Alzheimers after long-term lithium use

Hi, welcome to the ehealth forum and I am glad to help you.
You seem concerned that your mom has never been under supervised psychiatric care and has been on lithium for the last 30 years and recently she has been diagnosed with Alzheimer's disease.
As a mood stabilizer, lithium is probably more effective in preventing mania than depression, and may reduce the risk of suicide. In depression alone (unipolar disorder) lithium can be used to augment other antidepressants. Those who use lithium should receive regular serum level tests and should monitor thyroid and kidney function for abnormalities. In long-term use, therapeutic concentrations of lithium have been thought to cause histological and functional changes in the kidney. The significance of such changes is not clear, but is of sufficient concern to discourage long-term use of lithium unless it is definitely indicated. Doctors may change a bipolar patient's medication from lithium to another mood stabilizing drug, such as Depakote (divalproex sodium), if problems with the kidneys arise. An important potential consequence of long-term lithium usage is the development of renal diabetes insipidus (inability to concentrate urine). Patients should therefore be maintained on lithium treatment after 3–5 years only if, on assessment, benefit persists. That is why your mother needed regular psychiatric consultation to review the need for continuing lithium .
Bipolar disease is associated with increased incidence of dementia. At therapeutic concentrations, lithium inhibits glycogen synthase kinase-3, a key enzyme in the metabolism of amyloid precursor protein and the phosphorylation of tau protein (Klein & Melton, 1996;Lovestone et al, 1999) which are critical steps in the formation of neuritic plaques and neurofibrillary tangles, the pathological hallmarks of Alzheimer’s disease. Therefore, it is seen in some studies that exposure to chronic lithium treatment might protect elderly patients with bipolar disorder against Alzheimer’s disease. Your mother developed Alzheimer's as the risk itself is increased in Bipolar disorder and is decreased by chronic lithium therapy but can never be brought to null.
Hope this helps. Take care.
Note: This answer is not intended as and does not substitute for medical advice - the information presented is for patient education only. Please see your personal physician for further evaluation of your individual case.