In the DBPCFC-positive group, the only presenting symptom reported significantly often as leading to the suspicion of CMPA was loose stools, in 14 of 18 (78%) children (Table 3). Loose stools were reported during the active CM challenge in all of them. During the placebo challenge, loose stools were reported only for 1 patient in the positive challenge group (with lower stool frequency than during the active challenge), whereas in the challenge-negative group during placebo, loose stools were reported for 10 of 39 (25%) children. Vomiting/spitting up occurred with similar rates in the challenge-negative group during placebo (7/39, 18%), and in the challenge-positive group during active challenge (3/18, 17%). The hypoallergenic formula used during the elimination period did not affect the outcome of the DBPCFC. The referring doctor had started an amino acid formula for a CM-elimination diet for 11 (19%) children; 3 of them reacted to the active challenge, the same proportion as in the entire cohort. Eight children were receiving soy-based formula and 4 of them reacted to the active challenge.
We performed adult-type hypolactasia genotyping in 52 patients. In Finland, the prevalence of the adult-type hypolactasia CC genotype (which is associated with low lactase levels) is 18% (17). In the DBPCFC-negative group (35 analyses), 11 (34%) patients had the CC genotype. This difference in population frequency is significant (P = 0.038). In the DBPCFC-positive group, the CC genotype was present in 4 of 17 (24%) patients (Table 2).
The DBPCFC protocol that we used was feasible and safe. The observed symptoms were milder than expected. Only 1 child reacted by vomiting within 30 minutes of the provocation (on placebo); there were no other immediate reactions among the studied children. Reactions to CMP occurred within 48 hours, except in 1 patient in whom symptoms were reported after 6 days (on active challenge).
Significant placebo reactions occurred in 18 of 39 (46%) patients with negative DBPCFC, all within 48 hours (Table 3). The placebo reactions were unpredictable: The reactions could be directly attributed to concurrent infection in only 3 patients. The most common placebo symptoms in the challenge-negative group were increased irritability or crying/fussiness (15 patients), vomiting (7 patients), and loose stools (10 patients). Upper respiratory symptoms were reported during both the placebo and the active challenges, but parents seldom associated them with concurrent GI symptoms.
Reintroduction of CMP to the diet after negative challenge was mainly successful. Thirty-seven (95%) of the DBPCFC-negative patients used CMP-containing dairy products, even though at the 6-month follow-up some of them still refused to drink CM as such. The 2 patients who had not been given CMP by 6 months time tolerated CMP when encouraged to try it right after the follow-up appointment. Feeding-related problems (refusal to eat, vomiting/gagging, other diet restrictions without food allergy diagnosis) persisted after the negative challenge result in 6 patients (15%), and also in 6 patients (33%) in the challenge-positive group. In the DBPCFC-positive group, 12 of 18 patients had not been given any CMP by the 6-month follow-up, despite exhibiting mild symptoms during the challenge. The 6 challenge-positive patients who were given small amounts of CMP tolerated it well. Symptoms did not persist in patients who were taking extensively hydrolyzed formula, and thus we did not need to start any of these patients on an amino acid formula after the challenge.
To the best of our knowledge, this study is the largest published study on a prospective cohort of patients with suspected GI manifestations of CMPA only. Vanto et al (18) reported on 301 children suspected of having CMPA who underwent a 5-day DBPCFC, with 34% of the patients manifesting GI symptoms. Unfortunately, they did not report the outcome of the DBPCFC for the GI-manifested group alone. We performed the 5-day DBPCFC in 57 infants. The proportion of positive active challenge reactions noted in our study was 32%, the same range as in other previous studies using the DBPCFC (19,20). Based on our clinical experience, the study patients were representative of present-day CMPA suspicions in a Finnish allergy clinic. On average, the time frame from the beginning of the symptoms to the DBPCFC was relatively short, with a median duration of cow's-milk–free diet of 2.5 months. It may be argued that natural tolerance had developed during this time. The median age of our patients was 8.7 months; tolerance to CM has been shown to develop in the majority of patients with CMPA only after the age of 1 year (30). In fact, the 2 patients with the longest durations of CM-free diet were DBPCFC positive. Although the nature and severity of symptoms with these infants do not match those described usually with food allergy–linked gastroenteropathies, the parents believed that the problem was significant enough that they agreed to the time-consuming and demanding protocol of the DBPCFC. Therefore, mild forms of the disease do not explain the large number of suspected cases with CMPA that were later rejected. Considering the frequency and nature of the placebo reactions (eg, reported loose stools in 25% on placebo), it is likely that some of the DBPCFC-positive reactions we observed may in fact be false. This also is in accordance with previous reports (19,20).
The pathology behind non–IgE-mediated GI manifestations of CMPA remains elusive. The universally used theory involves T-cell–mediated immunological responses (21). The paucity of confirmative data may be because of the fact that previous studies have either not been done among prospectively recruited, DBPCFC-confirmed patients or that they have pooled together both IgE-mediated and non-IgE CMPA as well as possible placebo reactions. In our study, in both the DBPCFC-negative and -positive groups, SPTs for CM were positive (wheal size 3–4 mm) in 2 children with no associated skin manifestations. Regarding the SPT wheal size in CMA in children, the 95% positive decision point corresponds with wheal size 12.8 mm; for wheal size 3 to 4 mm, the predictive probability is estimated just <50% (22). FPIES is the most severe GI-related manifestation of CMPA (8). The symptoms of FPIES manifest within a few hours with severe repetitive vomiting and lethargy, followed by diarrhea. None of our patients presented with FPIES-like symptoms. Our clinical suspicion is that this more severe form of non–IgE-mediated CMPA has in fact become rare; the reasons for this remain speculative.
