IgG4-Related Disease Associated with Pearson Syndrome: A Case of Rapid Decline

We report a diagnostically challenging case of a 1-year-old female with refractory thrombocytopenia, sideroblastic anemia, pancreatitis and metabolic decompensation, ultimately attributed to coexisting IgG4-related disease (IgG4-RD) and Pearson syndrome (PS) —a previously undocumented association. Key findings of the case were 1. Treatment resistant thrombocytopenia despite IVIG, corticosteroids, and eltrombopag (transient response only). 2. Elevated IgG4 (840 μg/mL) and pancreatitis thought to be secondary to IgG4-RD. 3. Mitochondrial DNA deletion (m. 10052₁5604 del, 93. 2% heteroplasmy) and ringed sideroblasts secondary to PS. 4. Fatal Metabolic Crisis with hyperlactatemia (peak 8. 4 mmol/L) and cardiac failure, underscoring PS's rapid progression. This is the first reported association between IgG4-RD and PS, highlighting the need for dual-pathology evaluation in refractory cytopenia with metabolic disturbances.