Nuclear imaging of inflammation in neurologic and psychiatric disorders

Cerebral inflammation is a common phenomenon during the progression of neurodegenerative diseases. In general, neurodegenerative diseases have unpredictable clinical courses and timely effective treatment is not available. For effective clinical trials on new drugs, suitable surrogate markers to monitor disease progression are required. The extent of cerebral inflammation could be such a surrogate marker. Nuclear imaging techniques, like positron emission tomography (PET) and single photon emission computed tomography (SPECT), have been applied to monitor inflammatory processes in patients. Neuroinflammation is accompanied by a variety of physiological changes, such as changes in cerebral glucose metabolism and perfusion, cyclooxygenase-2 overexpression and microglia activation. Nuclear imaging has utilized these physiological changes to visualize the inflammatory process in various chronic or acute neurodegenerative diseases. Expression of the peripheral benzodiazepine receptor in activated microglia proved a suitable specific marker to detect neuroinflammation. Currently, radiolabeled COX-2 inhibitors are under investigation for this purpose. The causative of neuroinflammation is often unknown, but the herpes simplex virus (HSV), for example, has been implicated in several neurodegenerative diseases. Recently, antiviral agents and antibiotics have been prepared that might be applicable to discriminate specific viral or bacterial infections. These radiolabeled compounds could also be used to monitor the drug pharmacokinetics noninvasively with PET. This review summarizes the progress that has been made in nuclear imaging of neuroinflammation in,neuropsychiatric diseases.