“…Our index patient and his third daughter fully fulfilled the current IHS criteria for ON, and two other family members fulfilled the current IHS criteria for ON except one criterion; namely, a decrease in pain by anesthetic block. Most ONs are idiopathic, but in rare cases, they may be a result of cervical spine osteochondroma [1], cavernoma [4, 5], multiple sclerosis, schwannoma [2, 8], meningioma [12], and myelitis [3, 9]. Though MRI examination was not conducted in all family members, the MRI results of the index patient and his second daughter had excluded local pathologies thus indicating idiopathic ON.…”