Retrograde cricopharyngeus dysfunction (R-CPD; also known as the inability to belch syndrome) is a medical condition first identified by gastroenterologist, Dr Peter Kahrilas, in 1987.^[1] However, the condition only began to receive more attention following a 2019 report by ENT surgeon, Dr Robert Bastian, which described a very high rate of symptomatic relief from injection of botulinum toxin into the cricopharyngeus muscle.^[2] Uniquely, awareness of the condition has spread predominantly through patients themselves rather than the medical community via numerous social media forums.^[3][4] Awareness of the condition amongst primary care physicians and specialists remains low and patients report needing to seek out specialists who are familiar with and can treat the condition through online research.^[5][6]

The condition is characterised by chronic gastrointestinal symptoms relating to excessive gas retention including abdominal bloating with distension, flatulence, audible gurgling sounds, and chest and abdominal discomfort.^[2] Some with the condition are also unable to vomit, or can only do so with great difficulty. In most cases, inability to belch is a lifelong problem.^[7] R-CPD has a significant detrimental impact on patients' quality of life.^[6][8]

The cricopharyngeus muscle is the major muscle comprising the upper esophageal sphincter (UES). It is a strap-like, C-shaped muscle at the base of the throat, behind the larynx. The UES encircles the proximal (upper) opening of the oesophagus.^[9] The upper esophageal sphincter has a residual tone which is in fact augmented as it is stretched open.^[10]

Swallowing of air during eating and drinking is normal. However, as the air cannot be absorbed by the gastrointestinal tract, it is mostly vented via burping. A transient relaxation of the lower esophageal sphincter allows swallowed air in the stomach to rise into the esophagus where it triggers a reflex relaxation and opening of the UES. In R-CPD, all steps of this 'belch reflex' occur normally up until the last one; despite gaseous distension of the esophagus, the UES fails to open. It is believed that all the symptoms of R-CPD occur due to failed expulsion of swallowed air, and thereby buildup of gas throughout the entire gastrointestinal tract.^[11]

Many patients have R-CPD suffered from years of delayed diagnosis and misdiagnosis, and unsuccessful empiric treatment of gastrointestinal disorders including GERD, aerophagia, gallbladder dysfunction, and IBS.^[6] Patients with R-CPD often undergo a battery of tests including nasendoscopy, gastrointestinal endoscopy, and barium swallow, which are almost always unrevealing.

In cases where symptoms are classical of R-CPD, many experienced specialists have treated the condition without formal diagnostic testing. However, physicians from the Netherlands and Australia have validated a specific diagnostic protocol using esophageal high-resolution manometry which is highly accurate in obtaining a conclusive diagnosis of R-CPD.^[12][7]

The treatment of choice is injection of Botulinum toxin into the cricopharyngeus muscle.^[2] The effect of Botulinum toxin is to temporarily weaken or paralyze the muscle. Reported success rates for inducing the ability to belch are extremely high, ranging from 88-92%.^[13] The effect of botox is delayed for three days on average and most patients with successful results report the ability to burp by the fifth day after the procedure. For most, the effect will last beyond the first three to six months of direct Botox effect and is most frequently a lifelong cure.^[13] A small percentage of patients will require a subsequent injection of Botox for lasting results.^[14] An alternative if the injection is unsuccessful is to undergo partial cricopharyngeal myotomy.^[15]

Presently, there are three described methods by which cricopharyngeal Botox injection can be performed:

1. The most commonly performed approach is injection via direct (rigid) laryngoscope, under general anesthesia. This is the technique favored by most ENT surgeons.
2. An injection technique via flexible gastrointestinal endoscopy was pioneered by Australian gastroenterologist Dr Santosh Sanagapalli. This technique appears to have equivalent high success rates,^[7] while having potential advantages given it avoids the risks associated with rigid scopes and general anesthesia.
3. Injection can also be performed by a percutaneous (directly through the skin) approach. While success rates are markedly lower, percutaneous injection has the advantage of being able to be performed as an in-office procedure under local anaesthetic.^[16]

Being related to the temporary effect of the Botulinum toxin, side effects are also temporary and typically resolve without treatment. The most common side effect is difficulty swallowing which often requires temporary diet modification and altered eating style. Less common side effects include sore throat, difficulty breathing on exertion, voice change and reflux/regurgitation. Side effects appear to be similar no matter which injection technique is used.