Occult constipation masking as irritable bowel syndrome with predominant diarrhea in Bangladeshi children

Abstract

BACKGROUND

Occult constipation (OC) is defined by the absence of classical symptoms of constipation on initial clinical history, despite objective evidence of fecal retention, such as the presence of hard stool on digital rectal examination or fecal impaction identified on plain abdominal radiography. It is frequently undiagnosed in children and presents with a diverse array of symptoms, such as abdominal pain and frequent defecation with mucoid feces. These symptoms are strikingly similar to irritable bowel syndrome (IBS) with diarrhea (IBS-D).

AIM

To verify the hypothesis that OC may present with the features of IBS-D.

METHODS

This is a prospective observational study that involves consecutive children who were referred to our center as primarily diagnosed with IBS-D (consistent with Rome IV criteria) by another physician and did not improve after at least three months of treatment. Patients presenting with red-flag symptoms suggestive of organic disease were excluded from the study. Patients who exhibited fecal impaction on a plain abdominal radiograph were diagnosed as OC and were administered magnesium hydroxide (milk of magnesia; 400 mg/5 mL) for a period of two months, with a progressive taper over the course of one month. Outcomes were assessed based on changes in pain intensity, frequency, and stool characteristics after the commencement of treatment.

RESULTS

This study included 54 patients who were diagnosed with IBS-D by other consultants and were unresponsive to treatment. Of these patients, 49 (91%) had OC mimicking IBS-D. After commencing treatment for OC, 46 (94%) of the 49 patients demonstrated a positive clinical response (44 good, 2 satisfactory).

CONCLUSION

Children presenting with IBS-D related symptoms who are unresponsive to standard therapy may benefit from evaluation for OC before considering escalation to more invasive investigations.

Key Words: Irritable bowel syndrome; Functional gastrointestinal disorders; Abdominal pain; Diarrhea; Occult constipation

Core Tip: Occult constipation (OC) is a significant diagnostic challenge because its symptoms, such as abdominal pain and frequent mucoid stools, often mimic those of irritable bowel syndrome with diarrhea. This clinical overlap frequently leads to misdiagnosis, where patients receive treatments that inadvertently worsen the underlying fecal impaction. Utilizing a plain abdominal X-ray serves as a practical and effective tool to visualize fecal loading and confirm the diagnosis of OC.

INTRODUCTION

In our day-to-day practice, functional gastrointestinal disorders (FGIDs) are common in the pediatric population. FGIDs mean symptoms attributable to the gastrointestinal tract that are not related to structural or biochemical abnormalities and are diagnosed on the basis of the Rome criteria[1,2]. Irritable bowel syndrome (IBS) is a common FGID in the pediatric age group, with a prevalence of 2.8% (United States of America) to 22.6% (Türkiye). In Asian children, the prevalence is 12.4%[3]. The diagnosis of IBS is symptom-based and is performed according to the Rome criteria, and recently the Rome IV criteria were published (Table 1)[2,4].

Table 1 Rome IV criteria for the diagnosis of functional constipation and irritable bowel syndrome.

Diagnostic criteria for functional constipation

Must include 2 or more of the following occurring at least once per week for a minimum of 1 month with insufficient criteria for a diagnosis of irritable bowel syndrome:

2 or fewer defecations in the toilet per week in a child of a developmental age of at least 4 years

At least 1 episode of fecal incontinence per week

History of retentive posturing or excessive volitional stool retention

History of painful or hard bowel movements

Presence of a large fecal mass in the rectum

History of large diameter stools that can obstruct the toilet

In addition, the symptoms are insufficient to fulfill the diagnostic criteria of irritable bowel syndrome.

Diagnostic criteria1 for IBS

Must include all of the following:

1 Abdominal pain at least 4 days per month associated with one or more of the following:

Related to defecation

A change in frequency of stool

A change in form (appearance) of stool

2 In children with constipation, the pain does not resolve with resolution of the constipation (children in whom the pain resolves have functional constipation, not irritable bowel syndrome)

3 After appropriate evaluation, the symptoms cannot be fully explained by another medical condition

1Criteria fulfilled for at least 2 months before diagnosis

Diagnostic criteria for IBS subtypes

IBS with predominant constipation

More than one-fourth (25%) of bowel movements with Bristol stool form types 1 or 2 and less than one fourth (25%) if bowel movements with Bristol stool form types 6 or 7

IBS with predominant diarrhea

More than one-fourth (25%) of bowel movements with Bristol stool form types 6 or 7 and less than one fourth (25%) if bowel movements with Bristol stool form types 1 or 2

IBS with mixed bowel habits

More than one-fourth (25%) of bowel movements with Bristol stool form types 1 or 2 and more than one fourth (25%) of bowel movements with Bristol stool form types 6 or 7

IBS unclassified

Patients who meet diagnostic criteria for IBS but whose bowel habits cannot be accurately categorized into 1 of the 3 groups above

¹Diagnostic criteria for irritable bowel syndrome.

