Bottomline:  First human study demonstrates increased arachidonic acid levels in the brains of Alzheimer's patients, indicative of inflammation.  Journal of Nuclear Medicine (Sept 2008) Vol. 49 No. 9 1414-1421.

Background: Previous studies demonstrating inflammation compounds in the brains of patients with Alzheimer's disease, together with animal imaging studies showing neuroinflammation with elevated arachidonic acid, led researchers to believe that this omega-6 fatty acid is likely elevated in the brains of humans with this disorder.

Summary: Researchers developed a method to view neuroinflammation in brain in 8 patients with Alzheimer's disease and compared them to age-matched controls.  Arachidonic acid was elevated in widespread cortical areas of the brain in mildly to moderately (1 severely) demented but otherwise healthy patients with Azheimer's disease, compared with age-matched controls.  Notably, arachidonic acid was particularly elevated in brain regions reported to have high densities of senile (neuritic) plaques  as shown:

These results indicate that elevated arachidonic acid is associated with Azheimer's disease, which is consistent with previous studies showing upregulated markers of brain arachidonic acid metabolism in a rat model of neuroinflammation and on the presence of neuroinflammation in Alzheimer's disease.

Comment: The increase of the arachidonic acid cascade and ensuing inflammation has been implicated in other disorders (See Arachidonic Acid-The Omega-6 Fat Connection to Bipolar Mood Disorder and Medications that Block Effects of Omega-6 Fat and Arachidonic Acid: The Omega-6 Fat Linked to Alzheimer's Disease )

Link to Study:
Esposito G. et al. Imaging Neuroinflammation in Alzheimer's Disease with Radiolabeled Arachidonic Acid and PET.  Journal of Nuclear Medicine (Sept 2008) Vol. 49 No. 9 1414-1421.