Treatment strategies for Imerslund-Gräsbeck syndrome: a systematic review of vitamin B12 dosage and routes of administration

Abstract Purpose Imerslund-Gräsbeck syndrome (IGS) is a rare autosomal recessive disorder causing vitamin B12 malabsorption due to variants in CUBN or AMN . Current treatment relies on lifelong B12 supplementation, but standardized protocols are lacking. This systematic review synthesizes reported B12 regimens to evaluate dosing strategies and clinical outcomes. Methods A PRISMA-compliant systematic review of PubMed/Medline (inception–January 2026) for case reports/series detailing IGS treatment was conducted. Included studies provided explicit B12 dosage, route, and outcomes. Data from 27 studies (34 patients) were analyzed descriptively, with a heatmap comparing symptom resolution by administration route. The protocol registration number is CRD420251076543. Results Patients (mean age at onset: 6 years; 55.9% female) were treated with intramuscular (79.4%), oral (11.8%), or combined (8.8%) B12. A two-phase regimen (initial loading, then lifelong maintenance) was frequently employed. Hematologic and neurologic normalization were reported with both intramuscular (IM) and oral vitamin B12, with IM representing the standard, most reliably documented approach. Neurological recovery was linked to early treatment initiation. Molecular diagnosis was confirmed in 35% of patients. Conclusion IGS management predominantly uses intramuscular B12, but oral therapy may suffice in select cases. A two-phase dosing strategy (loading + maintenance) is widely employed, though optimal dosing requires further study. Early diagnosis and treatment are critical to prevent irreversible complications.