Table 1.

Disease subtypes of PACNS.

Subtype	Clinical features	MRI	Angiogram	Biopsy
Angiogram -negative biopsy-positive	cognitive impairment, greater CSF abnormalities, favourable response to treatment	meningeal and parenchymal enhancing lesions on MRI	negative	granulomatous pattern
Amyloid-β- related cerebral angiitis (ABRA)	older age, predominantly males, cognitive impairment	contrast-enhanced meningeal lesions	positive	granulomatous pattern with β- amyloid deposition in vessel walls
Meningeal enhancement in MRI	predominantly males, cognitive impairment, rapid response to treatment	prominent leptomeningeal enhancement	negative	granulomatous pattern
Spinal cord involvement	spinal cord symptoms, cerebral manifestations usually present	enhanced spinal (especially thoracic) lesions	negative	necrotizing pattern
Intracranial or subarachnoid haemorrhage	predominantly women, favourable response to treatment	intracranial or subarachnoid haemorrhage	positive	necrotizing pattern
Rapidly progressive	aggressive disease course, less responsive to treatment, often fatal outcome	bilateral, multiple, vessel lesions and infarctions	positive	granulomatous or necrotizing pattern

Classification according to Giannini and colleagues, 2012.⁴ Clinical and diagnostic features can overlap among disease subtypes.

CSF, cerebrospinal fluid; MRI, magnetic resonance imaging; PACNS, primary angiitis of the central nervous system