senile dementia 
noun [mass noun]
Dementia occurring in old age as a result of progressive brain degeneration.The diagnosis was schizophrenia, complicated by senile dementia and congestive heart failure....
- People with senile dementia get paranoid bursts - my mother thought we were stealing her light bulbs, and she would stay awake all night convinced there was a man in black at the end of her bed, beckoning to her.
- In addition, nursing homes charge an extra fee if the patient requires 24-hour nursing care or is suffering from senile dementia or Alzheimer's disease.