Differential Diagnosis
- Single most likely diagnosis
- Celiac disease: The presence of tissue transglutaminase antibodies is a strong indicator of celiac disease, an autoimmune disorder that causes the immune system to react to gluten. The patient's symptoms of intermittent nonbloody diarrhea alternating with periods of constipation, along with failure to thrive (weight and height in the 10th percentile), are consistent with celiac disease. The normal thyroid function tests (TSH and thyroxine) help to rule out hypothyroidism as a cause of the gastrointestinal symptoms.
- Other Likely diagnoses
- Irritable Bowel Syndrome (IBS): Although the presence of tissue transglutaminase antibodies points towards celiac disease, IBS could be considered if the symptoms persist after a trial of a gluten-free diet. However, the failure to thrive and the specific laboratory findings make IBS less likely.
- Campylobacter gastroenteritis: This is less likely given the chronic nature of the symptoms (6 months) and the absence of bloody diarrhea, which is more commonly associated with Campylobacter infections.
- Do Not Miss (ddxs that may not be likely, but would be deadly if missed.)
- Crohn disease: Although the negative tests for anti-Saccharomyces cerevisiae antibodies and anti-flagellin antibodies decrease the likelihood of Crohn disease, it is crucial not to miss this diagnosis due to its potential for severe complications. The presence of chronic diarrhea, failure to thrive, and anemia (indicated by low hematocrit and hemoglobin) could still suggest Crohn disease, and further evaluation might be necessary.
- Hypothyroidism: Despite the normal thyroid function tests, hypothyroidism can sometimes present with gastrointestinal symptoms. However, given the normal TSH and thyroxine levels, this is less likely.
- Rare diagnoses
- Other rare causes of chronic diarrhea and failure to thrive in a child, such as immunodeficiency disorders or congenital infections, are not directly suggested by the information provided but could be considered if initial diagnoses are ruled out or if the patient does not respond to appropriate treatment for the most likely diagnosis.