Table 2.

Clinical symptoms, laboratory and radiological features specific for the conditions mimicking PACNS.

Rheumatological causes [5,6,15,16,18].	Arthritis, skin changes, Raynaud phenomenon, ocular, lung, or kidney involvement Systemic symptoms Peripheral nervous system (PNS) involvement Elevated ESR and CRP Hypochromic anemia Low complement levels Elevated antibody titers: antinuclear antibodies extractable nuclear antigen antibodies antineutrophil cytoplasmic antibodies antiphospholipid antibodies rheumatoid factor
Infectious causes [5,6,10,15,16,18,23].	Positive serology for: Viral infections: varicella-zoster virus (VZV), human immunodeficiency virus (HIV), hepatitis C virus, cytomegalovirus, parvovirus B19 Bacterial infections: Treponema pallidum, Borrelia burgdorferi, Mycoplasma pneumoniae, Bartonella henselae, Rickettsia, Mycobacteria Fungal infections: aspergillosis, mucor-mycosis, coccidioidomycosis, candidosis
Malignancies (intravascular lymphoma, gliomatosis) [5,6,15,16,18].	History of malignancy Specific MRI spectroscopy findings Atypical cells on the brain biopsy
Reversible cerebral vasoconstriction syndrome [5,6,15,16,18].	Acute onset, thunderclap headache Normal cerebrospinal fluid findings Brain MRI normal in 70% of patients Angiographic findings similar to PACNS but usually reversible within 6–12 weeks No inflammatory changes on the brain biopsy
Multiple sclerosis [10].	Less contrast-enhancing lesions (compared to PACNS in which 90% of lesions enhance contrast) No vessel wall changes
Anti-MOG encephalitis [23].	Positive MOG antibodies in the CSF No vessel wall changes Absence of fibrinoid necrosis of the vessel wall on the brain biopsy
Sneddon’s syndrome [16].	Younger women are affected (20–40 y.o.) Livedo rash Antiphospholipid antibodies positive in 50–80% Headache is not so common Psychiatric complications occur later in the course of the disease

PACNS—primary angiitis of the central nervous system; ESR—erythrocyte sedimentation rate; CRP—C-reactive protein; MRI—magnetic resonance imaging; MOG—myelin oligodendrocyte glycoprotein; CSF—cerebrospinal fluid.