A brief review of literature is made on the problem of modern classification, diagnosis and treatment of systemic vasculitis. The authors present a clinical case of a 40-YO male, in whom the disease started with focal neurological signs: epileptic seizures, disorder of consciousness, light euphoria, nasolabial fold insufficiency and left upper extremity hypoesthesia. Initial examination revealed upper sagittal sinus together with right lateral sinus thrombosis with forming of bilateral frontal lobe’s hemorrhages; development of stable thrombocytopenia and platelet antibodies in blood species as well as hyperhomocysteinemia and a MTHFR gene mutation. Further, the patient was followed-up by the hematologist and treated by steroids. Systemic vasculitis of granulomatosis with polyangiitis (Wegener’s granulomatosis) and eosinophilic granulomatosis with polyangiitis (Churg—Strauss syndrome) were late diagnosed in this patient, and coexistence of two systemic vasculitis predetermined extremely severe course of the disease with fatal outcome in nearly 5 years after the disease started, and after steroid and rituximab treatment. It is concluded that the diagnosis of cerebral venous thrombosis in a young patient should exclude systemic vasculitis as one of its possible causes.