Lymphocyte Stimulation Test and Oral Food Challenge in the Diagnosis of Food Protein–Induced Enterocolitis Syndrome Due to Short‐Neck Clam

ABSTRACT

Clam‐induced food protein–induced enterocolitis syndrome (FPIES) is rare in children, and lymphocyte stimulation testing (LST) may be useful for diagnosis. Symptoms were induced at lower doses than typical oral food challenge (OFC) doses, suggesting the possibility of reducing the testing burden for pediatric patients.

1. Introduction

Food protein‐induced enterocolitis syndrome (FPIES) is a subtype of non‐immunoglobulin E (IgE)‐mediated gastrointestinal food allergy, characterized by vomiting after ingestion of the trigger food, typically in the absence of food‐specific IgE [1, 2]. Shellfish, including short‐neck clam, are reported to account for approximately 3.7% of all FPIES trigger foods [3]. Although short‐neck clams are widely consumed worldwide, reports of short‐neck clam‐induced FPIES remain limited, and diagnostic methods other than oral food challenge (OFC) have not been established. The lymphocyte stimulation test (LST) measures the proliferative response of lymphocytes to a causative antigen and may be useful in the diagnosis of delayed allergic reactions, including FPIES triggered by food ingestion [4, 5]. However, the utility of LST in short‐neck clam‐induced FPIES remains unclear. Here, we report a case of short‐neck clam‐induced FPIES in which a low‐dose OFC was performed following a positive LST result, leading to the diagnosis. We also discuss the LST findings and the OFC dose used for the diagnosis of short‐neck clam‐induced FPIES.

2. Case Report

2.1. Case History/Examination

A 6‐year‐old girl presented to our hospital after three episodes of vomiting that began 3 h after she had eaten heated short‐neck clam in paella earlier that day. She had no known allergies to other foods, including mollusks such as squid and octopus or crustaceans such as shrimp and crab. She had no history of bronchial asthma or atopic dermatitis, although a family history of allergic rhinitis was noted. Physical examination was unremarkable, with no rash or other significant findings.

2.2. Investigations

Laboratory testing showed a total IgE level of 178 IU/mL. Specific IgE antibodies to short‐neck clam, scallop, purple sea urchin, and oyster were all below 0.10 kUA/L (Thermo Fisher Scientific, Waltham, MA, USA). The white blood cell count was 5500/μL, with 39% neutrophils and 2.7% eosinophils, and the thymus and activation‐regulated chemokine level was 477 pg/mL.

The lymphocyte stimulation test (LST) was performed by a commercial laboratory (BML Inc., Tokyo, Japan) and showed a stimulation index of 2.8 relative to the negative control (phytohemagglutinin‐stimulated culture, 161,596 cpm; negative control, 186 cpm; heated whole short‐neck clam, 514 cpm). For antigen preparation, the clams were microwaved at 600 W for 1 min until the shells had fully opened, after which the broth was discarded and only the edible portion was used. In Japan, a stimulation index of 1.8 or higher relative to the negative control is commonly used as the practical cutoff for a positive LST result; accordingly, this threshold was adopted in the present case.

Three weeks later, an open‐label oral food challenge (OFC) was performed using 5 g of heated short‐neck clam meat. Based on the patient's body weight of 20 kg and the protein content of short‐neck clam, this corresponded to an estimated protein dose of 0.015 g/kg. The clam was prepared as described for the LST, and only the edible portion was used after the broth had been removed. The patient developed vomiting 4 h after ingestion, followed by two additional episodes within the next hour. She also developed pallor and decreased activity, but no cutaneous or respiratory symptoms suggestive of an IgE‐mediated reaction were observed. Because she had repetitive vomiting 3–4 h after ingestion, along with pallor and decreased activity, in the absence of IgE‐mediated symptoms, she was diagnosed with acute food protein‐induced enterocolitis syndrome (FPIES) due to short‐neck clam in accordance with the international consensus guidelines.

