As a result of advances in high resolution esophageal manometry (HREM), the diagnosis of achalasia can be further divided into manometric subtypes, with impact on treatment response [33, 34]. Although esophageal aperistalsis, poor LES relaxation, and elevation in basal LES pressure are seen commonly across subtypes, distinguishing manometric characteristics allows for further sub-classification. Type 1 is the classic subtype, with absent esophageal pressurization (Fig. 2.3). Type 2 is the esophageal compression subtype, with pan-esophageal pressurization of the esophagus in greater than 20 % of swallows (Fig. 2.4). Type 3 is the spastic subtype, with high amplitude spastic contractions of the esophagus in greater than 20 % of swallows (Fig. 2.5). Distal esophageal peristalsis may be preserved in this subtype, but proximal peristalsis remains absent. A normal esophageal manometric swallow is included for reference (Fig. 2.6).

In candidates with suggestive history or risk factors, chest imaging such as x-ray or CT scan may assist in excluding etiologies of secondary achalasia, including lung cancer, which cannot be identified on the aforementioned testing modalities.

The natural disease course of patients with achalasia that do not receive treatment includes progressive esophageal dilation and tortuosity. In late-stage achalasia, megaesophagus is irreversible and may require esophagectomy [35]. Additionally, an increased risk of squamous cell esophageal cancer has been identified in patients with achalasia, but as the absolute risk is low (with annual incidence of 0.34 %) [36], endoscopic surveillance is not routinely recommended. An association with esophageal adenocarcinoma has also been reported [37]. The pathway has not been elucidated, though it has been proposed that chronic stasis may result in bacterial overgrowth and mucosal dysplasia, leading to the increased cancer risk [38].