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Neurological involvement is one of the most devastating manifestations of Behçet's disease.1 However, the pathogenic mechanism for CNS lesions in patients with neuro-Behçet's disease is unclear. Although vasculitis is usually considered to be the central pathological feature in Behçet's disease, a vasculitic process was not usually demonstrated in the CNS.2
Diffusion weighted imaging can detect changes in water diffusion associated with cellular dysfunction. It has been well documented that acute infarction related to cytotoxic oedema is characterised by a marked decrease in diffusion, and also that increased interstitial water related to vasogenic oedema shows increased diffusion.3 Conventional MRI cannot distinguish between these different types of oedema. We report on a patient with neuro-Behçet's disease with a significantly reversible T2 signal and diffusion abnormalities in CNS lesions.
A 54 year old Asian man was admitted with dysarthria and left hemiparesis, which evolved over a period of 2 days and was associated with gradual mental deterioration. The patient had a history of frequent orogenital ulcers and acneiform nodules on his face. Physical examination showed active genital ulceration. Neurological examination disclosed drowsy consciousness and disorientation. Moderate degrees of hemiparesis and hemihypaesthesia involving the face, arm, and leg were found on the left side. Deep tendon reflexes were increased and Babinski's sign was extensor on the left side. Erythrocyte sedimentation rate (54 mm/h) and C-reactive protein concentration (3.4 mg/100 ml) were increased. Examination of CSF showed mild pleocytosis (18 white blood cells/mm3) with normal concentrations of protein and glucose. Fundus examination showed retinal vein occlusion and retinal haemorrhage on the right side. The diagnosis of Behçet's disease was made based on the recurrent orogenital ulcerations, skin lesions, and eye involvement.
The patient was examined on a 1.5T MR unit (Signa Horizon, Echospeed; General Electric Medical Systems) with echoplanar imaging (EPI) capability. Fast spin echo, T2 weighted images (T2 weighted images; TR/TE 4200/112 ms; field of view 21×21 cm; matrix 256×192; and slice thickness 5 mm) were obtained. Diffusion weighted imaging was obtained in the transverse plane using a single shot EPI (TR/TE 6500/125 ms; field of view 24×24 cm; matrix 128×128; slice thickness 5 mm; and two b values 0 and 1000 s/mm2). The diffusion gradients were applied along the three axes (x, y, z) simultaneously. The apparent diffusion coefficient (ADC) was calculated based on the negative slope of the linear regression line best fitting the points for b versus ln(SI); where SI is the signal intensity from a region of interest within the images acquired at each b value. Performing this calculation on a pixel by pixel basis created the ADC maps.
Brain MRI performed 3 days after symptom onset showed extensive T2 hyperintensities involving the corona radiata, internal capsule, basal ganglion, thalamus, and midbrain on the right side. Brain diffusion weighted imaging showed slight hyperintensities which were limited to the corona radiata, the medial portion of the basal ganglion, and the thalamus. Four sampled ADCs in the corresponding regions of T2 hyperintensity demonstrated increased diffusion (ranging from 1.17 to 1.26×10-5 cm2/s), compared with a matching location in the uninvolved contralateral hemisphere (ranging from 0.77 to 0.80×10-5 cm2/s, figure A and B). Magnetic resonance angiography showed no abnormalities. The patient improved rapidly after treatment with a high dose of corticosteroid. Within 2 weeks all previously noted neurological abnormalities had resolved except for a slight left hemiparesis. An MRI repeated at this time showed a partial decrease in the extent of the T2 hyperintensity. One year later he was readmitted with a slowly progressive bulbar weakness, frontal lobe dysfunction, urinary incontinence, and depressive mood changes. Follow up MRI performed at this time, showed that the previous T2 abnormalities had improved, but the atrophy of the brain stem and basal ganglia became evident with periventricular high signal intensities. Four ADCs sampled in locations corresponding to those of the initially increased ADCs decreased to values which ranged from 0.98 to 1.07×10-5 cm2/s (figure C and D).
In our patient the ADC maps and ADC values showed high proton mobility, which suggests vasogenic oedema in acute lesions of neuro-Behçet's disease. Vasogenic oedema develops when the blood-brain barrier is disrupted and is not primarily associated with cellular damage. Discrimination between cytotoxic and vasogenic oedema has important clinical implications because vasogenic oedema can be reversed by proper management.
According to the MRI findings for neuro-Behçet's disease, the most prevalent abnormalities are located in the brain stem or the basal ganglia extending to the diencephalic structures during an acute attack, and brainstem atrophy in chronic cases.4 The reversibility of CT or MRI abnormalities of acute lesions in neuro-Behçet's disease has also been documented and correlated with clinical improvement.4 5 The serial MRI findings in our patient were consistent with those described in previous reports. The precise pathomechanism of CNS lesions in Behçet's disease has not been established. Studies of pathology showed that lymphocytic or neutrophilic meningoencephalitis with perivascular inflammatory cell cuffing around venules and capillaries were predominant in the brain stem and basal ganglia in neuro-Behçet's disease.1However, most studies showed histopathological changes at a chronic stage of the disease and histopathological findings may show various types of lesions according to the age of lesion at the time of examination. A recent pathological report in a fulminant form of neuro-Behçet's disease found no evidence of vasculitis but an acute destructive inflammatory process.2 It has been postulated that at an early stage of the disease, the reversibility of lesions may reflect a reversible breakdown in the blood-brain barrier rather than gliosis or infarction.5 The pattern of diffusion changes in the acute lesions in our patient strongly supports the idea that there is increased permeability in the blood-brain barrier as a result of the primary inflammatory process.
We thank Byung Kee Yoo for his assistance with diffusion weighted MR data acquisition.
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