PET Imaging May Accurately Diagnose Cerebral Amyloid Angiopathy (CAA)

Abstract & Commentary

By Alan Z. Segal, MD, Associate Professor, Department of Neurology, Weill-Cornell Medical College; Attending Neurologist, NewYork-Presbyterian Hospital. Dr. Segal is on the speaker's bureau for Boehringer Ingelheim.

Synopsis: PET imaging with Pittsburgh Compound B is a promising new technique to non-invasively diagnose CAA.

Source: Johnson KA, et al. Imaging of amyloid burden and distribution in cerebral amyloid angiopathy. Ann Neurol 2007;62:229-234.

The diagnosis of cerebral amyloid angiopathy (CAA) is made definitively on the basis of pathological examination of brain tissue. CAA also may be diagnosed indirectly based on multiple microhemorrhages on gradient echo MRI. The thioflavin derivative known as Pittsburgh Compound B (Pi-B) is known to bind to amyloid on PET imaging and has been used, as an investigational tool, in studies of Alzheimer's disease. Pi-B PET imaging also may be a useful method of diagnosing CAA in living subjects.

The authors studied six non-demented subjects with probable CAA, 15 healthy control subjects, and nine patients with probable Alzheimer's disease. PiB uptake was increased in CAA compared to healthy subjects, but was less than that seen in Alzheimer's patients. Importantly, CAA patients differed from Alzheimer's patients in showing an occipital predilection for Pi-B uptake, with a significantly increased occipital to global ratio. As the authors observe, this occipital predominance, known to occur in the pathology of CAA, may help tease out vascular as opposed to plaque amyloid burden.

Commentary

This study has important clinical implications since CAA may pose a major risk for intracerebral hemorrhage in elderly patients requiring warfarin therapy for atrial fibrillation and other indications. Pi-B PET imaging may potentially diagnose CAA non-invasively in patients with isolated hemorrhage or even among patients who have never had an intracerebral hemorrhage. Validation in a larger study is warranted, and pathologic confirmation will be important.