Impaired Gastric Emptying in Primary Sjögren’s Syndrome

Study population

Twenty-eight patients with pSS (26 women, median age 62 yrs, range 29–65 yrs) according to the American-European Consensus Criteria¹⁶, from the outpatient clinic at the Department of Rheumatology at Skåne University Hospital, Malmö, Sweden, were included in the study. They were prospectively followed with regard to signs and symptoms of AD¹⁰.

Controls

The octanoate breath test controls consisted of 50 healthy controls recruited among laboratory staff, their relatives, and friends (25 women, median age 43 yrs, range 25–59 yrs). The control group for the deep-breathing test and orthostatic heart rate test consisted of 56 healthy individuals (22 women, median age 40 yrs, range 16–59 yrs), all of whom had passed a health examination without signs of cardiovascular disease, respiratory disorders, or diabetes mellitus¹⁷. The controls for the orthostatic blood pressure reaction test consisted of 238 healthy nondiabetic individuals (106 women, median age 60 yrs, range 16–96 yrs)¹⁸. The finger skin blood flow test controls were 80 healthy subjects (37 women, median age 43 yrs, range 19–81 yrs), all nonsmokers with no history of vascular disease, and were not taking any medication¹⁹.

Octanoate breath test

A standardized omelette was ingested after an overnight fast from 10 PM. The subjects were allowed to drink water until 1 hour before the test. During the test the subjects were in a seated position. The omelette contained 1 normal-size egg, 30 ml flour, 30 ml of 40% fat cream, salt, dill, and 100 μl octanoic acid (Euriso-top, Saint-Aubin, France). The yolk was separated from the white and the octanoic acid was injected into the yolk. The yolk was then baked separately in a microwave oven for 30 s. The egg white, flour, cream, salt, and dill were then added and the omelette was baked for another 2 min in the microwave oven. End-tidal breath samples were obtained before the meal and subsequently every 15 min for the next 4 hours. The test tubes used for breath samples were Labco Exetainer^® 12 ml (Labco Limited, High Wycombe, Buckinghamshire, UK). The tubes were then sent to the Department of Clinical Chemistry, Linköping University Hospital, for analysis. The half-time (t_half) and lag-time (t_lag) for gastric emptying were calculated as described in detail by Ghoos, et al²⁰, whose method was used for the test after slight modifications in accord with instructions from the laboratory where the analysis was conducted. The t_half is defined as the time from ingestion of a bolus until 50% of the bolus has been cleared from the stomach. The t_lag is the time from ingestion until the bolus is beginning to be cleared from the stomach. Because the t_half and t_lag were affected by age and sex, these variables were standardized accordingly and expressed as z-scores. Impaired gastric emptying (IGE) was defined as a z-score for t_half and/or t_lag ≥ 2 and gastroparesis as a z-score for t_half ≥ 2.

Laboratory tests

Blood samples were taken to assess signs of disease activity in pSS and included analyses of erythrocyte sedimentation rate (ESR), immunoglobulin G (IgG), and complements (C3 and C4). In addition, patients with pSS were tested for presence of rheumatoid factor (RF), antinuclear antibodies (ANA), anti-SSA antibodies, and anti-SSB antibodies. Thyroid-stimulating hormone (TSH), vitamin B12, and p-glucose were also assessed to rule out thyroid disease, B12 deficiency, and diabetes mellitus, respectively. All blood analyses were performed as routine analyses at the Departments of Clinical Chemistry and Immunology, Skåne University Hospital, Malmö and Lund.

Autonomic nerve function tests

The deep-breathing test was done after supine rest for 15 min. The heart rate was monitored by electrocardiogram (ECG) for 4 min and, once constant, 6 maximal expirations and inspirations were performed during a 1-min period. An expiration/inspiration (E/I) ratio was calculated as the mean of the longest R-R intervals during the expirations divided by the mean of the shortest R-R intervals during inspirations²¹. The E/I ratio mainly reflects parasympathetic nervous function^21,22.

For the orthostatic heart rate and blood pressure test, the subject was strapped on a tilt table, kept supine for 10 min, and then within 2 s tilted to an erect position, in which the subject remained for 8 min. ECG was used to monitor heart rate from 1 min before tilt. Systolic and diastolic blood pressures were measured before and every minute after tilt. A mean of the R-R intervals before tilt (A) and the shortest R-R interval after tilt (B) were determined from which an acceleration index, defined as (A − B)/(A × 100), was calculated^23,24. The systolic and the diastolic blood pressures before tilt (SBP_rest and DBP_rest) as well as the lowest systolic and diastolic blood pressures during the first 8 min after tilt (lSBP and lDBP) were determined. Orthostatic SBP and DBP ratios were then calculated: lSBP ratio=lSBP/lSBPrest and lDBP ratio=lDBP/DBPrest

For the finger skin blood flow test, the subject was seated in a semirecumbent position with the left hand on an aluminum holder, situated at heart level and with the middle finger placed in a groove of the holder. The temperature of the aluminum holder was kept stable at 40°C by a Peltier element. The finger skin blood flow was monitored using a laser Doppler imaging device, scanning an area of 2 × 2 cm of the distal phalanx of the third finger. The blood flow was then subsequently monitored every minute for 6 min during the heating procedure (h). The subject then immersed the contralateral hand and forearm into a water bath, kept at a stable temperature of 15°C, and kept it immersed for 3 min. A scan was performed every 30 s during immersion and afterward for another 3 min. Hence the finger skin blood flow of the left hand was monitored during the contralateral cooling procedure (c). By dividing the lowest finger skin blood flow value during the first minute of contralateral cooling (LDIc) by the mean of the last 2 measurements of finger skin blood flow at rest, before the cooling procedure (LDIh), a vasoconstriction (VAC) index could be calculated (VAC index = LDIc/LDIh). This has been shown to be a sensitive test for sympathetic nervous function in the skin¹⁹.

