Lower esophageal sphincter achalasia-like syndrome causing megaesophagus in a cat

Abstract

Case summary

Feline megaesophagus (ME) is a rare failure of esophageal motility leading to regurgitation, weight loss and sometimes death in cats. It has been identified secondarily to neurologic and neuromuscular disorders, mechanical obstruction of the esophagus (eg, vascular ring anomalies, esophageal stricture) and upper airway obstruction among others; when no cause is found, it is considered idiopathic. Videofluoroscopic swallow studies (VFSSs), especially using an unrestrained free-feeding protocol, are underutilized for comprehensive evaluation of cats with regurgitation, including identifying the etiology of ME. In this case report, a 3-month-old male intact domestic shorthair cat with a history of regurgitation since weaning and radiographic evidence of ME had VFSS features compatible with a functional obstruction of the lower esophageal sphincter (LES) consistent with LES achalasia-like syndrome. Medical management with sildenafil failed to improve clinical signs, and surgical correction of LES achalasia using a Heller myotomy and Dor fundoplication was declined. As a result of caregiver compassion fatigue from persistent regurgitation, euthanasia was elected.

Relevance and novel information

Videofluoroscopic documentation of functional obstruction of the LES (ie, LES achalasia-like syndrome) can identify a novel etiology of feline ME. Free-feeding unrestrained VFSS protocols are recommended to allow physiologic assessment of swallowing disorders with no higher risk of aspiration than eating and drinking at home. Recognition of LES achalasia-like syndrome may lead to further study of directed treatments targeting the functional obstruction as has been carried out in humans and dogs.

Case description

A 3-month-old male intact domestic shorthair cat was referred to the Veterinary Health Clinic, University of Missouri for further evaluation of congenital megaesophagus. The kitten had a history of regurgitation noted since weaning at 2 months of age and was notably smaller than the other two littermates. Regurgitation, initially thought to be vomiting, was noted on average three times daily, and appetite was described as ravenous. Generalized megaesophagus (ME) was diagnosed 1 month prior by the primary care veterinarian by thoracic radiography (Figure 1). Upright feedings of a commercial canned food (Fancy Feast Kitten Classic Pate; Purina) were given every 2 h by the owner during the day, which helped reduce the frequency but did not resolve the regurgitation. The kitten had received a series of three feline viral rhinotracheitis, calicivirus and panleukopenia (FVRCP) vaccines and had been administered pyrantel pamoate as a dewormer. Results for feline leukemia virus antigen, feline immunodeficiency virus antibody and heartworm antigen were all negative.

Figure 1

Thoracic radiography in a 2-month-old domestic shorthair cat. (a) Right lateral recumbent view showing ventral displacement of the trachea (black arrow) secondary to a severely distended esophagus. The esophagus is markedly dilated on its entire length, including the caudal portion (white arrows). The gas distended stomach (Sto) is in a normal position in the abdomen. (b) There is a distended esophagus (asterisk) and widening of the mediastinum (white arrows) causing rightward displacement of the trachea (Tr)

On physical examination, the kitten had a body weight of 1.09 kg with a body condition score (BCS) of 4/9, a muscle condition score of 2/3 and subjectively had stunted growth. The heart rate was lower than expected for an active kitten at 156 beats/min, but the remainder of the examination was unremarkable.

A free-feeding, unrestrained videofluoroscopic swallow study (VFSS) was performed to investigate for the presence of a functional obstruction of the lower esophageal sphincter (LES). The kitten was offered liquid, slurry and kibble with contrast as per the canine protocol. ¹ Results showed moderate gas dilation of the esophagus with a visible fluid line before feeding (Figure 2a). Oral preparatory and pharyngeal phases of deglutition were unremarkable for all consistencies. Esophageal swallowing was characterized by an absence of primary peristaltic waves with significant esophageal bolus accumulation. Ineffective secondary peristaltic waves were inconsistently produced in the distal third of the esophagus and failed to appropriately conduct the esophageal volume into the stomach. Small volumes passing from the esophagus into the stomach during swallowing demonstrated a classic ‘bird beak’ (Figure 2b). ² A larger volume of gastric filling was observed, independent of pharyngeal swallowing. During bolus passage, the LES was shown to dilate to a normal volume inconsistent with a mechanical obstruction, ruling out LES pseudoachalasia (Figure 2c). Liquid and slurry were the best tolerated consistencies.

