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Re: pH-impedance studies have greater clinical utility than pH-monitoring alone.

Dear Sir,

With interest we read the paper by Tighe et al about the use of pH- monitoring in childhood.(1) However, we believe that the authors overestimate the role of this technique and their omission of a detailed discussion of the utility of pH-impedance monitoring renders this review incomplete.

The term ‘gold standard’ can no longer be applied to 24-hour pH- monitoring because pH-probes only detect a minority of gastro-oesophageal reflux (GOR) episodes.(2) Combined pH-impedance monitoring allows for the detection of all reflux (liquid, mixed, gas, acidic, weakly acidic, weakly alkaline). With an increasing body of evidence showing a role for weakly acidic bolus GOR in symptom generation, the measurement of acidity alone provides an incomplete picture of the degree of bolus reflux and the relationship of bolus reflux to symptom episodes. Therefore, symptomatic reflux cannot always be excluded when a pH-study (acid exposure) is normal. The ability to detect bolus reflux, independently of acidity, allows symptomatic reflux to be more accurately detected. Not mentioned in this article, is that there are statistical measures of association between GOR episodes and symptoms (e.g. symptom association probability score). By detecting all bolus reflux, pH-impedance monitoring markedly increases the yield of positive symptom association in infants and children.(3)

In addition, infants with GORD present differently from older children and, as other tests such as upper GI endoscopy are more difficult to perform in infants, the case for invasive functional testing may be greater for infants than older children. In infants, conservative management before any testing or pharmacological therapy is proven effective(4). However, with PPI therapy recently being shown to be ineffective in infants who fail such conservative therapy (5), pH-studies may in fact be justifiable on the basis of establishing acid-related disease when endoscopy is not possible. A recent study in such infants shows that the degree of symptom improvement on esomeprazole correlates with the level of acid exposure off therapy.(6) Nevertheless, the big issue with pH-monitoring is the cut off value of the reflux index used to diagnose pathological acid exposure. The fact remains that no outcome studies testing the value of the reflux index criteria are available. Until they are, clinicians need to be very conservative in interpreting these findings.

We contend that pH-impedance monitoring has greater clinical utility than pH monitoring alone, since it allows for a more complete investigation of reflux and the association of reflux with symptoms.

Sincerely yours,

Michiel P. van Wijk, Clara M. Loots, Taher I. Omari, and Marc A. Benninga

1.Tighe M, Cullen M, Beattie R. How to use: a pH study. Arch Dis Child Educ Pract Ed. 2009 Feb;94(1):18-23.

2.Wenzl TG. Esophageal pH monitoring and impedance measurements: a comparison of two diagnostic tests for gastroesophageal reflux. J Pediatr Gastroenterol Nutr. 2002;34(5):519-23.

3.Loots C, Benninga M, Davidson G, Omari T. Addition of pH-impedance monitoring to standard pH monitoring increases the yield of symptom association analysis in infants and children with gastroesophageal reflux. J Pediatr. 2009;154(2):248-52.

4.Orenstein SR, McGowan JD. Efficacy of conservative therapy as taught in the primary care setting for symptoms suggesting infant gastroesophageal reflux. J Pediatr. 2008;152(3):310-4.

5.Orenstein SR, Hassall E, Furmaga-Jablonska W, Atkinson S, Raanan M. Multicenter, Double-Blind, Randomized, Placebo-Controlled Trial Assessing the Efficacy and Safety of Proton Pump Inhibitor Lansoprazole in Infants with Symptoms of Gastroesophageal Reflux Disease. J Pediatr. 2008; Epub ahead of print.