A 30-year-old woman with family history of hearing loss from her mother's side developed hearing problem during pregnancy. Hearing loss is bilateral, slowly progressive, with bilateral tinnitus that bothers her at night. Pure tone audiometry shows conductive hearing loss with an apparent bone conduction hearing loss at 2000 Hz. What is the most likely diagnosis?

Otosclerosis mostly involves females, has a positive family history and causes slow progressive bilateral hearing loss. Audiogram is characterized by Carhart's notch--a dip in bone conduction at 2000 Hz.Carhart's notch is loss of bone conduction in audiogram. It is a feature of otosclerosis. Loss is5 dB in 500 Hz10 dB in 1000 Hz15 dB in 2000 Hz5 dB in 4000 HzCarhart's notch. Note dip at 2 kHz in bone conduction