It is usually the first test performed in patients with dysphagia to rule out the presence of a mechanical obstruction secondary to a peptic stricture or cancer. An infiltrating tumor of the gastroesophageal junction can mimic the clinical, radiological, and manometric findings of achalasia, resulting in impaired LES relaxation, esophageal dilatation and absence of peristalsis. This condition, defined as “secondary achalasia” or “pseudo-achalasia,” should be suspected and ruled out in patients older than 60 years of age, with rapidly progressing dysphagia and excessive weight loss. However, these symptoms are not sensitive or specific [7]. When a malignancy is suspected, additional imaging including a CT scan or endoscopic ultrasound should be obtained [8–11].

The endoscopic findings in achalasia patients widely range from a normal exam (in about 33–40 % of patients) [2, 12] to tortuous and dilated esophagus with food retention (Fig. 3.2). The esophageal mucosa can be normal or can present signs of esophagitis (secondary to food stasis or to Candida infection).

Finally, upper endoscopy helps making correct diagnosis of achalasia in patients with a previous erroneous diagnosis of GERD if esophageal dilatation and retention of food and saliva are found.

This test provides information regarding anatomy and emptying of the esophagus. Typical radiologic findings are a narrowing at the level of the gastroesophageal junction, (the so-called bird beak), slow esophageal emptying of contrast with an air- fluid level, and tertiary contractions of the esophageal wall. The diameter, the shape and the axis of the esophagus (dilated and sigmoid in longstanding achalasia), and associated pathology, such as an epiphrenic diverticulum are also defined (Fig. 3.3). All this information is necessary to plan the most tailored approach to the patient with achalasia.

However, the barium swallow may be without abnormalities in about 30 % of cases, particularly in the early stages of the disease. In addition, the expertise of the radiologist with this rare condition is key for a proper interpretation of the radiologic features [12].

Esophageal manometry is the gold standard for the diagnosis of achalasia. Lack of peristalsis and absent or incomplete LES relaxation in response to swallowing are the key criteria for the diagnosis. The LES is hypertensive in about 50 % of patients [2, 13]. However, substantial heterogeneity in terms of peristaltic abnormalities, LES relaxation and esophageal pressure dynamics in patients with achalasia is well known [14, 15].

To date, high-resolution manometry (HRM) is widely used and has superseded in most centers conventional manometry. Briefly, HRM is performed after an overnight fast using a solid-state catheter with 36 circumferential sensors spaced at 1-cm intervals. The probe is inserted trans-nasally, and positioned in order to record from the pharynx to the stomach. Pressure, length, and relaxation of the LES, as well as the pressure of the upper esophageal sphincter (UES) are measured. Esophageal body motility is assessed starting with a basal period without swallowing, followed by 10 wet swallows of 5 ml of water at 30-s intervals. Amplitude, duration and velocity of the peristaltic waves are recorded. When the esophagus is dilated and sigmoid, it may be difficult to pass the catheter through the gastroesophageal junction into the stomach, and fluoroscopic or endoscopic guidance may be necessary.

Pandolfino et al. [16–18] proposed in 2008 a new classification of achalasia according to the manometric patterns of esophageal body contractility by high-resolution manometry: type 1, classic, with minimal esophageal pressurization; type 2, achalasia with pan-esophageal pressurization; and type 3, achalasia with spasm (Figs. 3.4 and 3.5). Type 2 achalasia patients are significantly more likely to respond to any form of treatment than type I or type 3 patients [17, 19]. At logistic regression analysis type 2 was found to be a predictor of positive treatment response, whereas type 3 was predictive of negative treatment response [17].

This test is recommended in selected untreated patients when the diagnosis is uncertain, in order to distinguish between GERD and achalasia.

Briefly, the pH probe is calibrated in a buffer solution at pH 7 and 1 before and after the test. The monitoring is performed after discontinuing acid-suppressing medications 10 days (proton pump inhibitors) or 3 days (histamine-2 receptor antagonists) before the study. The dual-channel pH catheter with two sensors located 15 cm apart is placed trans-nasally so that the distal and the proximal sensors are positioned respectively 5 cm and 20 cm above the upper border of the manometrically determined LES. Patients are encouraged to consume an unrestricted diet during the study, but to avoid snacks and carbonated beverages in between meals. Gastroesophageal reflux is evaluated in terms of (1) number of reflux episodes; (2) number of episodes longer than 5 min; (3) duration of the longest reflux episode; (4) acid exposure (percentage of time with pH less than 4); and (5) esophageal acid clearance (mean duration of a reflux episode) in total, in the distal and proximal esophagus, in the supine and upright position. Data are integrated into the DeMeester score, with a value greater than 14.7 set as abnormal [20].