe cerebral atrophy developed, more intense in the occipital region but totally sparing the posterior cranial fossa structures.

When and how should we measure plasma ammonia?

Hyperammonaemia is associated with a high morbidity and mortality. It is important to diagnose as it is often treatable and perhaps, most importantly, may be genetically determined. Measurement of plasma ammonia is rarely necessary in adult medicine. In paediatrics, and particularly in the neonatal period, it is an important investigation in the diagnosis and often in the subsequent management of several inherited metabolic disorders. Patients with these disorders, particularly neonates, will deteriorate over a period of hours and investigation cannot wait. In these situations a plasma ammonia together with other investigations for metabolic disorders must be available urgently and are sometimes necessary out of normal laboratory hours. Interpretation must take into account the age and maturity of the child as well as the clinical state and results of other investigations. If treatment is initiated, frequent monitoring of plasma ammonia may be required. Plasma ammonia can be reliably and conveniently measured using a specific ion-selective electrode system or an automated enzyme method. Screening using a microdiffusion method is not a satisfactory alternative to a quantitative assay. Plasma ammonia is no longer solely the province of the specialised paediatric laboratory, but should be part of the repertoire of every laboratory supporting neonatal or paediatric units. The threshold for accepting requests should be lower than at present if we are to prevent misdiagnoses.