Because autonomic nervous function deteriorates with advancing age, the autonomic nervous function variables were age-corrected and expressed as z-scores by comparison with the 3 control groups. The z-scores were then compared to detect differences between patients with pSS and controls. Because sex does not seem to significantly affect autonomic variables measured in these tests^17,19, data were not matched for sex.

All tests were performed under standardized conditions and stable temperature and subjects were not allowed to eat or drink coffee or smoke prior to testing.

Questionnaire

The self-completed Autonomic Symptom Profile (ASP), assessing AD symptoms, was filled in during the octanoate breath test. The ASP evaluates presence and severity of AD symptoms in various AD domains. Its English original version has been validated in patients with AD of various etiologies²⁵ for subsequent use in patients with diabetes mellitus²⁶ as well as pSS²⁷. It has also been translated into Swedish and validated in patients with diabetes mellitus²⁸ and used in patients with pSS¹⁰. Further, the patients were assessed by a gastroenterologist for the presence of symptoms of IBS and FD, according to the Rome III criteria²⁹. The assessment was based on the answers from the ASP.

Statistical analyses

Because the t_half and t_lag were affected by age and sex, these variables were standardized using a linear regression model into which age and sex were added as covariates and the variables were expressed as z-scores. Z-scores ≥ 2 were considered pathological. Because of a skewed distribution of several variables, the Mann-Whitney U test and Fisher’s exact test were used for comparisons between groups and Spearman’s rank correlation test for correlations. Results are presented as median [interquartile range (IQR) limits] if not stated otherwise. P values < 0.05 were considered statistically significant.

The study was approved by the ethics committee at Lund University (LU563-2008). All participants gave written informed consent according to the Declaration of Helsinki.

Patient characteristics

None of the 28 patients examined had previously undergone any GI surgery. Six of the patients were taking medication known to affect autonomic nervous function (ß-blockers, n = 1, angiotensin-converting enzyme inhibitors 1, angiotensin II receptor blockers 1, calcium channel blockers 1, pilocarpine 2, diuretics 1), all of which were discontinued 24 hours prior to autonomic nervous function testing and the octanoate breath test. In addition, 2 patients were currently treated with selective serotonin reuptake inhibitors (SSRI), 1 patient with a combination of mirtazapin and pregabalin, 1 patient with prednisolone 5 mg/day, and 3 patients with hydroxychloroquine, none of which were discontinued. Twenty-one percent of the patients were current smokers. Patients were asked to refrain from smoking 24 hours prior to testing. All patients were nondiabetic and euthyroid. Further patient characteristics are presented in Table 1.

Octanoate breath test and clinical and laboratory associations

In patients with pSS, the age-standardized and sex-standardized t_half and t_lag were significantly prolonged in comparison to controls. Twenty-nine percent and 43% of patients with pSS had a pathologically prolonged t_half and t_lag, respectively, in comparison to controls (Table 2), and hence 29% and 43% presented signs of gastroparesis and IGE, respectively. If patients taking SSRI and pregabalin were excluded (medications that were not withheld and which could possibly interfere with gastric motility), the t_half and t_lag were still significantly prolonged in patients with pSS in comparison to controls (p = 0.02 and p = 0.00, respectively). Excluding patients taking medication withheld as well as those taking SSRI and pregabalin, the significant increase in t_lag remained (p = 0.02), while the increase in t_half became nonsignificant (p = 0.14). Excluding current smokers did not change the significant increase in t_half and t_lag (p = 0.02 and p = 0.01, respectively). Although 82% of patients reported various nonexocrine symptoms (Table 1), the presence of these was not associated with signs of IGE (data not shown).

Correlating t_half and t_lag with inflammatory measurements (ESR, IgG, C3 and C4), t_lag was found to correlate significantly with both ESR (r_s = 0.51; p = 0.01) and IgG (r_s = 0.43; p = 0.02). In accordance, the ESR and IgG were found to be significantly increased in patients with abnormal t_lag in comparison with patients with normal t_lag [median IQR 24 (17–34) vs 9 (7–16), p = 0.03; and 19.6 (14.1–30.8) vs 15.2 (10.9–18.8), p = 0.03, respectively].

Moreover, comparing RF-seropositive with RF-seronegative patients, the former were found to have significantly prolonged t_half and t_lag. In addition, ANA-seropositive patients showed a nonsignificant tendency toward a prolonged t_half and t_lag in comparison to ANA-seronegative patients (Table 3).

Octanoate breath test and autonomic nervous function

Patients with pSS were found to have a significantly decreased E/I ratio as well as significantly decreased ratios of lSBP and lDBP in comparison to controls, indicating both parasympathetic and sympathetic dysfunction. Further, patients reported significantly more AD symptoms in comparison to controls, mirrored by significantly increased ASP domain scores as well as an increased ASP total score (Table 4).

However, correlating t_half and t_lag to the ART and ASP variables, only the lDBP ratio was found to be significantly correlated with t_lag (r_s = −0.47; p = 0.01). Of note, symptoms of gastroparesis were not significantly associated with the t_half or t_lag (data not shown).

Octanoate breath test and functional bowel symptoms

Thirteen patients (46%) were found to have IBS and 25 (89%) patients to have FD according to the Rome III criteria²⁹. However, no significant associations between presence of symptoms of IBS or FD and signs of IGE were found (data not shown).