The first category in the Chicago Classification is incomplete LES relaxation, which includes achalasia and EGJ outflow obstruction. Achalasia is defined as the absence of esophageal peristalsis with incomplete LES relaxation. In the Chicago Classification, the diagnosis of achalasia is based on an elevated median IRP in combination with failed peristalsis or spasm.[3] The IRP is a measure of the relaxation of the EGJ, with typical values (less than 15.0 mmHg), although this is catheter specific.[10] During normal swallows, the LES at the EGJ relaxes to allow the food bolus into the stomach. If the LES fails to relax, this is indicated by elevated IRP. The IRP is a software mean calculation of the EGJ pressure in the lowest 4 seconds of the 10-second swallow after UES opening.[3]

If patients have an IRP greater than the upper limit of normal (ULN) along with failed peristalsis or a spasm, then they are considered to have achalasia. Achalasia is then further divided into three distinct subclasses based on the pattern of contractility in the esophageal body. In type I (classic achalasia), no pressure waves are recorded in the distal esophagus as there is 100% failed peristalsis. Failed peristalsis is defined by DCI less than 100 mmHg cm/s for type I achalasia.[11] Type II is characterized by at least 20% pan-esophageal pressurizations with no normal peristalsis. Type II achalasia is the most prevalent subtype of achalasia.[12] These patients may have a distal latency of under 4.5 seconds, but the diagnosis of type II achalasia is dependent on >20% swallows with pan-esophageal pressurizations.[3] In Type III, at least 20% of swallows reveal rapidly propagating or spastic simultaneous contractions with a distal latency of below 4.5 seconds and no normal peristalsis.[3][9] These spasms are typically distal on the esophageal body and do not have the pan-esophageal pressurizations seen with type II achalasia. If patients have high IRP, indicating failed LES relaxation, with weak peristalsis or do not fit into achalasia subclasses I-III, then they are considered to have EGJ outflow obstruction. EGJ outflow obstruction is largely a manometric diagnosis but has a rising incidence after the advent of HRM.[13]

The second category of the Chicago Classification is major disorders in peristalsis, which include distal esophageal spasm, hypercontractile or jackhammer esophagus, and absent peristalsis. Distal esophageal spasm (DES) is diagnosed on HRM in patients with normal IRP, normal DCI, but distal latency less than 4.5 seconds. Distal latency is measured from the UES swallow induced relaxation to the contractile deceleration point (CDP). Normal distal latency is greater than 4.5 seconds, with anything shorter than 4.5 seconds is considered esophageal spasm. The CDP is the point on which peristaltic wave velocity slows, demarcating peristalsis from ampullary emptying.[3][9] The normal CDP is within 3 cm of the LES. The HRM software calculates the CDP and distal latency.

Hypercontractile or jackhammer esophagus is defined as having a distal contractile integral (DCI) of more than 8000 mmHg cm/s.[14] DCI is a multiplication of length, duration, and amplitude of contractions. Basically, it is the force of peristalsis. A DCI less than 450 mmHg cm/s indicates weak peristalsis, whereas a DCI higher than 8000 mmHg cm/s indicates hypercontractile peristalsis.[15] Asymptomatic controls rarely have a DCI greater than 8000 mmHg cm/s, and therefore ≥20% of swallows with a DCI more than 8000 mmHg cm/s is required for a diagnosis of jackhammer esophagus.[9] Patients with hypercontractile esophagus typically have normal IRP and distal latency, which excludes achalasia and distal esophageal spasm.

Absent contractility is when there is a complete failure of peristalsis with normal IRP. These patients typically have a DCI of less than 100 mmHg cm/s.[3] These patients are often diagnosed with a systemic autoimmune rheumatological disorder, such as systemic scleroderma.[16] The absent contractility also predisposes these patients to have symptomatic gastroesophageal reflux. If patients have borderline elevated IRP, they may be considered to have type I achalasia.[9]

The third category of the Chicago Classification is minor disorders of peristalsis, which include ineffective esophageal motility or fragmented peristalsis. Ineffective esophageal motility is diagnosed when >50% of swallows are ineffective, as defined by failed (DCI of less than 100mmHg cm/s) or weak (DCI 100 mmHg cm/s to 450 mmHg cm/s) peristalsis.[3] These patients have normal IRP and distal latency. Fragmented peristalsis is defined as >50% of swallows with a large break (>5 cm) between peristaltic contractions and not having ineffective esophageal motility.[3]

