PET Case Study

A 64-year old female was referred to a senior neurologist for memory loss. The patient was having a progressive mental decline for the last two years but more precipitously six months ago when she could not recognize her husband. There were no localizing signs. Cranial MRI with and without contrast were negative with no evidence of infarction, mass or atrophy. Carotid ultrasound showed 50% stenosis of left internal carotid artery. The neurologist felt it was pre-senile dementia with depressive features, with a low probability of Alzheimer's disease. She dropped from 22 to 7 on a mini mental status exam over a 2 year period. She was referred for an FDG PET scan for further diagnosis.

The FDG PET scan was markedly abnormal. It showed large patches of significantly decreased radioactivity in both temporoparietal lobes more severe on the left consistent with decreased metabolism. The decreased uptake extended into the left frontal lobe. The scintigraphic pattern was compatible with fairly advanced Alzheimer's disease. The MRA done on the same day was normal, thereby excluding multi infarct dementia.

The definitive diagnosis of Alzheimer's disease is made only on autopsy. The clinical diagnosis of Alzheimer's disease can be difficult at times and the overall accuracy is often quoted as 50-80%. FDG PET imaging has been utilized for the diagnosis of Alzheimer's disease. Although the accuracy is not 100%, it is an important adjunct in the early diagnosis (or even late as in this case) of Alzheimer's Disease.