Cerebral vasculitis in adults: what are the steps in order to establish the diagnosis? Red flags and pitfalls
成人腦血管炎：確定診斷的步驟是什麼？危險信號和陷阱

Reliable clinical suspicion
可靠的臨床懷疑

The first and most important step in the diagnostic work-up is detailed anamnesis and clinical examination, including asking for drug abuse, former medical conditions, characterization of symptoms, especially headaches [3–5], and family medical history. Medical examination should focus on skin or other systemic signs for rheumatic or non-inflammatory diseases (Fig. 2) [6–8].
診斷檢查的第一步也是最重要的一步是詳細的病史和臨床檢查，包括詢問是否濫用藥物、先前醫療狀況、症狀特徵，尤其是頭痛。 3 – 5 ]，以及家族病史。身體檢查應著重於皮膚或其他全身體徵是否有風濕性或非發炎性疾病（圖 1）。 2 ）[ 6 – 8 ]。

Patients presenting with multi-focal symptoms accompanied by headache, psychiatric symptoms and signs of a systemic inflammatory disorder need a diagnostic work-up in order to exclude or detect cerebral angiitis [9–12]. In particular, younger stroke patients without classical vascular risk factors, patients with clinical signs of a rheumatic disease, i.e. arthritis, Raynaud phenomenon, red eye, lung or kidney affection, and those with inflammatory laboratory findings [high erythrocyte sedimentation rate (ESR), C-reactive protein (CRP), anaemia or cerebrospinal fluid (CSF) pleocytosis] may suffer from an angiitis [13]. The combination of neurological symptoms and signs of a systemic disease need an extensive diagnostic work-up [9,11,14].
出現多灶性症狀並伴隨頭痛、精神症狀和全身性發炎疾病徵象的患者需要進行診斷檢查，以排除或檢測腦血管炎。 9 – 12 ]。特別是，沒有典型血管危險因子的年輕中風患者，有風濕病臨床症狀的患者，即關節炎、雷諾氏現象、紅眼、肺部或腎臟病變，以及有發炎實驗室檢查結果的患者[紅血球沉降速率（ ESR）高， C反應蛋白（CRP）、貧血或腦脊髓液（CSF）細胞增多]可能患有血管炎[ 13 ]。神經系統症狀和全身性疾病徵象的結合需要進行廣泛的診斷檢查。 9 , 11 , 14 ]。

First diagnostic steps in suspected cerebral vasculitis

All patients need a laboratory work-up focusing on inflammation and antibody-mediated diseases [9,15]. Raised acute phase proteins (high ESR, CRP), hypochromic anaemia and low complement are typical findings in the systemic vasculitides. Depending on the underlying condition, anti-neutrophil cytospasmic antibodies (ANCA) or anti-nuclear antibodies (ANA) are detected with high titres [15]. The typical picture in the CSF is a mild lymphocytic pleocytosis combined with an elevated protein level. Oligoclonal banding may occur temporarily [16].

In order to detect a cerebral vasculitis, MRI studies, including diffusion, gradient echo and contrast enhanced T1 sequences, are necessary [9,17,18]. Frequently, both new and older ischaemic lesions are detected; the combination of ischaemic and haemorrhagic lesions is not uncommon. Diffuse white matter lesions suggestive for microangiopathies are frequently observed. Prominent gadolinium-enhancement of the leptomeninges is rare [19,20]. Gadolinium-enhanced intracerebral lesions are observed in about one-third of patients [16].

Special techniques such as ‘Black Blood MRI’ [21], contrast-enhanced vessel MRI or positron emission tomography (PET) imaging may be helpful in order to visualize the inflammation of the vessel wall directly [18,22]. While these techniques have been studied extensively in the variants of giant cell arteritis (GCA) [23,24], data for the other vasculitides are sparse. In the cranial variant of GCA, ultrasound studies with duplex sonography demonstrating the halo sign are highly sensitive and specific [25].

Despite suggestive MRA or CTA, conventional angiography is often mandatory (Fig. 3). Alternating areas of narrowing and dilatation or multi-locular occlusions of intracranial vessels are highly suggestive of vasculitis. However, it should be considered that the ‘typical’ suspicion of vasculitis in angiography is often caused by differential diagnoses such as reversible cerebral vasoconstriction syndrome (RCVS) or other non-inflammatory diseases [4]. Moreover, small-vessel vasculitis is associated typically with negative cerebral angiography [26,27].

