Which diagnostic step not included should be performed with suspected Chagas disease affecting esophageal motility?

In the context of diagnosing Chagas disease, particularly when esophageal motility is suspected to be affected, the barium swallow study is a key diagnostic tool. This imaging study allows for the evaluation of the esophagus's structure and function by visualizing how well it is able to move a barium-containing solution from the throat to the stomach. In Chagas disease, the characteristic involvement of the esophagus can lead to dilation and impaired peristalsis, which can be effectively observed through this study.

The other diagnostic steps, while also useful in different contexts, do not offer the same direct insights into esophageal motility. An esophageal biopsy may be indicated to rule out other conditions but does not assess motility. A CT scan of the thorax provides imaging but is less specific for esophageal dysfunction associated with Chagas disease. Esophageal manometry is indeed utilized to evaluate motility but may not provide the initial imaging needed to identify structural changes and motility issues.

Thus, the omission of the barium swallow as a diagnostic step is significant, as it directly aids in visualizing the effects of Chagas disease on esophageal motility, making it a vital investigation in this scenario.