Forensic pathologist Dr Julie McAdam told Glasgow Sheriff Court that the cause of 50-year-old Margaret Gilchrist's death was "unascertained".
She said scalding could have killed her or it could have happened after death.
Ms Gilchrist died at her home in Glasgow - where she was cared for full-time - on 26 September 2013.
She had severe learning difficulties from birth, was registered blind and had epilepsy.
The FAI at Glasgow Sheriff Court had previously heard that Ms Gilchrist was found dead in the bath after being left for a short time by her carer.
Dr McAdam told the inquiry that her body was scalded all over - about 80% to 90% - in a way that was consistent with it being partly immersed in water.
She said it was also apparent that parts of her body were scalded in the water after she died.
Dr McAdam said that if Ms Gilchrist had sustained this amount of scalding while she was alive, that could potentially have killed her.
She said she could not be certain, however, whether this had happened.
The pathologist also said that Ms Gilchrist had a propensity for seizures, although she had not experienced one in many years.
Dr McAdam said that if Ms Gilchrist had suffered a seizure it could have rendered her unconscious, meaning she did not struggle or try to get out of the bath.
She said that may have played a role in her death.
The pathologist also told the court that Ms Gilchrist could have died from the scalds themselves.
She said shock from the pain of extremely hot water could have made Ms Gilchrist unconscious, then the scalding would have killed her.
The inquiry before Sheriff Lindsay Wood continues.
A fatal accident inquiry (FAI) into the death of a vulnerable woman in a bath has heard that she was found with scalds on about 90% of her body.