IBS: Irritable bowel syndrome.

IBS is a disorder of the brain gut axis involving altered interactions between the central and peripheral nervous systems, leading to visceral hypersensitivity. However, not all cases are explained by central mechanisms alone. Peripheral factors—such as abnormal colonic transit and rectal evacuation, food intolerance, bile acid imbalance, microbiome alterations, enteroendocrine activity, Gamma-Aminobutyric Acid dysregulation, and genetic susceptibility to inflammation—also contribute. Accelerated colonic transit is associated with IBS with diarrhea (IBS-D), while impaired rectal evacuation is linked to IBS with constipation[5-7].

Functional constipation is a common FGID in children and is diagnosed based on the Rome IV criteria[8]. Occult constipation (OC) represents a clinically distinct and often under-recognized form of constipation, characterized by the absence of typical symptoms of constipation on initial medical history, despite objective evidence of fecal retention, such as hard stool on digital rectal examination or fecal impaction on plain abdominal radiography[9]. Unlike classical functional constipation, children with OC do not report hallmark features such as infrequent defecation or passage of hard stools, which may lead to underdiagnosis.

Instead, OC often presents with atypical or misleading symptoms, including recurrent abdominal pain (RAP), fecal incontinence, early satiety, frequent defecation with mucoid stools, postprandial defecation, a sensation of incomplete evacuation, abdominal fullness, abdominal distension, and nocturnal enuresis[10-12].

Overflow (paradoxical) diarrhea is a well-recognized manifestation of fecal impaction, in which liquid stool leaks around impacted fecal matter in the rectum, resulting in frequent, small-volume, and often involuntary watery stools[13,14]. This phenomenon can occur in both functional and OC and may be misinterpreted as primary diarrhea, further contributing to diagnostic confusion.

We often encounter patients who are diagnosed with IBS-D due to the frequent passage of loose stool and abdominal pain, secondary to OC. OC can often mimic IBS[12]. In children with IBS-D without any alarming signs, investigations are rarely advised, and a diagnosis is made on the basis of the Rome IV criteria. However, when symptoms do not improve with treatment, re-evaluation is warranted. Therefore, in that case, the diagnostic approach should first focus on ruling out OC. A plain abdominal radiograph may be a useful initial diagnostic tool to diagnose OC, and appropriate treatment may lead to symptom resolution without the need for costly or invasive investigations. Several scoring systems, including the Barr, Blethyn, and Leech scores, have been used to analyze plain abdominal radiographs for the diagnosis of OC. Among these, the Leech scoring system appears to be the most accurate and reliable, owing to its higher sensitivity and specificity in assessing fecal load on plain abdominal radiographs in children with constipation[15].

In this study, we analyzed patients who were primarily diagnosed with IBS-D and who failed to improve after proper management. We aimed to verify the hypothesis that OC may present with the features of IBS-D.

MATERIALS AND METHODS

Study design and setting

This prospective observational study was conducted at the Department of Pediatrics, Sylhet MAG Osmani Medical College and Dr. Benzamin’s Pediatric Liver Research Centre, Bangladesh, from mid-January 2022 to the end of December 2024.

Patient selection criteria

The study population consisted of consecutive pediatric patients referred with a preliminary diagnosis of IBS-D, established according to the Rome IV diagnostic criteria for IBS. All included patients had a history of at least three months of refractory symptoms, specifically abdominal pain and frequent loose stools (Bristol Stool Form Scale Type 6 or 7). Prior to enrollment, these patients had failed to improve on IBS-D management, including probiotics and antispasmodics (tiemonium methylsulfate). Additionally, they had received multiple courses of antibiotics (ciprofloxacin and metronidazole), zinc, and oral rehydration solutions. To exclude overflow diarrhea, we specifically included children who passed stools voluntarily and exhibited no overt clinical signs of constipation on initial history. Patients presenting with red-flag symptoms suggestive of organic disease (e.g., hematochezia or growth failure) were excluded from the study.

Diagnostic re-evaluation and the Leech score

As the patients failed to show symptomatic improvement, they underwent a structured re-evaluation following referral. Because features of OC may mimic IBS-D, a thorough physical examination—including digital rectal examination—and necessary investigations such as a plain abdominal radiograph were performed. If the rectum was found to be loaded with hard fecal matter, a diagnosis of overflow diarrhea was made. At any stage, if symptoms were suggestive of organic disease, the patient was evaluated further with appropriate investigations.

