ABSTRACT
Allergic proctocolitis (AP) can be hard to differentiate and diagnose in neonates who manifested watery diarrhea and failure to thrive. The initial symptoms are not specific and colonoscopic findings share similar ulcerated and erythematous lesions as in ulcerative colitis of infancy and infectious colitis. A 3-day-old infant was admitted to the hospital due to loose, blood-tinged stools. An initial workup, including abdominal ultrasound and hepatobiliary scan, was performed, and all results were negative. The patient subsequently required readmission due to pervasive watery diarrhea, severe weight loss, and lethargy. After further investigation, he was eventually diagnosed of allergic proctocolitis by rectosigmoidoscopy and biopsy. Treatment was started with a corticosteroid (prednisone 2 mg/kg/day) due to severe symptoms. After 7 days of steroid therapy, the stools slowly normalized, and the patient started to gain weight. He was discharged home and followed regularly at the outpatient clinic.