Relationship between baseline impedance levels and esophageal mucosal integrity in children with erosive and non-erosive reflux disease O. BORRELLI ,* S. SALVATORE,  V. MANCINI , à M. RIBOLSI ,§ M. GENTILE, – B. BIZZARRI ,** M. CICALA,§ K. J. LINDLEY*& G. L. DE’ANGELIS** *Department of Gastroenterology, Neurogastroenterology and Motility Division, Great Ormond Street Hospital for Sick Children, London, UK  Department of Paediatrics, University of Insubria, Varese, Italy àDepartment of Pediatrics, Division of Pediatric Gastroenterology, ‘‘La Sapienza’’ University of Rome, Rome, Italy §Department of Digestive Disease, Campus Bio Medico University of Rome, Rome, Italy –Department of Molecular Biology, ‘‘La Sapienza’’ University of Rome, Rome, Italy **Division of Pediatric Gastroenterology, University of Parma, Parma, Italy Abstract Background Baseline impedance measurement has been reported to be related to esophageal acid expo- sure and hypothesized to be a marker of microscopic changes of the esophageal mucosa. Aims of the study were to establish whether any relationship existed between the magnitude of intercellular space diameter (ISD) of esophageal mucosa and baseline impedance levels in children with gastro-esophageal reflux dis- ease (GERD), and to compare baseline impedance levels between children with non erosive (NERD) and erosive (ERD) reflux disease. Methods Fifteen children (median age: 11.2 years) with NERD, and 11 with ERD (median age: 9.6 years) were prospectively studied. All patients underwent upper endoscopy. Biopsies were taken 2–3 cm above the Z-line, and ISD was measured using transmission electron microscopy. All patients underwent impedance pH-monitoring, and baseline impedance levels were assessed in the most distal impedance channel. Key Results Mean (±SD) ISD did not differ between NERD (1.0 ± 0.3 lm) and ERD (1.1 ± 0.3 lm, ns). Considering all patients together, no correlation was found between distal baseline impedance and ISD (r: )0.15; ns). Conversely, negative correlations were found between distal baseline impedance and acid exposure time (r: )0.76; P < 0.001), long-lasting reflux episodes (r: )0.78; P < 0.001), acid reflux episodes (r: )0.62; P < 0.001), and acid clearance time (r: )0.79; P < 0.001). Distal baseline impedance was significantly lower in ERD [1455 (947–2338) W] than in NERD children [3065 (2253–3771) W; P < 0.01]. Conclusions & Inferences In children with GERD baseline impedance levels are not useful in predicting reflux-induced ultrastructural changes in the esophageal mucosa, despite their abil- ity to discriminate between NERD and ERD. Keywords baseline impedance, children, erosive reflux disease, gastro-esophageal reflux disease, intercellular space diameter, multichannel intraluminal impedance test, non-erosive reflux disease. INTRODUCTION Gastro-esophageal reflux disease (GERD) is one of the most common causes of foregut symptoms in pediatric age group. The estimated prevalence of symptoms occurring at least once a week ranges between 2% and 8%. 1 As in adults, childhood GERD encompasses a large spectrum of disease severity, and non-erosive reflux disease (NERD) is the most common phenotype accounting for up to 80% of patients. 2,3 Over the last few years, studies in both adults and children have shown that, beside other histological Address for Correspondence Osvaldo Borrelli, MD, PhD, Division of Neurogastroenterol- ogy and Motility, Department of Paediatric Gastroenterol- ogy, Great Ormond Street Hospital for Sick Children, Great Ormond Street, WC1N 3HZ London, UK. Tel: +44(0)20 7405 9200 (ext. 5971); fax: +44(0)20 7813 8382; e-mail: borreo@gosh.nhs.uk Received: 2 March 2012 Accepted for publication: 1 May 2012 Neurogastroenterol Motil (2012) doi: 10.1111/j.1365-2982.2012.01947.x Ó 2012 Blackwell Publishing Ltd 1 Neurogastroenterology & Motility