If the plain abdominal radiograph suggested fecal impaction (Figure 1), a diagnosis of OC was made. According to the Leech scoring criteria, fecal impaction was defined as a Leech score of 9 or higher on a plain abdominal radiograph[16]. Radiographs were independently assessed by two observers to minimize inter-observer variability. Initially, a total of 57 patients were enrolled in the study. All patients were thriving well and none had any alarming clinical features. During physical examination, three patients were diagnosed with overflow diarrhea, as they had hard fecal matter in the rectum along with fecal incontinence; therefore, they were excluded from the final analysis.

Figure 1  Plain X-ray of the abdomen showing impacted fecal matter in the right iliac fossa, and transverse and sigmoid colon.

Intervention and outcome measures

Upon confirmation of OC, patients received osmotic laxative therapy with magnesium hydroxide (400 mg/5 mL), administered at 1-2 mL/kg/day for a 2-month maintenance phase, followed by gradual tapering over 1 month.

The primary endpoints were resolution of abdominal pain and normalization of stool frequency and consistency. Patients were followed monthly for 4 months. Treatment outcomes included reduction in abdominal pain in terms of both intensity and frequency, along with resolution of diarrhea.

During the follow-up period, symptom monitoring was recorded by parents using a predesigned data sheet provided by the investigators. If any confusion arose, consultation with the research team was arranged.

Pain frequency was assessed by counting the number of pain episodes within a 24-hour period. Pain intensity was categorized into three subjective levels: (1) Mild: Complaint of pain without crying; (2) Moderate: Pain interfering with daily activities (e.g., playing or schooling) without crying; and (3) Severe: Pain associated with crying and interference with daily activities.

Defecation frequency was categorized into two groups: (1) ≥ 3 times/day with loose stool; and (2) < 3 times/day with normal stool. Stool consistency was assessed using the Bristol Stool Form Scale.

At the end of the 4-month follow-up period, treatment outcomes were categorized into three groups: (1) Poor response: Reduced pain frequency and intensity by < 50%. No change in stool frequency or consistency; (2) Satisfactory response: Reduced pain frequency and intensity by > 50%. Stool frequency and consistency normal; and (3) Good response: Reduced pain frequency and intensity by ≥ 80%. Stool frequency and consistency normal.

Statistical analysis

Data were analyzed using SPSS version 27. Symptom prevalence before and after intervention was compared using McNemar’s test and χ² test was used for categorical variables where appropriate. A P value < 0.05 was considered statistically significant.

RESULTS

A total of 54 patients were included in the final analysis and the mean age of the study population (n = 54) was 74.4 months, with a male-to-female ratio of 1.74:1. All patients (100%) presented with RAP, increased stool frequency (≥ 3 times/day), and loose stool consistency corresponding to type 6 or 7 on the Bristol Stool Form Scale. The mean duration of IBS-D related symptoms was 6.5 ± 1.5 months. A plain abdominal radiograph was performed, among whom 49 patients (90.7%) demonstrated fecal impaction with a Leech score ≥ 9, confirming the diagnosis of OC, while 5 patients (9.3%) showed no radiological evidence of fecal impaction.

Table 2 shows the comparison of clinical symptoms before and after treatment among the study participants. Prior to treatment, all patients (100%) had abdominal pain, increased stool frequency (> 3 times/day), and loose stool consistency (Bristol stool type 6 or 7). Following treatment, these symptoms markedly improved, with only 2 patients (4.1%) continuing to report abdominal pain, increased stool frequency, and loose stool consistency. The reduction in these symptoms was statistically significant (P < 0.001).

Table 2 Comparison of symptoms before and after treatment, n (%).

Symptoms	Before treatment	After treatment	P value
Abdominal pain	49/49 (100)	2/49 (4.1)	P < 0.0011
Stool frequency (> 3/day)	49/49 (100)	2/49 (4.1)	P < 0.0011
Bristol type 6 or 7	49/49 (100)	2/49 (4.1)	P < 0.0011
Anorexia	29/49 (59)	2/49 (4.1)	P < 0.0011
Nausea	15/49 (30)	2/49 (4.1)	P < 0.0011
Mucoid stool	10/49 (20)	0/49 (0)	P < 0.011
Bed wetting	5/49 (10)	0/49 (0)	P = 0.0631

¹McNemar’s test.

Other associated symptoms also showed significant improvement after treatment. Anorexia decreased from 29 patients (59%) to 2 patients (4.1%), and nausea decreased from 15 patients (30%) to 2 patients (4.1%). Mucoid stool, which was present in 10 patients (20%) before treatment, resolved completely after therapy. All of these improvements were statistically significant (P < 0.001). Bed wetting was present in 5 patients (10%) before treatment and resolved after therapy; however, the change did not reach statistical significance (P = 0.063).

Following treatment with osmotic laxative therapy, abdominal pain and stool frequency improved markedly within one month of treatment initiation, and the improvement was sustained for one month after withdrawal of maintenance therapy (Table 2).