Figure 2

Lateral still images from a videofluoroscopic swallow study (VFSS) performed on a 3-month-old male intact domestic shorthair cat. Cranial (left), caudal (right). (a) Baseline fluoroscopic image before feeding oral contrast material demonstrates esophageal dilation (dorsal and ventral esophageal borders, black arrows) and baseline fluid line (black arrowhead). A baseline fluid line is defined as fluid within the esophagus after a prolonged fast (⩾12 h) with lack of clearance. (b) Still image from the VFSS where the kitten is actively swallowing a bolus (puree consistency). The esophagus is markedly dilated with significant bolus accumulation forming a food column within the esophagus. A classic ‘bird-beak’ is observed where a narrowed column of contrast is seen passing through a narrowed lower esophageal sphincter (LES) (arrows) during pharyngeal swallowing (arrowhead). (c) Gastric filling without active swallowing. The LES (arrows) opens to an appropriate diameter not associated with pharyngeal swallowing.

Repeat thoracic radiography, in addition to showing generalized ME, revealed a focal alveolar lung pattern in the right cranial lung lobe, suspected to be secondary to aspiration. Because of a lack of respiratory clinical signs, absence of fever and lethargy, no therapy was prescribed to treat presumptive aspiration pneumonia. Instead, treatment focused on promoting gastric filling and minimizing retained esophageal ingesta. The Nutrition Service at the University of Missouri provided a nutrition plan. The kitten’s resting energy requirement (RER) was calculated as 54 kcal/day, with an initial daily goal of providing 3.0 x RER. To allow gradual acclimation to larger volumes of food, Recovery Ultra Soft Mousse in Sauce (Royal Canin) was blended to a smooth consistency without adding water and offered starting at 2.0 x RER and increasing to 3.0 x RER over 5 days. Meals were split into four feedings per day, with food placed on a slow feeder mat fixed to the hearth at a height to maintain a vertical position during feeding (Figure 3). It was recommended that the cat be held upright for an additional 5–10 mins after each meal.

Figure 3

Photograph demonstrating the at-home feeding protocol that incorporates upright feeding and a slow-feeder mat

To address the LES achalasia, sildenafil (2 mg/kg q8h) was prescribed, ³ with the intent to further increase the dose based on weight gain. A recheck was scheduled for 1 month later. At the subsequent recheck, the owner reported weight gain and continued ravenous appetite, but with no perceived change to frequency of regurgitation. The kitten’s body weight was 1.61 kg, with a BCS of 5/9 and muscle condition score of 3/3; however, overall, the kitten remained small for its age. Bradycardia at 120 beats/min was noted. A repeat VFSS, performed 1 h after administration of the morning dose of sildenafil, demonstrated mild improvement in LES relaxation during pharyngeal swallowing. However, the LES remained narrowed, with persistent esophageal bolus accumulation, likely reflecting the lack of observed clinical improvement. Vertical positioning for 5 mins and cine loop acquisition with the cat standing upright in the feeding kennel did not show chalasia of the LES (Figure 4). Surgical correction of the LES was discussed, but the owners chose to continue medical management while considering their options. Finally, euthanasia was performed at the primary care veterinary clinic shortly thereafter due to ongoing regurgitation and caregiver compassion fatigue.

Figure 4

Lateral still images from a videofluoroscopic swallow study performed on a 3-month-old male intact domestic shorthair cat after treatment with sildenafil. (a) Still images taken after consuming liquid and transitioning to puree consistency. Esophageal dilation is consistent with previous evaluations, including esophageal dilation and significant accumulation of food within the esophagus. (b) The food column persists despite being held upright for 5 mins before and during acquisition of the image, with the upper body out of the roof of the feeding kennel

Discussion

In this case, LES achalasia-like syndrome was diagnosed in a cat using an unrestrained, free-feeding VFSS protocol, documenting a functional obstruction at the LES, leading to the development of ME. Feline ME is rare and understudied, especially its etiology and targeted treatments. Reported causes of feline ME include myasthenia gravis, ⁴ dysautonomia,^5,6 vascular ring anomalies, ⁷ enteric ganglionitis, ⁸ muscular dystrophy,^9,10 esophageal stricture, ¹¹ upper airway obstruction,^12–14 diaphragmatic rupture, ¹⁵ lead toxicity ¹⁶ or idiopathic origins.^17,18 LES achalasia is thought to result from the loss of inhibitory neurons within the myenteric plexus of the distal esophagus and LES, leading to unopposed excitatory activity, subsequent failure of LES relaxation and ending in ME. ¹⁹ Given its dynamic nature, a definitive diagnosis of LES achalasia requires documentation of LES failure to relax during pharyngeal swallowing. In humans with dysphagia, tools such as endoscopy, barium esophagram and esophageal manometry are complementary and enable the diagnosis of LES achalasia. ¹⁹ In dogs, VFSSs have been shown to provide reliable features of LES achalasia-like syndrome and enable classification. ² High-resolution esophageal manometry remains primarily a research tool in veterinary medicine owing to its cost and limited availability. Its use has been predominantly in healthy dogs and its utility for diagnosis of LES achalasia-like syndrome in dogs or cats has yet to be established. ²⁰ Although congenital (LES) achalasia was first described in cats over 50 years ago,^21,22 no dynamic testing (ie, VFSS or esophageal manometry) was performed. Instead, gross descriptions, including ‘a tough fibrous band around the esophagus’ and the ‘cardia was constricted’ may more accurately reflect pseudoachalasia caused by a mechanical obstruction. ²²

