DIFFUSION TENSOR IMAGING DEMONSTRATES FIBER IMPAIRMENT IN SUSAC SYNDROME

Abstract

Susac syndrome is a rare disease, characterized by the triad of hearing loss, branch retinal artery occlusions, and encephalopathy with predominantly cognitive and psychiatric symptoms.1,2 Focal ischemic lesions in the corpus callosum detectable by conventional MRI are a typical feature of Susac syndrome.3,4 The lesions detectable by conventional MRI do not, however, explain the type and severity of the neuropsychological deficits.5,6 In this study, we tested the hypothesis of whether widespread tissue damage of the otherwise normal-appearing white matter (NAWM) could be detected in patients with Susac syndrome using diffusion tensor imaging (DTI).7 DTI is a noninvasive technique for detection of macro- and microstructural impairment of fiber integrity on the basis of normal values for the fractional anisotropy (FA).8 We hypothesized that the neuropsychological symptoms in patients with Susac syndrome correlated well with the FA aberrations detected with DTI. ### Methods. We investigated four patients with clinically diagnosed Susac syndrome. Their encephalopathic symptoms varied from mild cognitive impairment to severe acute psychosis. The symptoms were dyscalculia, impaired memory, hallucinations, paranoia, disorientation, emotional indifference, and strongly reduced alertness, motivation, concentration and cognitive flexibility. Diagnosis of Susac syndrome was established by the documentation of branch retinal artery occlusions, sensorineural hearing loss, encephalopathy, and the characteristic multifocal snowball-like hyperintense lesions on T2-weighted images (figure 1). In all patients, the diagnosis was based on the typical clinical triad, supported by the detection of the typical white matter (WM) lesions on T2-weighted MRI. Figure 1 T2-weighted images illustrating “snowball” lesions in the corpus callosum of Patients 1 through 4 (A) Patient 1 showed a lesion in the genu of the corpus callosum. (B) “Snowball” lesion in the splenium of the corpus callosum of Patient 2. (C) Patient 3 showed multiple lesions along the corpus callosum. (D) Lesion in the splenium of Patient …