<prompt> All are reversible causes of dementia except -HypothyroidismHydrocephalusMeningoencephalitisAlzheimers disease  <response>: Ans. is d i.e., Alzhimers disease Reversible causes of dementia1 Surgically treatable :- Normal pressure hydrocephalus, brain tumors frontal lobe tumor, meningioma, subdural hematoma due to head injury, hydrocephalus.2 Medically treatable :- Depression, hypothyroidism, alcohol abuse, vitamin B JfolateNiacin deficiency, any metabolic or endocrine disturbance, neurosyphilis, Hashimotos encephalopathy, Wilsons disease, celiac disease, whipples disease, chronic meningoencephalitis, drugs and toxin toxic dementia.Irreversible causes of dementia :- Alzheimers disease, vascular multi-infarct dementia, Parkinsonism, Huntington 9s chorea, Lewy body dementia, Picks disease. 