Although VFSSs are considered the gold standard for diagnosing swallowing disorders in veterinary medicine, their application in cats remains limited. Traditionally, ME was diagnosed radiographically, and VFSS (typically performed with patients in lateral recumbency and fed or force-fed contrast material or food) was associated with a high risk of aspiration and limited value in determining etiology or assisting in the therapeutic management of ME. However, the use of unrestrained, free-feeding VFSS in dogs has completely changed the landscape of how swallowing disorders are diagnosed. This method has led to the identification of several aerodigestive conditions that bridge the respiratory and digestive systems.^23–25 Although the similarities between cats and dogs are understudied, there are important differences in VFSS interpretation between species.26

Diagnosis of LES achalasia-like syndrome in dogs has enabled novel targeted therapies aimed at relieving functional LES obstruction. These have been associated with a reduction in the frequency and severity of clinical signs and a decreased risk of life-threatening complications such as aspiration pneumonia.^27–30 Potential therapeutic options in dogs with LES achalasia-like syndrome include oral sildenafil, combination LES pneumatic balloon dilation, bougienage, local botulinum toxin injections and surgical correction via Heller myotomy and Dor fundoplication.^27–30 Of these, oral sildenafil, a phosphodiesterase 5 inhibitor, is the least invasive. Phosphodiesterase 5 inhibition promotes LES relaxation via nitric oxide. Nitric oxide serves as the primary mediator of the inhibitory ganglions in the myenteric plexus, which are lost in some forms of LES achalasia. ³ Paradoxically, as suspected in the cat described in this case report, LES relaxation can lead to gastroesophageal reflux (GER), which may manifest as persistent or worsening regurgitation and be misinterpreted as treatment failure. Although GER was not observed on the second VFSS, its dynamic and intermittent nature could have led to it being missed. In addition, sildenafil does not appear to be effective in all cases of LES achalasia (authors’ personal observation). Ballooning, bougienage and local botulinum toxin injections require general anesthesia, which is costly and associated with a high risk of aspiration due to ME. These techniques can also lead to GER. Surgical correction of LES achalasia-like syndrome also requires general anesthesia and is the most expensive treatment option (at least in the short term); however, because of the fundoplication creating an anti-reflux valve, it minimizes the chance of GER and is considered a permanent solution. Nevertheless, in all types of therapy, ME is expected to persist, with only minor improvements in esophageal motility reported postoperatively in dogs. ²⁹

General management principles for cats with ME include identifying and addressing underlying conditions, implementing tailored diets for smaller and more frequent feedings, and ensuring prandial and post-prandial vertical positioning. Recognition of LES achalasia-like syndrome in cats is required to investigate and assess the response to targeted therapy addressing the functional LES obstruction, which should improve ME management outcomes. As in dogs, the goals of treatment include reducing clinical signs (primarily regurgitation), supporting growth in kittens, maintaining appropriate body weight and muscle condition in adult cats, and minimizing complications such as aspiration-related respiratory disorders. Regardless of the chosen treatment, VFSSs are key in documenting efficacy and modifying dietary strategies. Serial VFSSs can be used to document which consistency (liquid, slurry or kibble) is best tolerated and to identify a constellation of other abnormalities. In the present case, the second VFSS performed in the kitten demonstrated that neither pharyngeal swallowing nor upright positioning enabled esophageal emptying or gastric filling, indicating a poor response to sildenafil, which was reflected in the persistent regurgitation. Although untested in this patient, surgical correction of the functional LES obstruction may have led to clinical benefits.

Conclusions

An unrestrained, free-feeding VFSS was useful in diagnosing LES achalasia-like syndrome as a cause of congenital ME in a kitten. Oral sildenafil failed to improve clinical signs or improve the functional LES obstruction, as confirmed on follow-up VFSS. Although surgical correction of LES achalasia was declined in this case, it should be considered in future patients.