Prospective Flutemetamol Positron Emission Tomography and Histopathology in Normal Pressure Hydrocephalus

Backgound/Objective: To determine the level of association between uptake of the amyloid positron emission tomography (PET) imaging agent [ 18 F]flutemetamol and the level of amyloid-ß measured by immunohistochemical and histochemical staining in a frontal cortical region biopsy site. Methods: Seventeen patients with probable normal pressure hydrocephalus (NPH) underwent prospective [ 18 F]flutemetamol PET and subsequent frontal cortical brain biopsy during ventriculoperitoneal shunting. Tissue amyloid-ß was evaluated using the monoclonal antibody 4G8, thioflavin S and Bielschowsky silver stain. Results: Four of the 17 patients (23.5%) had amyloid-ß pathology based on the overall pathology read and also showed increased [ 18 F]flutemetamol uptake. [ 18 F]Flutemetamol standardized uptake values from the biopsy site were significantly associated with biopsy specimen amyloid-ß levels (Pearson's r = 0.67; p = 0.006). There was also good correlation between the biopsy specimen amyloid-ß level and uptake of [ 18 F]flutemetamol in the region contralateral to the biopsy site (r = 0.67; p = 0.006), as well as with composite cortical [ 18 F]flutemetamol uptake (r = 0.65; p = 0.008). The blinded visual read showed a high level of agreement between all readers (κ = 0.88). Two of 3 readers were in full agreement on all images; 1 reader disagreed on 1 of the 17 NPH cases. Blinded visual assessments of PET images by 1 reader were associated with 100% sensitivity to the overall pathology read, and assessments by the 2 others were associated with 75% sensitivity (overall sensitivity by majority read was 75%); specificity of all readers was 100%. Conclusions: [ 18 F]Flutemetamol detects brain amyloid-ß in vivo and shows promise as a valuable tool to study and possibly facilitate diagnosis of Alzheimer's disease both in patients with suspected NPH and among the wider population.