Table 3 summarizes the treatment outcomes among patients with OC presenting with IBS-D like symptoms. At the end of follow-up, 44 patients (89.8%) were categorized as good responders, while 2 patients (4.1%) achieved satisfactory improvement. Two patients (4.1%) had persistent symptoms and were considered non-responders, warranting further evaluation for possible alternative pathologies. One patient (2.0%) was lost to follow-up. Overall, the treatment response among patients with OC was highly significant (P < 0.001).

Table 3 Occult constipation, treatment response, and cost comparison, n (%).

Variable	Result	P value
Occult constipation in unresponsive IBS-D (n = 54)	Yes: 49 (90.7)	P < 0.0011
	No: 5 (9.3)
Overall response after treatment (n = 49)	Good response: 44 (89.8)	P < 0.0011
	Satisfactory: 2 (4.1)
	No response: 2 (4.1)
	Lost to follow-up: 1 (2.0)
Presumptive treatment cost	Conventional method: 25000 BDT	98.4% cost reduction
	Our model: 400 BDT

¹χ² test.

IBS-D: Irritable bowel syndrome with diarrhea.

DISCUSSION

OC may present with a broad spectrum of symptoms secondary to fecal impaction, as large masses of hard, compressed stool cannot be expelled spontaneously[17].

In our study, children with OC frequently mimicked diarrhea-predominant IBS-D. They presented with frequent defecation, predominantly postprandial, with loose stools. The fecal impaction in the colon likely acts as a “gateway”, whereby liquid stool accumulates proximal to the obstruction and leaks around the impacted fecal mass, resulting in frequent, small-volume watery bowel movements[17,18]. Although this mechanism resembles overflow (paradoxical) diarrhea, the clinical presentation in our cohort differed, as the rectum was not persistently loaded and bowel movements were perceived as voluntary.

Approximately 24% of patients in our cohort had mucus-containing loose stools, locally described as “chronic dysentery”. Persistent contact between fecal matter and the colonic mucosa leads to mucosal irritation and excessive mucus secretion, accounting for this finding[17].

Abdominal pain was present in all patients and can be attributed to fecal impaction causing circumferential mechanical stretch of the bowel wall. This circumferential mechanical stretch alters gene expression (mechano-transcription) in the distended bowel, and mechano-transcription of nociceptive and inflammatory mediators play a critical role in the development of visceral hypersensitivity[19-21]. These findings support that the abdominal pain observed in our cohort was attributable to OC rather than IBS.

Regarding diagnosis, patients were treated empirically for constipation, with subsequent symptom resolution confirming the diagnosis. Two patients failed to respond and underwent further evaluation. These cases diverge from typical patterns of pediatric constipation, and comparable data in the literature remain limited. Notably, Tosto et al[12] reported that a proportion of patients initially diagnosed with IBS-D or IBS mixed may, in fact, have underlying functional constipation and should be managed accordingly. Our findings are consistent with this observation.

RAP imposes a significant burden on both children and their families, often leading to extensive and costly investigations. In the Netherlands, the cost of evaluating a single patient with RAP exceeds €2500[22]. In Bangladesh, our informal survey indicates that patients frequently undergo multiple investigations—including complete blood count, ultrasonography, urine analysis and culture, celiac panel, abdominal computed tomography, colonoscopy, and barium follow-through—at an approximate cost of 25000 BDT. In contrast, a plain abdominal radiograph costs approximately 400 BDT.

Based on our findings, we propose that in patients diagnosed with IBS-D according to Rome IV criteria who fail to respond to standard management, a plain abdominal radiograph should be considered to evaluate for OC. If suggestive findings are present, targeted treatment should be initiated. This approach has the potential to substantially reduce healthcare costs. While similar cost-saving implications were noted by Tosto et al[12], our model is strengthened by the systematic use of abdominal X-ray in all patients, enhancing its reliability and evidentiary basis. This study has several limitations. First, there is potential for selection bias, as only patients with presumed IBS-D who failed initial standard therapy were included, which may have led to an overestimation of the prevalence of OC in IBS-D. In addition, the small sample size, lack of a control group, subjective methods were used to grade the degree of pain and short follow-up period may limit the generalizability of the findings. Furthermore, the Leech scoring system is subject to inherent limitations, such as interpretative subjectivity and inter-observer variability. Future randomized controlled trials are needed to confirm and validate these results.

CONCLUSION

In children presenting with IBS-D like symptoms who fail to respond to standard therapy, OC should be actively considered. A simple abdominal radiograph may serve as a practical screening tool before proceeding to invasive or costly investigations.

ACKNOWLEDGEMENTS

The author’s heartfelt appreciation goes to all the children, parents and health workers, who participated in this study.