2.1. Study design, setting, and patient population

Children born between January 2014 and June 2019 and had new‐onset IESS, diagnosed between 2 months and 2 years of age with a minimum follow‐up of 2 years, at Boston Children's Hospital (BCH) were included. Patients were excluded if they lacked 2‐year follow‐up, were deceased, or were referred to BCH for a second opinion.

IESS patients were identified from the institutional data warehouse for IESS‐specific diagnosis codes (ICD‐9 codes: 345.60 and 345.61; or ICD‐10 codes: G40.821, G40.822, G40.823, and G40.824). We verified this list against BCH clinical note search utility (“Hound Dog”) searching for “infantile spasms,” “ACTH,” “prednisolone,” and “vigabatrin” through notes within the study's date range (2014‐2019).