Her condition improved with hydration and rest after vomiting. She had no fever or other abnormal findings on the following day. Blood tests were not performed before or after the OFC because parental consent was not obtained. Thereafter, short‐neck clam was eliminated from her diet, and no recurrence was observed during 1 year of follow‐up. The patient did not wish to consume short‐neck clam again, and a repeat OFC is not planned.

3. Discussion

In this report, we examined the lymphocyte proliferative response on LST and the OFC dose for short‐neck clam. Previous reports have also described the use of LST for short‐neck clam, but the methods used to prepare the clam differed among studies. Murai et al. used the whole raw clam, whereas Masumi et al. used the whole heated clam [4, 5]. In Japan, short‐neck clams are generally eaten after cooking; therefore, we used only the edible portion of heated clam in our test and obtained a positive result. Although it remains unclear which preparation method is more appropriate for testing, our findings suggest that the proteins responsible for triggering allergic reactions in the patient's gastrointestinal tract may be heat‐stable components.

LST has been used to evaluate non‐IgE‐mediated food allergies, including FPIES; however, the methodology has not been standardized, and the interpretation of the results remains controversial. In a previous report, Masumi et al. found that LST was also positive in healthy controls [4], indicating that false‐positive results should be considered. In addition, healthy controls were not included in the present case, and the positive cutoff value for LST has not been clearly established, which are important limitations. In FPIES, LST should therefore be regarded only as an adjunctive diagnostic test, and the definitive diagnosis should rely on OFC.

Regarding the challenge dose used in OFC, standard diagnostic protocols recommend a protein dose of 0.06–0.6 g/kg, with a maximum of 3 g of total protein or 10 g of total food [1]. In previous reports, challenge doses of 16–60 g of heated short‐neck clam were used. Assuming that 100 g of short‐neck clam contains 6 g of protein, this corresponds to 0.96–3.6 g of clam protein. Because patient body weights were not reported in those studies, we estimated the protein dose per kilogram using the ideal body weight for each age, which yielded an approximate clam protein dose of 0.05–0.17 g/kg. Assuming that the edible portion of one clam weighs 5 g, this would correspond to approximately 3–12 clams [4, 5]. In the present case, because the patient disliked short‐neck clam, we performed the OFC using a lower dose (clam protein dose, 0.015 g/kg), which still produced a positive result. As short‐neck clam contains relatively little protein for its total weight, calculating the challenge dose on a body weight basis according to standard guidelines may result in particularly large food amounts in older children. This case suggests that symptoms may be provoked even by a smaller amount than the generally used doses reported previously, which may help reduce the burden and risk associated with OFC. Further studies are needed to determine the optimal challenge dose.

Finally, this patient had never consumed other shellfish, such as freshwater clams or scallops, because of food preference. At present, we plan to continue eliminating all shellfish from the diet. The clinical cross‐reactivity among shellfish has not yet been sufficiently clarified, and further accumulation of cases is warranted.

4. Conclusion

Although clam‐induced FPIES is rare, LST may serve as a potential diagnostic aid, comparable to its application with other foods associated with FPIES. In addition, positive results may occur at challenge amounts lower than those typically used for diagnosing general FPIES.

Author Contributions

Sayuri Kajitani: data curation, writing – original draft, writing – review and editing. Manabu Miyamoto: conceptualization, data curation, formal analysis, writing – review and editing. Shigemi Yoshihara: supervision.

Funding

The authors have nothing to report.

Ethics Statement

Ethics Committee approval is not required for a single case report at our institution.

Consent

In accordance with Clinical Case Reports' patient consent policy, written informed consent for publication of the clinical details and any accompanying images was obtained from the patient (or their legal guardians, where applicable) prior to submission. Identifying information has been omitted to protect patient privacy. The signed consent forms are held by the corresponding author and will be provided to the journal upon request.

Conflicts of Interest

The authors declare no conflicts of interest.

Data Availability Statement

This study is a single pediatric case report. Due to considerations of patient privacy and ethical concerns, the data are not publicly available. The data cannot be shared to ensure the protection of patient confidentiality.