Review of Rami Sweis’ “Update on Chicago Classification for HRM and its Implication for Motility Testing” (DDF Conference, 2015)
Dr. Rami Sweis is part of the working group that has recently updated the Chicago Classification of oesophageal motility disorders (1) which is now in its third iteration since the original 2008 study (2). Spurred by the introduction of a full oesophageal length, high-resolution set up and the representation of the acquired data as a topographical contour plot, there has been both praise and criticism of the classification’s use in physiology.
Summary of v3.0
The lecture provided incite as to how to apply the classification which has now emphasised the separation of GOJ obstruction, major and minor peristaltic disorders. As Dr. Sweis explained, this prioritisation was made because pathology at the GOJ almost always leads to problems in the oesophagus and, along with the major peristaltic disorders, is found to frequently require interventional therapy.
GOJ Outflow Obstruction
A change to recording the median rather than mean IRP has been made in this version, as outlier values were seen to skew the result. It is useful to remind that IRP measures only the lowest pressures during the relaxation period, meaning that contribution by the crura can be minimised, allowing for high specificity and sensitivity for achalasia (3). It was also noted that different sensor types have separate normalised values and care must be taken that this distinction is made (1).
The definitions of the three achalasia subtypes have remained largely similar. The issue of achalasia with normal IRP had been raised before v3.0 was published (4) but a caveat has been included now to consider achalasia where there is 100% failed peristalsis and a borderline IRP (10-15mmHg) or where there is evidence of oesophageal compression. The presenter suggested that normal IRP achalasia may be due to the fact that a registerable resistance caused by outflow obstruction requires a large enough proximal compression which may not be possible with only 5ml of water in a dilated oesophagus. Additionally spastic achalasia has been restricted to premature contractions rather than including ‘fragments of distal peristalsis’ as was seen in v2.0 (5). It was thought that pressurisations in type III may obscure instances of normal peristalsis, the presence of which would alter the diagnosis.
Figure 1 (below): Type 1 Achalasia with normal IRP (22).
Major peristaltic disorders
It has been recognised that hypercontractility can include or be exclusive to the LOS and so this must be taken into consideration (6). Dr. Sweis noted that although this disorder does not generally disrupt function, it can be associated with pain and is not seen in health. V2.0 allowed a minor classification for hypertensive peristalsis with DCI>5000, however contractions of these magnitudes may be seen in normal patients and so it has been removed from v3.0. A DCI >8000 is uniformly associated to dysphagia or chest pain and was not seen in normal patients (Fig. 2), however the diagnosis now requires at least two swallows of the ten (7).
Absent peristalsis is still considered a major disorder but whereas in v2.0 this was recorded as a peristaltic segment in the 20mmHg isobaric contour of <3cm, it is now measured as a DCI of <100 (8).
In distal oesophageal spasm, peristaltic velocity is no longer a factor, and in fact rapid contraction has been removed as a peristaltic disorder. Spasm without premature latency may be due to variant achalasia and attention must be made to separate these (9).
Figure 2 (below) - Prevalence of hypercontractility in a population. (7)
Minor peristaltic disorders
As mentioned above measurement of length in the 20mmHg contour was previously preferred as a wider peristaltic gap was found to relate to incomplete transport (10). Now however, the term ineffective motility has returned requiring >50% of swallows to exhibit DCI<450. No distinction has been made between weak or failed resulting in the loss of ‘frequent failed peristalsis’ as a diagnosis. Dr. Sweis explains that ineffective motility is considered minor as it is most commonly associated with GORD rather than primary dysmotility and that it worsens with increased AET and symptoms (11).
The need for extra tests beyond the 5ml swallows has been a major criticism of the classification to date. Dr. Sweis agreed with studies that showed that 5ml swallows would rarely provoke symptoms (12) and are not representative of normal behaviour (13), however he rationalised the need for a reproducible standard. A survey he conducted showed that many departments were already doing more than the 5ml swallows and his explanation of how these tests function was interesting.
The multiple rapid swallow can involve either five 2ml swallows or a free drink of 200ml. The 10ml MRS should cause peristaltic inhibition followed by a post-inhibitory contraction revealing the state of neural reflexes in the oesophagus. Patients with a poor post-inhibitory response were shown to be more likely to develop dysphagia after anti-reflux surgery (14). In studies the 200ml MRS was able to reveal pathological resistance to flow (15) and it was especially useful in solidifying different achalasia subtypes (16).
Solid challenges, including viscous swallows or 1cc bread, can increase vigor, coordination and duration of swallows. Meal challenges have had slower uptake in clinical practice due to the increased study length and the complex patterns that occur. The presenter showed that in studies, meals frequently exhibit 2-3 pharyngeal contractions without a subsequent oesophageal contraction and that it is only when >5 consecutive swallows fail to produce a contraction that pathology should be considered (15). Meals can reproduce more symptoms, increase the yield of major motility disorders, and treatments based on the diagnoses give better symptom resolution (17).
Opinion and ideas for v4.0
The issue of tailoring anti-reflux surgery in relation to low DCI was raised during the lecture and although Dr. Sweis said that it was a future goal of the classification, so far studies had been unclear, however fundoplication was still performed in achalasia and so success may not be related to DCI.
V3.0 goes some way to addressing the problems some authors had with the classification of achalasia however issues with early or variant achalasia are likely to continue. It has been noted that although type II appears to be an earlier form of type I, that type III tends to occur in older patients, suggesting that it may be a different entity to achalasia (18). These question marks are likely to remain for the time being and the experience of the physiologist will be key in providing interpretation.
Disorders of the smooth muscle oesophagus and LOS have been the main concern so far and the current classification is robust in this sense. Calls have been made however for other areas to be included in the future (19) including disorders of the pharynx, conditions such as rumination and obstructions due to tight fundoplications or gastric bands. These areas of upper GI manometric investigations are certainly included in the repertoire of many physiologists yet are not covered by any agreed standards and until such time will suffer from inconsistencies between different centres.
Figure 3 (below) Correlation of impedance manometry and Barium swallow in bolus retention (21).
As a final note, the normative values in v3.0 are still based on swallowing in the supine position and Dr. Sweis repeated the contention of others that measurements in the supine position are unphysiological (13). This could be seen as an extension of the wider issue where conventional manometry is still in use. Studies have shown that HRM improves diagnosis and effort should be made to move away from the conventional line tracing (20). Inclusion of Impedance HRM is still seen as optional, however impedance manometry has been shown to correlate well with bolus retention as seen on Barium swallow (21), and provides additional information in an array of disorders.