Cerebral amyloid angiopathy

Cerebral amyloid angiopathy
Congo red stain
Classification and external resources
Specialty
ICD-10	I68.0
DiseasesDB	32874
MedlinePlus	000719
eMedicine	neuro/628
Patient UK	Cerebral amyloid angiopathy
MeSH	D016657

Cerebral amyloid angiopathy (CAA), also known as congophilic angiopathy, is a form of angiopathy in which amyloid deposits form in the walls of the blood vessels of the central nervous system. The term congophilic is used because the presence of the abnormal aggregations of amyloid can be demonstrated by microscopic examination of brain tissue after application of a special stain called Congo red. The amyloid material is only found in the brain and as such the disease is not related to other forms of amyloidosis.

Signs and symptoms

Since this can be caused by the same amyloid protein that is associated with Alzheimer's dementia, brain bleeds are more common in people who suffer from Alzheimer's, however they can also occur in those who have no history of dementia. The bleeding within the brain is usually confined to a particular lobe and this is slightly different compared to brain bleeds which occur as a consequence of high blood pressure (hypertension) - a more common cause of a hemorrhagic stroke (or bleeding in the brain).

Causes

CAA has been identified as occurring either sporadically (generally in elderly populations) or in familial forms such as Flemish, Iowa, and Dutch types.In all cases, it is defined by the deposition of Aβ in the leptomeningal and cerebral vessel walls. CAA occurring in the Flemish type has been observed to be linked to large dense-core plaques observed in this pedigree.

The reason for increased deposition of Aβ in sporadic CAA is still unclear with both increased production of the peptide and abnormal clearance having been proposed as potential causes. Under normal physiology Aβ is cleared from the brain by four pathways: (1) endocytosis by astrocytes and microglial cells, (2) enzymatic degradation by neprilysin or insulysin(3) cleared by way of the blood brain barrier or (4) drained along periarterial spaces. Abnormalities in each of these identified clearance pathways have been linked to CAA.

In familial forms of CAA, the cause of Aβ build up is likely due to increased production rather than poor clearance. Mutations in the amyloid precursor protein (APP), Presenilin (PS) 1 and PS2 genes can result in increased rates of cleavage of the APP into Aβ.An immune mechanism has also been proposed.

Diagnosis

MRI showing low signal foci in cerebral amyloid angiopathy. Conventional gradient echo T2*-weighted image (left, TE=20ms), susceptibility weighted image (SWI) and SWI phase image (center and right, respectively, TE=40ms) at 1.5 Tesla.

Susceptibility weighted imaging has been proposed as a tool for identifying CAA-related microhemorrhages. Biopsies also play a role in diagnosing the condition.

Types

It is usually associated with amyloid beta.

However, there are other types:

• the "Icelandic type" is associated with Cystatin C
• the "British type" is associated with ITM2B

Research is currently being conducted to determine if there is a link between cerebral amyloid angiopathy and ingestion of excessive quantities of aluminum.