Avoidant/restrictive food intake disorder complicated by superior mesenteric artery syndrome in an adolescent male with Klinefelter syndrome: A case report.

Background: Avoidant/restrictive food intake disorder (ARFID) is characterized by restrictive or avoidant eating not driven by weight or shape concerns and is often associated with autism spectrum disorder (ASD). Superior mesenteric artery (SMA) syndrome may occur in ARFID with significant weight loss; however, overlapping gastrointestinal symptoms may obscure its recognition. Case Presentation: A 16-year-old boy with a history of ASD and Klinefelter syndrome (47,XXY) presented with postprandial nausea, abdominal pain, fatigue, and rapid weight loss. He had chronic sensory hypersensitivity-related selective eating since early childhood and maintained a slender body habitus. Upon admission, his height and weight were 182 cm and 40.7 kg, respectively (body mass index [BMI] = 12.3). He had no drive for thinness, fear of weight gain, or body image disturbance and was diagnosed with ARFID. Abdominal ultrasonography revealed marked narrowing of the SMA-aorta angle (6.8°) and distance (3 mm), with duodenal compression, consistent with SMA syndrome. Enteral nutrition was initiated and gradually increased, accompanied by psychoeducation, meal support tailored to sensory sensitivities, and behavioral interventions. He showed weight restoration and improvement in gastrointestinal symptoms and duodenal obstruction, allowing a gradual transition to oral intake. Upon discharge, his weight was 49.0 kg (BMI = 14.8). Follow-up ultrasonography revealed partial improvement in the SMA-aorta angle. Conclusion: SMA syndrome should be considered in patients with ARFID who present with gastrointestinal symptoms and rapid weight loss. Klinefelter syndrome may increase vulnerability to SMA syndrome, complicating clinical recognition. Combining nutritional rehabilitation, medical evaluation, and psychosocial interventions is important for effective complex eating disorder management.