In the case of CNS affection in systemic biopsy-proven vasculitis additional brain biopsy is often expendable; however, exclusion of other causes of neurological symptoms such as progressive multi-focal leucencephalopathy or medication side effects is extremely important [28,29].

Diagnosis of definitive vasculitis

Once the tentative diagnosis of cerebral angiitis is established, it must be clarified if the patient suffers from the manifestation of a systemic disease, or whether a primary angiitis of the CNS (PACNS) is the underlying pathology [9,30].

The diagnostic criteria [15] for PACNS include acquired neurological symptoms or findings not explained after a thorough diagnostic assessment, a cerebral angiography demonstrating the features of vasculitis and a CNS biopsy sample demonstrating angiitis [10,16]. Any other disorder including the systemic vasculitides to which the angiographic or pathological features might be secondary must be excluded [30].

PACNS is an uncommon disease in which lesions are limited to the brain and spinal cord. The condition is very rare, with an estimated incidence from 2·4:1 million to fewer than 1:2 million [31]. Since the first histological description in 1922, approximately 500 cases have been published worldwide [31]. Recently, a working group from the Mayo Clinic published a series of 101 patients with PACNS seen over two decades from 1983 to 2003 [10]. We identified 21 patients treated at Alfried Krupp Hospital, Essen, Germany between 2003 and 2008 with a diagnosis of definite PACNS [16]. The most frequent clinical presentations are cerebral ischaemia (75%), headache (60%) and altered cognition (50%) [8,16]. Intracranial haemorrhage is infrequent.

Almost all patients show MRI abnormalities. Ischaemic infarctions with diffusion disturbances are seen in 75%; signs of microangiopathy are present in 65%. Gadolinium-enhanced lesions are detected more frequently with amnestic syndromes at disease onset and with gait disturbances. MR-angiography (MRA) is suggestive of vasculitis in 45% [22]. MRI of PACNS may be suspicious for brain tumour, and PACNS mimicking tumour-like lesions is often diagnosed by biopsy by chance [32]. Conventional cerebral angiography is indicative of vasculitis in up to 75% if performed repeatedly [1,8,11,31].

CSF examinations disclose abnormal findings (cell count >5 cells/μl or total protein concentration >45 mg/dl) in the majority of patients [15]. Oligoclonal banding is found occasionally. Besides possible high CRP, serum screening is unremarkable for complement factors, ANA, ANCA or bacterial or viral antibodies. Although a large-scale ‘laboratory screen’ for autoimmune or infectious diseases is essential to exclude treatable differential diagnoses, one should be prepared for occasional ‘positive’ results.

Brain biopsy represents the gold standard in establishing the diagnosis in PACNS [9,16,26,33–35]. In PACNS, CNS biopsy specimens should be obtained in MRI-or angiographically involved areas [15]. Histopathological examination reveals a definite diagnosis of PACNS in approximately 60% of patients [8]. The ideal diagnostic brain biopsy is a 1-cm³ brain tissue with both grey and white matter as well as leptomeninges, and preferably a cortical vessel. The rate of false-negative brain biopsies is explained by the segmental involvement of vessels and a possible mismatch between radiological abnormalities and histological predominant lesions [8]. The morbidity rate of brain biopsy (0·03–2%) is definitely lower than the risks of unnecessary immunosuppressive treatments [8].

It is apparent that angiography and biopsy do not provide the same information in all patients [8]. Histology showed PACNS in 62% of Salvarini's patients who underwent biopsy [10]. Despite the fact that angiography has become the most frequent method of diagnosing PACNS, brain biopsy remains the gold standard [26]. It is important to realize that a negative biopsy certainly does not rule out the condition, and it should be considered as an attempt to establish the diagnosis and exclude other conditions [15]. A prospective multi-centre collaborative study collecting patients suspected to have cerebral vasculitis is needed urgently in order to establish standardized diagnostic and therapeutic procedures [1,9].