Minor disorders of peristalsis are conditions with impaired esophageal bolus transit. The clinical validity of these manometric diagnoses has come under question. Often, patients diagnosed with minor disorders of peristalsis report minimal symptoms and have good long-term outcomes.[17] Furthermore, minor disorders of peristalsis can be seen in asymptomatic, normal control subjects, unlike major disorders of peristalsis or incomplete LES relaxation.[17] Finally, the term “nutcracker esophagus” use to be defined as DCI 5000 mmHg cm/s to 8000 mmHg cm/s.[3] However, this term is no longer used as it has little clinical significance.[3]

The fourth category of the Chicago Classification is normal esophageal manometry. These patients have normal IRP (greater than 15 mmHg), normal distal latency (more than 4.5 seconds), and DCI between 450 mmHg cm/s to 8000 mmHg cm/s. Normal esophageal manometry is typically diagnosed in the preoperative workup for gastroesophageal reflux surgery. Of note, patients only need >50% effective swallows to be considered normal.[3]

There are several interfering factors with the interpretation of HRM. Patients who undergo the procedure must stop certain medications, including H2-blockers, proton pump inhibitors, calcium channel blocks, nitrates, opioids, sedative medications, and even caffeine.[4] If patients have undergone previous esophageal surgeries including gastric fundoplication, Heller myotomy, per-oral esophageal myotomy (POEM), pneumatic dilations (PD), or even botulinum injections, these may falsely alter the findings on HRM.[4] Finally, patients with large hiatal hernias or peptic strictures may have false HRM findings.[18]

Complications of HRM are rare. Placing the HRM nasogastric sensory catheter may cause discomfort in the nose or throat. During placement of the catheter, patients may experience a gagging sensation that may lead to emesis. Caution should be exercised when placing the catheter in patients who have recently had esophageal surgery or in patients with esophageal varices. Finally, there have been rare instances of esophageal perforation in patients with severe achalasia during HRM.[19]

Patients should meet with their clinician before the procedure to explain the rationale and expectations during HRM. Following the procedure, patients and clinicians should meet to discuss findings, treatment options, and answer any questions. The procedure itself can be uncomfortable. It is important to educate the patient before the procedure on what they can expect. 

Based on the findings on HRM, patients were stratified by the Chicago Classification into four different classifications of esophageal motility disorders. Individualized treatment plans for patients with different esophageal motility disorders need to be implemented. These treatments include pharmacologic, endoscopic, and surgical options.

Patients with esophageal motility disorders who are older, frail, and have multiple comorbidities may best be treated by pharmacologic therapies, including calcium channel blockers and nitrates. Although the efficacy of these medications is low, it may offer some relief for non-surgical candidates.[20] Furthermore, patients with EGJ outlet obstruction or minor disorders of peristalsis may best be treated with pharmacologic therapy.[21]

Patients who are better surgical candidates but want to try non-surgical options may undergo endoscopic injection of botulinum toxin or endoscopic PD. After botulinum injections, patients initially may have symptom relief similar to endoscopic PD or surgical myotomy; however, the inhibitory toxin weakens after several months and repeat injections as often required.[22] PDs are more durable long term than pharmacologic treatments. Furthermore, PD has been shown to be similar to laparoscopic Heller myotomy with fundoplication (LHM) in terms of therapeutic success.[23][24] Therefore, PD is typically the initial treatment for achalasia, especially in type II achalasia.[20] Although PD is effective for patients with type I achalasia and absent contractility, patients treated with surgery have similar, more durable outcomes.[20]

LHM or POEM is the standard surgical treatment for esophageal motility disorders. Typically, patients are referred to surgery after failed PD. Both LHM and POEM have similar efficacy for symptom abatement after surgery, although higher rates of gastroesophageal reflux are reported after POEM.[25] LHM is better studied and more available in the general population, making it the most common operation for all esophageal motility disorders. Although all types of esophageal motility disorders can undergo surgery first, patients with achalasia type III, jackhammer esophagus, and distal esophageal spasm typically have better response rates with surgery compared to PD.[26] Moreover, patients with spastic esophageal disorders and absent peristalsis may benefit more from POEM than LHM, due to POEM allowing a longer esophageal myotomy compared to LHM.[26] Finally, surgery can be considered in all esophageal motility disorders in suitable candidates who have failed conservative treatments.