The GI symptoms that parents in this study associated with suspicion of CMPA were grouped in the following way: crying/fussiness, loose stools, vomiting/spitting up, flatulence, and constipation. Parental perception of “excessive” crying or fussiness during infancy is extremely subjective (3), and the other described symptoms also overlap considerably with normal infant GI physiology. We prospectively collected detailed symptom data on charts both 1 week before and during the provocations. Only the parental report on “loose stools,” which we use here to denote stools that parents perceived as liquid with increased frequency, applied significantly more often to the DBPCFC-positive group compared with the DPCFC-negative group. Because loose stools were in fact reported in 25% of the DBPCFC-negative group during placebo challenge, even this symptom cannot be reliably interpreted in open challenges. Rectal bleeding has been associated with CMPA, but none of our patients presented with hematochezia, in accordance with other reports (23,24). Constipation in an infant may be worsened by abundant CMP, but the immunological (or allergic) nature of this phenomenon is unproven (1). In our cohort, the 5-day CMP challenge did not provoke constipation. Failure to thrive in the few patients in our cohort was in fact associated with dietary restrictions and feeding problems, rather than with persisting CMPA symptoms.
Placebo reactions were so remarkable in nearly 50% of challenge-negative children that the parents identified the placebo milk period as the more symptomatic. We observed similar rates for vomiting/spitting up occurring during placebo challenge in the DBPCFC-negative group and during active challenge in the DBPCFC-positive group. Thus, care should be taken if relying on vomiting/spitting up only as a CMPA symptom. Also excessive crying/fussiness as perceived and reported by parents did not agree with DBPCFC results, in concordance with a previous study (9). Our results clearly show that in gastrointestinally manifested CMPA suspicion, open food challenges should not be used.
The use of an amino acid formula was frequent (19%) in our cohort, possibly reflecting the diagnostic challenges in gastrointestinally manifested CMPA. In a randomized prospective trial, DBPCFC-proven allergy to extensively hydrolyzed formula occurred in 2.2% of CMPA patients, 69% of whom were negative for CM-specific IgE (25). In the present study, the use of amino acid formula did not raise the likelihood of a positive DBPCFC reaction. In the challenge-positive group, none of the patients on extensively hydrolyzed formula had persisting symptoms. It should be noted that most extensively hydrolyzed hypoallergenic formulas contain lactose, whereas the only amino acid formula available in Finland is lactose-free. Our challenge protocol was not designed to test lactose intolerance.
The more frequent adult-type hypolactasia CC13910 genotype in children with GI symptoms suspected of CMPA deserves attention. Because of the study size, this finding may relate to a low number of patients; however, in adults, the CC13910 genotype frequency was higher than expected in those experiencing unexplained GI pain, even when controlled for CM consumption (26). The lactase activity levels in CC genotype children are individual, but they start to decline after preschool age in the majority of white children (27). Thus, a low level of lactase related to the genetic trait is unlikely, although not excluded, in our patients. Interestingly, in colicky infants, abnormal breath hydrogen testing may occur, indicating possible carbohydrate malabsorption in such patients (28). The mechanisms for regulation of lactase enzyme activity levels in infants and the presentation of intestinal symptoms in children with CC13910 allele are incompletely understood (29).
The strengths of this study include its prospective setup, its detailed challenge, and follow-up data. Our clinic is a secondary referral center for pediatric outpatients within an urban area with a population of >1 million. In our clinic, the DBPCFC is in routine use, especially in non-IgE CMPA. Thus, those who refused to participate did so because of the laboratory tests involved in the study or because of the study DBPCFC schedules. One pediatrician and nurse supervised all of the study DBPCFCs, which adds significantly to the consistency of the results. The nearly 100% rate of infants using CMP without symptoms after negative DBPCFC confirms the negative challenge results.
The limitations of this study include its size and the DBPCFC protocol. The 5-day duration of the DBPCFC was designed to provoke the delayed reactions that occur within 72 hours of ingestion. The eventual percentage of positive active challenges was lower than we expected. Therefore, the power of this study to recognize the subtypes of CMP intolerance (inflammatory/allergic, lactose-associated, functional or false-positive) is not sufficient. We did not search for proof of possible concurrent microbial infections which could cause symptoms similar to CMP-provoked GI symptoms. We did not believe it was prudent to re-perform the DBPCFC in the CMPA-positive group, because of preexisting feeding problems and parental opposition. Because the symptoms noted during the challenge were relatively mild, we instructed the parents to perform re-challenges at home after 3 months; however, this was done infrequently, even though we always discussed with the parents the possibility of false-positive challenges.
In conclusion, we have reported findings for a cohort of 57 patients undergoing DBPCFC for suspicion of GI-manifested CMPA. The diagnosis was confirmed in only one-third of the patients; CM-specific IgE was negative in all. Placebo reactions were common and can easily lead to biased interpretation in an open challenge. In terms of the suspicion of CMPA with GI symptoms, a trial of extensively hydrolyzed formula is reasonable; but also other causes for the GI symptoms should be identified. Further studies are needed to assess the association of suspected GI symptoms with the adult-type hypolactasia CC genotype.
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Keywords:© 2013 by European Society for Pediatric Gastroenterology, Hepatology, and Nutrition and North American Society for Pediatric Gastroenterology,
adult-type hypolactasia; cow's-milk allergy; double-blind placebo-controlled food challenge