Neonatal hepatitis is a default diagnosis reached after excluding other more specific causes of prolonged neonatal cholestasis. The purpose of this brief review is to highlight the expanding spectrum of diagnoses causing prolonged neonatal cholestasis of infancy and to address emerging clinical dilemmas about the role of conventional clinical tests such as liver biopsy or dynamic hepatobiliary scintigraphy in the new era. Novel entities and overlapping metabolic conditions are listed, with a hope to increase awareness of practising paediatricians and direct more specific investigations.
- Neonatal hepatitis is a diagnosis of exclusion in prolonged cholestasis of infancy and its prevalence has more than halved in recent years.
- The reduction is due to advances in biochemical and genetic diagnosis of inherited and metabolic conditions with overlapping clinical presentation in early infancy.
- Paediatricians need to look for additional clinical signs, such as ichthyosis, hypertrichosis, cutis laxa, skeletal changes, or congenital deafness, which could point to new conditions emerging in the spectrum of prolonged neonatal cholestasis.
- Role of liver biopsy needs to be redefined to exploit genetic and immunohistochemical progress, while the dynamic hepatobiliary radionuclide studies are much less useful in the diagnosis due to poor specificity.
- The more sophisticated noninvasive diagnostic investigations are becoming more affordable and are likely to challenge the roles of standard diagnostic methods in the near future.
The latest guidelines for management of neonatal cholestasis were published by NASPGHAN more than 10 years ago (1). Available database information (PubMed, MEDLINE) was searched for terms: neonatal hepatitis (NH), neonatal cholestasis, prolonged conjugated hyperbilirubinaemia, hepatobiliary scintigraphy, and liver biopsy.
NH is usually defined as a syndrome where extensive investigations into anatomic, genetic, or metabolic causes of prolonged neonatal cholestasis (PNC) in neonates have failed to provide an explanation. Often it is, however, neither “neonatal,” as diagnostic investigations usually extend well into early infancy, nor “hepatitis” because biochemical or histopathological features only exceptionally suggest a significant liver inflammation. To add to this semantic conundrum, attributes such as nonspecific, idiopathic, or cryptogenic are often attached to NH. Thanks to the wider availability and lower cost of genetic testing, an increasing number of paediatric liver conditions have become identifiable early in life. The main reason for reducing the proportion of NH in PNC of infancy was the detection of various inherited autosomal recessive causes of familial cholestasis responsible for prolonged hyperbilirubinaemia of infancy. They are listed and referenced in Table 1(2–28), although this compilation is by no means exhaustive.
The prevalence of NH is estimated to be 1 in 2500 live births (29). Recent meta-analysis analysed 17 larger studies including 1692 infants with PNC of infancy and suggested that NH and biliary atresia (BA) each represented around 26% of cases, whereas the remaining half included infection (11%), total parenteral nutrition–associated cholestasis (6%), metabolic disease, alpha-1-antitrypsin deficiency, and perinatal hypoxia/ischemia (4% each) (29). Galactosaemia was the commonest metabolic condition (37%), whereas cytomegalovirus accounted for 32% of the infections. It is interesting that some half a century ago, a single-tertiary centre prospective study of 137 infants found an almost identical proportion of infants to have BA (24%), whereas NH was “diagnosed” in 69% of non-BA children; alpha-1-antitrypsin deficiency was responsible for a majority (75%) of 7% of the identifiable causes (30).
Role of Hepatobiliary Scintigraphy
With regards to the diagnostic work-up of infants with PNC, the most pressing clinical issue is to either demonstrate or to exclude underlying anatomical problems such as BA or congenital choledochal malformations. Patients with BA who undergo their corrective biliary surgery earlier have much better chances of an improved outcome (31). For many years dynamic hepatobiliary radionuclide studies assessing the uptake and excretion of isotopes such as Tc-99 m-labelled iminodiacetic acid and its derivatives have been an important part of the work-up for PNC of infancy. Recent meta-analysis assessed 81 studies using this modality to distinguish NH from BA (32). The authors confirmed a good sensitivity (overall 98.7% range, 98.1%–99.2%), but a poor specificity (overall 70.4%, range, 68.5%–72.2%) of this test. This data questions its non-selective use for patients with children with PNC as this investigation appears not to be specific enough and adds little to the simple clinical observation of stool colour. It comes as no surprise that the premedication for testing improved the test specificity (phenobarbitone [72.2%], phenobarbitone and cholestyramine [70.8%], and ursodeoxycholic acid [84.8%]) (32). It is, however, noteworthy that a retrospective study from India reported a significant improvement in accuracy of demonstrating the patency of biliary tree (36% vs 18%) when betamethasone was added to phenobarbitone as premedication (33). Formal studies for distinguishing different nonanatomical causes of NH have not been reported, but are likely to be even more difficult to set up and interpret. Overall, it appears that the current role of hepatobiliary radionuclide studies in this setting has been considerably diminished.
