What are the main causes of subileus in a 4-year-old afebrile girl with a 4-week history of nightly vomiting and daily diarrhea, normal blood work, urine and stool tests, leukocytosis in urine, and a firm abdomen with gas, suggesting a possible gastrointestinal motility disorder?

Differential Diagnosis of Subileus in a 4-Year-Old Child

In this 4-year-old with subileus, normal infectious workup, and 4-week duration of symptoms, the primary differential includes functional intestinal pseudo-obstruction, chronic constipation with fecal impaction, and less likely but critical to exclude—intermittent malrotation with volvulus or intussusception. 1, 2

Immediate Life-Threatening Causes to Exclude

Malrotation with intermittent volvulus must be ruled out urgently despite the 4-week duration, as this can present at any age and may have intermittent symptoms before complete obstruction develops. 1, 2 The planned contrast fluoroscopy study tomorrow is appropriate to evaluate the position of the duodenojejunal junction (ligament of Treitz) and assess for malrotation. 1

Key Features Supporting or Against Volvulus:

• Against volvulus: Afebrile status, 4-week duration without deterioration, absence of bilious vomiting (critical—bilious vomiting would indicate obstruction distal to ampulla of Vater and constitute a surgical emergency). 1, 2
• Concerning features: Progressive abdominal distension (from soft to firm), inability to pass gas except with diarrhea, radiographic subileus pattern. 1

Intussusception typically presents with crampy intermittent pain, "currant jelly" stools, and progression to bilious vomiting, but can occasionally have atypical presentations in this age group. 1 The absence of bloody stools and the chronic nature make this less likely, but the contrast study will help exclude this.

Most Likely Functional/Motility Causes

Chronic Intestinal Pseudo-Obstruction (CIPO)

This represents the most likely diagnosis given the constellation of findings: 3, 4

• Chronic vomiting and diarrhea over 4 weeks
• Progressive abdominal distension with gas and slow-moving content on ultrasound
• Inability to pass gas spontaneously
• Subileus pattern on radiograph without mechanical obstruction
• Normal infectious and inflammatory workup

CIPO is characterized by impaired gastrointestinal propulsion mimicking mechanical obstruction without an anatomic lesion. 3, 4 The alternating pattern of vomiting (mostly nocturnal) with diarrhea suggests disordered motility affecting multiple segments of the GI tract. 3

Severe Functional Constipation with Overflow Diarrhea

The "paradoxical diarrhea" (watery yellow or diluted porridge-like stool) alongside inability to pass gas and progressive abdominal firmness suggests fecal impaction with overflow incontinence. 5 The rock-hard abdomen with gas and stagnant content supports significant fecal loading despite the diarrhea. 5

Gastroparesis or Generalized Dysmotility

Delayed gastric emptying can cause chronic vomiting and secondary intestinal dysmotility, particularly the nocturnal pattern of vomiting which is characteristic of gastroparesis. 6, 7 The ultrasound finding of slow-moving content throughout the GI tract supports a generalized motility disorder rather than isolated gastroparesis. 6, 7

Secondary Considerations

Post-Infectious Dysmotility

Despite negative stool studies now, a preceding viral gastroenteritis could have triggered persistent dysmotility. 5 The initial leukocytosis in urine (likely from dehydration rather than infection) and the 4-week timeline are consistent with post-infectious gut dysfunction. 5

Metabolic or Endocrine Causes

Although blood work is reported as normal, specific evaluation for hypothyroidism, celiac disease, and electrolyte abnormalities (particularly hypokalemia and hypomagnesemia) should be confirmed, as these can cause intestinal pseudo-obstruction. 3, 4

Critical Diagnostic Steps

The contrast fluoroscopy study (upper GI series with small bowel follow-through) planned for tomorrow is the single most important next step to: 1, 2

1. Definitively exclude malrotation (abnormal position of ligament of Treitz)
2. Identify any mechanical obstruction (strictures, webs, duplications)
3. Assess transit time and motility patterns throughout the GI tract
4. Evaluate for intermittent obstruction

Additional Workup to Consider:

• Rectal examination and possibly rectal biopsy if Hirschsprung disease is suspected (though typically presents in infancy, late-onset forms exist). 2
• Abdominal CT with contrast if the fluoroscopy is non-diagnostic and symptoms persist, to evaluate for masses, inflammatory processes, or anatomic abnormalities not visible on plain films. 5
• Gastric emptying study if upper GI series shows no mechanical obstruction, to quantify gastroparesis. 6, 7

Management Approach Pending Diagnosis

Maintain NPO status or clear liquids only until mechanical obstruction is excluded by contrast study. 1, 2 If the child becomes bilious at any point, this constitutes a surgical emergency requiring immediate surgical consultation. 1, 2

Ensure adequate IV hydration and electrolyte repletion, as chronic vomiting and diarrhea place the child at risk for dehydration and electrolyte abnormalities. 5

Nasogastric decompression may be warranted if abdominal distension worsens or vomiting becomes more frequent, to relieve gastric distension and reduce aspiration risk. 4

If Mechanical Obstruction is Excluded:

• Prokinetic agents (erythromycin or metoclopramide) may be considered for documented gastroparesis or generalized dysmotility. 6, 4
• Aggressive bowel regimen with polyethylene glycol if fecal impaction is confirmed, though this must wait until mechanical obstruction is excluded. 5
• Pediatric gastroenterology consultation for consideration of manometry studies if CIPO is suspected. 3

Critical Pitfalls to Avoid

Do not assume this is simply constipation or gastroenteritis given the 4-week duration and progressive abdominal distension. 1, 2 The subileus pattern demands exclusion of mechanical causes before attributing symptoms to functional disorders. 1, 2

Do not start prokinetic agents or aggressive laxative therapy before excluding mechanical obstruction, as this could precipitate perforation if an anatomic lesion is present. 4

Monitor closely for development of bilious vomiting, peritoneal signs, or hemodynamic instability, any of which would require immediate surgical evaluation. 1, 2