Successful Early Therapy With Sirolimus for an Infant With Primary Intestinal Lymphangiectasia.

INTRODUCTION: Identifying the cause of protein-losing enteropathy (PLE) is crucial for appropriate treatment. Primary intestinal lymphangiectasia (PIL) is a cause of PLE, and low-strict fat diet with medium-chain triglyceride (MCT) supplementation may be insufficient. Sirolimus has shown efficacy in refractory PIL; however, its use in infants remains uncommon, and the optimal timing of initiation has not been established. CASE PRESENTATION: A previously healthy 7-month-old Japanese male infant presented with convulsions, generalized edema, and diarrhea. Laboratory findings revealed severe hypoproteinemia (serum albumin: 1.3 g/dL), lymphopenia (absolute lymphocyte count: 822/μL), and electrolyte abnormalities. Scintigraphy using 99mTc-labeled human serum albumin showed tracer exudate in the small intestine, leading to the diagnosis of PLE. Upper endoscopy revealed snowflake-like white spots in the duodenum, and pathological examination confirmed lymphatic dilation, leading to a PIL diagnosis. Despite treatment with a low-strict fat diet with MCT supplementation and corticosteroids, hypoproteinemia persisted. Lymphatic scintigraphy and magnetic resonance lymphangiography confirmed ongoing protein leakage. Sirolimus was initiated at 0.5 mg/day on Day 23. Subsequently, serum albumin began to increase within 1-2 weeks and ultimately reached 4.1 g/dL, and absolute lymphocyte count, 1917/μL immediately before sirolimus initiation, increased to 3843/μL. Lymphatic scintigraphy on Day 74 of sirolimus treatment showed complete resolution of protein leakage. Sirolimus was continued for 121 days and discontinued thereafter. At 17 months of follow-up, no recurrence was observed, with sustained normalization of serum albumin to 4.0 g/dL and absolute lymphocyte count to 4739/μL. DISCUSSION: This case suggests one of the earliest reported responses to sirolimus in the treatment of PIL, with improvement observed within a few weeks of initiation. Early introduction of sirolimus in patients with persistent protein leakage resistant to low-strict fat diet with MCT supplementation may be associated with rapid improvement in PIL, though this hypothesis warrants further case accumulation.