Congenital Rubella Syndrome — Progressive SNHL

A 3-year-old boy with congenital rubella syndrome presents for audiologic re-evaluation. His mother had confirmed rubella infection at 8 weeks of gestation with positive rubella-specific IgM. The child was born with intrauterine growth restriction, blueberry muffin rash, hepatosplenomegaly, thrombocytopenia, patent ductus arteriosus, and bilateral nuclear cataracts. Newborn screening showed absent otoacoustic emissions bilaterally. Current pure-tone audiometry reveals the pattern marked **A** in the diagram. Compared with his 2-year-old audiogram, his thresholds have worsened by 20 dB. Which of the following best explains the progressive nature of the sensorineural hearing loss in this child?