The use of wireless motility capsule in the diagnosis and monitoring of gastroparesis

Background

Gastroparesis is a chronic disorder characterized by delayed gastric emptying in the absence of mechanical obstruction, which results in typical symptoms of nausea, vomiting, bloating, abdominal distention, postprandial fullness, early satiation, and upper abdominal pain . Population-based studies have estimated the age-adjusted incidence rate of gastroparesis to be 2.4 patients per 100,000 person-years for men and 9.8 patients per 100,000 person-years for women, while prevalence was estimated to be 9.6 per 100,000 men and 37.8 patients per 100,000 females . However, these studies may be significantly underestimating the true prevalence of gastroparesis. One study reported 1.8% of the general population exhibited typical symptoms of gastroparesis but only 0.2% of patients were formally diagnosed . This may relate to lack of awareness of this condition, confusion about available methods for diagnosis of gastroparesis, and significant overlap between gastroparesis and related conditions, particularly functional dyspepsia.

Impaired gastric accommodation

Upon meal ingestion, the gastric fundus undergoes a physiologic reflex called gastric accommodation mediated by nitrergic pathways, which results in increased volume of the gastric fundus without accompanying rise in intragastric pressure . Impaired gastric accommodation has been identified in up to 43% of patients with gastroparesis and correlated with symptoms of early satiation and weight loss .

Gastric neuromuscular dysfunction

Once the food bolus passes into the distal stomach, solid food is ground into small particles, in a process called trituration, by a combination of stomach acid and high-amplitude antral contractions . Antral contractions are mediated by extrinsic vagal innervation and intrinsic cholinergic neurons. Gastric emptying occurs when the food particles are 1–2 mm in size . Disruption in nitrergic neuronal pathways, including neuronal nitric oxide synthase (nNOS) immunoreactive cells in the gastric myenteric plexus , is postulated to be an important pathophysiologic mechanism in gastroparesis and may result in pyloric sphincter dysfunction or pylorospasm . As nitric oxide acts as an important survival factor the interstitial cells of Cajal , loss of these pacemaker cells in the gastrointestinal tract may result in antral hypomotility . These abnormalities in neuromuscular function may subsequently result in delayed gastric emptying.

Visceral hypersensitivity

Abdominal pain is a frequent symptom and reported by up to 90% of gastroparesis patients with up to 34% reporting severe or very severe pain . However, abdominal pain correlates poorly with gastric emptying of solids or liquids. Prior studies suggest abdominal pain may be related to visceral hypersensitivity to gastric distention . Patients with abdominal pain also demonstrated loss of S100 neural fibers in the gastric muscularis propria and altered central nervous system processing of pain signals .

Gastric emptying scintigraphy

Diagnosis of gastroparesis entails demonstrating objective evidence of delayed gastric emptying and exclusion of mechanical obstruction. Gastric emptying scintigraphy (GES) is the most common method for diagnosis of gastroparesis. Normative data with GES using a low-fat meal in healthy volunteers has been published with >60% retention of the test meal at 2 hours and >10% retention at 4 hours considered as abnormal .

GES has several advantages, including its wide availability, ability to measure emptying of both solid and liquid test meals as well as measures of gastric accommodation . However, despite consensus recommendations from the American Neurogastroenterology and Motility Society and the Society of Nuclear Medicine , the main limitation of GES remains the lack of standardization across different centers. There is also considerable intra-individual variation in gastric emptying rates with coefficients of variation of up to 24% . Furthermore, prior studies have reported poor correlation between gastric emptying rates and symptoms , which raises the question of whether gastric motility testing is required or even clinically useful for the diagnosis of gastroparesis . However, the latter two limitations are not unique to GES and apply to other tests of gastric transit as well, including wireless motility capsule.