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therapy, impedance testing results
on
therapy cannot be
predicted from customary baseline parameters, except
among patients with esophagitis in whom the correlation
was weak at best, with only 19% of the population hav-
ing esophagitis. Our data suggests that impedance
parameters
on
therapy do not correlate well with any
reflux parameters previously employed to assess disease
severity. Thus, we urge caution regarding the over-inter-
pretation of impedance parameters, as the clinical
relevance of impedance testing remains unclear at this
time.
The presence of non- or weakly acidic reflux in
patients on PPI therapy is suggested to imply continued
reflux and the need for additional therapies.
10,11
In a
group of 19 patients who had positive symptom associa-
tion with acid or nonacid reflux on impedance testing, a
retrospective phone interview study suggested 94% fun-
doplication success.
23
However, two recent prospective
trials have questioned the clinical reliability of symptom
indices in reflux disease.
24,25
Furthermore, the most
recent surgical trial in patients with extraesophageal
syndrome showed that impedance parameters
on
ther-
apy did not
predict
symptom response
postfundoplication.
26
In this study, the traditional pa-
rameters of increased acid exposure, presence of hiatal
hernia, and typical reflux symptoms (heartburn and re-
gurgitation) were predictive of extraesophageal symptom
response to fundoplication.
Important controversy in patients with continued
symptoms, despite aggressive PPI therapy, is whether to
conduct testing
on
or
off
PPI therapy. Employing both
impedance-pH monitoring
on
therapy and wireless pH
monitoring
off
therapy in the same group of patients
with PPI-refractory symptoms, we confirmed that non-
or weakly acid reflux may be present in up to 35% of
patients; however, continued acid reflux was not seen in
any patient. Our data are in agreement with two prior
studies; one showing that continued acid reflux is a rar-
ity on twice daily PPI therapy,
27
and the other showing
continued nonacid reflux by impedance testing in 37% of
patients refractory to PPI therapy.
12
More important, we
could not identify any
off
therapy traditionally employed
physiologic parameter that could predict the
on
therapy
impedance findings. Furthermore, patients with more
severe reflux by pH testing defined as % time pH
<
4 of
greater than 10% had similar impedance parameters
than those with no or mild reflux at baseline (Fig. 4).
Thus, it appears that the impedance parameters do not
correlate with any of the traditionally employed tools in
assessing reflux severity. For example, it has been
shown that patients with hiatal hernia typically have
higher reflux scores compared to those without hiatal
hernia,
28
esophagitis severity is expected to correlate
with hiatal hernia size and esophageal acid exposure,
29
and % time pH
<
4 increases in a graded fashion across
the GERD spectrum.
30
Thus, given the lack of any corre-
lation between impedance results and these traditional
markers, we urge caution regarding the clinical rele-
vance of impedance testing.
Our study is unique in that the same patient popu-
lation underwent physiologic testing off and on PPI
therapy. However, some limitations of our study should
also be highlighted. First, the results from our study
underscore the need for larger outcome studies among
patients with refractory symptoms and abnormal imped-
ance testing. Second, our present analysis discusses the
impedance findings with respect to abnormal number of
reflux events in the distal esophagus. We did not evalu-
ate proximal extent and liquid, gas, or mixed nature of
the refluxate, as some believe may be important in a
subgroup of treatment-resistant patients.
31
Additionally,
we have used number of reflux events as the primary
measure as opposed to SI or SAP. However, the use of SI
and SAP is problematic in this group since patients have
already declared lack of clinical response to aggressive
acid suppression, and recent studies suggest that these
metrics may not be reliable or reproducible.
24,25
CONCLUSION
In a unique group of patients who had both
off
ther-
apy traditional esophageal physiologic testing and
on
therapy impedance monitoring, our study shows limited
correlation between the latter results with the former
previously recognized and employed methodologies.
There remains uncertainty regarding the clinical utility
of impedance testing among patients with extraesopha-
geal symptoms, and we recommend caution in over-
interpretation of impedance pH monitoring data.
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Fig. 4. Impedance parameters dichotomized by severity of base-
line acid reflux. The impedance parameters were no different in
those with no or mild reflux (defined as % total time pH
<
4 of
less than or equal to 10%) compared to those with moderate to
severe reflux (
>
10% acid reflux).
Laryngoscope 123: October 2013
Kavitt et al.: The Role of Impedance Monitoring in Extraesophageal Symptoms
143