Behçet's disease is a multi-system, chronic-relapsing vasculitis affecting predominantly the venous system [8,30]. This rare disorder is more prevalent in Turkish patients and patients from the Far East. For oculo-mucocutaneous disease, the diagnostic criteria of the International Study Group for Behçet's disease include recurrent oral ulcerations with at least two of the following: recurrent genital ulceration, eye lesions (uveitis, cells in the vitreous on slit-lamp examination or retinal vasculitis), skin lesions (erythema nodosum) or a positive pathergy test result [8,15,36]. CNS manifestations (neuro-Behçet) occur in about 30% of patients after an average of 5 years [8,15,36]. Of these, 80% present parenchymal neuro-Behçet with frequent brainstem involvement (Fig. 4) [37]. Often, neuro-Behçet resembles multiple sclerosis [36].

Twenty per cent of patients with neuro-Behçet present with intracranial sinus or venous thrombosis with pseudotumour cerebri. In Behçet disease skin or brain biopsy is often expendable; however, exclusion of other causes of neurological symptoms is important [15,38].

Systemic large vessel vasculitides include Takayasu arteritis (age <50 years) and giant cell arteritis (GCA) or cranial arteritis (age >50 years) [15,30,33]. In GCA, the involvement of CNS arteries is very rare (<2%) [15].

Medium-sized vessels are affected in classical polyarteritis nodosa and the Kawasaki disease of childhood [11,30,33,39]. In classical polyarteritis nodosa, CNS involvement with headaches and encephalopathy is known in up to 20% [15].

The small vessel vasculitides are separated into immune complex-mediated [cryoglobulinaemic, immunoglobulin (Ig)A-associated, hypocomplementaemic anti-C1q] and ANCA-associated variants (microscopic polyangiitis, granulomatosis with polyangiitis Wegener and eosinophilic granulomatosis with polyangiitis Churg–Strauss) [11,30,33,39]. In these small vessel vasculitides, involvement of the peripheral nervous system is more common [15,40]; CNS involvement is rare (10% in granulomatosis with polyangiitis Wegener [15,41], 15% in eosinophilic granulomatosis with polyangiitis Churg–Strauss [15,42]).

Exclusion of differential diagnoses (Table 1)

Important differential diagnoses include RCVS [5,22,43,44], intracranial atherosclerosis [45], Moyamoya disease, autoimmune encephalopathies and infectious disorders such as varicella zoster virus (VZV) vasculopathies or endocarditis [29]. As the majority of these diseases resemble the MRI, digital subtraction angiography (DSA) and laboratory findings of angiitis, a biopsy of affected tissue is often necessary in order to prove the correct diagnosis. In systemic angiitis, biopsy may be performed from affected organs such as kidney, upper airways, muscle or peripheral nerves [46]. For PACNS, a cerebral and meningeal biopsy is the gold standard for diagnosis. Moreover, detailed anamnesis and diagnostic work-up often allow diagnosis of non-inflammatory vasculopathies such as Moyamoya disease [47], Fabry's disease [48–50], Sneddon's syndrome [6] and RCVS [22,43,51,52]. The most important differential diagnosis to CNS vasculitis is RCVS, which is characterized by thunderclap headache, watershed cerebral ischaemia, cortical subarachnoidal haemorrhages and angiography suggestive for ‘vasculitis’ (Table 2). However, RCVS is reversible within 12 weeks and is a non-inflammatory disease which should be treated by nimodipine. The misdiagnosis as CNS vasculitis with aggressive immunosuppressive treatment would be fatal.

In Fabry disease, recurrent strokes are sometimes associated with mild CSF pleocytosis and with systemic signs of inflammation, and a misdiagnosis as rheumatic disease or vasculitis is quite common [50]. Unfortunately, Moyamoya disease is also often misdiagnosed as vasculitis, although a Moyamoya pattern in angiography due to vasculitis is very uncommon [34]. A livedo racemosa in patients with cryptogenic stroke should lead to a detailed diagnostic work-up in order to differentiate inflammatory (polyarteritis nodosa, systemic lupus erythemadosus) from non-inflammatory vasopathies (Sneddon syndrome, Divry–van Bogaert syndrome, migraine) [6].