The girl was kept in "appalling conditions" between the ages of three and five. When social workers finally broke through wooden planks to rescue her she was found whimpering in her room begging for a drink.
The court was told how the girl was first discovered boarded up in the room in May 1996 when she was just three. But the youngster was not taken into council care until 15 months later.
Social services officials tonight blamed a previous council for not protect her.
Her parents, who cannot be named, were jailed for six months after admitting child cruelty.
Prosecuting at Cardiff Crown Court, Mr Ieuan Bennett said during a routine visit in May 1996 a social worker noted the youngest daughter was missing.
He said: "When she went to investigate she found the girl in the room. The door to the bedroom had been removed and wooden boards had been nailed across it up to a height of 5ft.
"Conditions were filthy - in contrast with the rest of the house. .
"Her brothers and sisters were kept in comfort. It seems the parents singled out their youngest daughter for this treatment and she was made into a scapegoat."
The court heard all the windows except for a tiny skylight were boarded up and the only furnishing in the room was a dirty mattress. The girl was not allowed to go to the toilet and the walls were caked in faeces. There was no carpet and her parents forbade toys.
Social workers made regular visits to the house in Caerphilly, Mid Glamorgan, and conditions began to improve.
But as soon as the social work visits stopped the parents again "caged" their daughter inside the room.The pair were eventually arrested last year.
Dr Dewi Evans, a consultant paediatrican at Singleton Hospital, Swansea, told the court: "This is the worst case of gross emotional deprivation I have met in my 18 years in the job."
Dr Evans criticised social workers for not taking the girl into care when they found her.
The parents told police they had boarded up the room for the girl's own safety to stop her wandering around the house.
Sentencing, Judge Christopher Morton told the couple: "You caged your daughter in that room and left her in a very distressed state. But you are intellectually limited and your other children need you so the sentence is much shorter than it otherwise would have been."
The girl has since been rehoused with foster parents.Reuse content