Role of Liver Biopsy
Many (although not all!) paediatric liver centres use percutaneous liver biopsy in their initial diagnostic work-up to establish whether the clinical suspicion of BA is strong enough to warrant performing intraoperative cholangiography followed by Kasai portoenterostomy, if indicated. Histologically, NH is commonly associated with giant cell hepatitis, combined with different degrees of portal and lobular inflammation, canalicular cholestasis, bile duct reduplication, extramedullary haemopoiesis, and mild fibrosis (34). The role of liver biopsy is being re-evaluated due to its perceived invasive nature (35), but also in the light of emerging diagnostic technologies, such as whole genome/exome sequencing proteomics (36) or metabolomics (37). With standard precautions in place, the liver biopsy is safe and still remains the most reliable and rapidly informative diagnostic tool in paediatric hepatology (35). Presence of microvesicular or macrovesicular steatosis, prominent macrophages, or damaged mitochondria could assist in arranging further tests for suspected metabolic conditions. With added immunohistological and in situ genetic investigations it potentially not only points to further diagnostic steps, but also could contribute to unravelling of pathogenesis, which have been proven instrumental in defining and advancing our understanding of progressive familial cholestasis syndromes (36). Therefore, progress in genetic medicine needs to be integrated into a comprehensive immunohistochemical work-up if a key diagnostic role of the liver biopsy is to be maintained.
The commonest single cause for PNC remains BA, which occurs sporadically. Many of the conditions associated with neonatal cholestasis will, however, often have overlapping clinical, biochemical, and even histological features. In the context of consanguinity or familial recurrence of NH, additional effort should always be made to try to decipher the aetiology, which may well be genetic or metabolic. In the era of increasingly laboratory-dominated medicine there is a risk that conventional clinical assessment may be deemed less relevant. Our view is that there is still no substitute for an observant paediatrician detecting more subtle clinical signs, reporting, and correlating them with the sophisticated biochemical and genetic investigations and available literature.
Many clinicians have noted the relevance of pursuing further genetic investigations, in particular when low levels of serum gamma-glutamyl transpeptidase are seen in a cholestatic infant (38). These children are generally thought to have less good prognosis, in contrast with the others with NH, where no cause is identified. Attempts to correlate the outcome of certain cholestatic conditions with the serum gamma-glutamyl transpeptidase levels at presentation have had mixed success, possibly due to a number of physiological confounding factors, such as gestational age, birth weight, lack of enteral feeding, but also regional ethnic, metabolic or cultural differences, and so on (39). New challenges for attending paediatric hepatologists are to be aware of and to link clinical signs, seen in some of these newly described associations, with NH. For example, cutis laxa or hypertrichosis in transaldolase deficiency (10), severe eczema in neonatal ichtyosis-sclerosing cholangitis syndrome (19), extrahepatic manifestations such as deafness, chronic diarrhoea in familial intrahepatic cholestasis-1 disease (2) or TJP2 deficiency (7), or bone changes in arthrogryposis-renal dysfunction-cholestasis (8,9) syndrome could be the clues for accurate diagnosis. This awareness could facilitate the direction of specific biochemical and genetic investigations until the time when so-called “neonatal cholestasis genetic panels” become reliable, affordable, and comparable. Additional desirable feature of the genetic tests should be their rapid turnover, which would secure them a place in the time-constrained algorithm for the differentiation of BA from other causes.
It is tempting to speculate that in such a diverse area of PNC of infancy, the emerging sophisticated diagnostic methods based on ultraspecific identification of altered metabolic pathways and specific biomarkers could play a contributory role (40). Metabolomics, for example, using proton nuclear magnetic resonance spectroscopy, could detect compounds related to genetic modification or pathophysiological stimuli (41). Zhao et al used liquid chromatography-tandem mass spectrometry to assess metabolite differences between NH, BA, and controls, and concluded that serum threonine levels were higher in the infants with NH (37). Zhou et al suggested that infants with NH have lower taurochenodeoxycholic acid and higher chenodeoxycholic acid levels than those with BA (42). In contrast, 1 earlier study from the UK could not demonstrate differences on the neonatal blood spots between NH and other forms of PNC of infancy (43). Currently, there are no reliable noninvasive markers to distinguish BA from other causes of PNC in early infancy. It appears that at present time we are not yet able to translate the exciting developments in laboratory technologies to clinical paediatric hepatology practice.
We anticipate that in the not too distant future it will be possible to perform a genetic panel for neonatal cholestasis which will be inexpensive, rapid, and comprehensive enough to detect the majority of mutation-related conditions. Even now there are centres where large-scale testing such as whole genome or whole exome sequencing could be performed at acceptable costs. This will undoubtedly improve and refine diagnostics and further reduce the reported prevalence of the NH syndrome. Performing such extensive genetic tests in young infants will, however, bring about complex ethical and legal issues, which will need to be fully clarified before their definite implementation. Finally, as the heterozygous states within the spectrum of progressive familial cholestasis have been associated with transient PNC and benign outcome (44,45), it remains conceivable that underlying isolated or combined genetic variations and even polymorphisms for some other existing or yet unidentified inherited disorders could play a role during this physiologically challenging period of early infancy. Thus, the clinical relevance of certain types of mutations, carrier states, and genetic polymorphisms will need ongoing future study.
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