ABSTRACT Background: Susac syndrome is characterized by the triad of branch retinal arterial occlusions, encephalopathy and cochlear microangiopathy. The underlying process is believed to be a small vessel vasculitis causing microinfarcts in the retina, brain and cochlea. Methods: Analysis of two male and two female cases of Susac syndrome recognized in Australia. Results: In this series the epidemiology, mode of presenta- tion, ophthalmologic features, neurologic and cochleo- vestibular features, radiologic characteristics, cerebrospinal fluid findings, therapeutic interventions, clinical course and outcome of Susac syndrome is examined. Key ophthalmo- logic differential diagnoses include systemic lupus erythe- matosis (SLE), Behçet’s syndrome and other vasculitides such as sarcoidosis, tuberculosis, syphilis and lymphoma. Neuro-otologic features are most frequently misdiagnosed as multiple sclerosis. Conclusion: Susac syndrome, first described in 1979, is becoming an increasingly recognized condition. Early recog- nition of the syndrome is important because treatment with systemic immunosuppression may minimize perma- nent cognitive, audiologic and visual sequelae. Key words: branch retinal artery occlusion, encephalopathy, hearing loss, Susac syndrome, tinnitus, vasculitis. INTRODUCTION The triad of branch retinal arteriolar occlusions, encepha- lopathy and cochlear microangiopathy was first described by Susac et al. in 1979, 1 although patients with one or two elements of the triad had been described previously. 2,3 The aetiology remains unknown; however, it is thought to be an autoimmune vasculitis affecting peripheral branch retinal arterioles, arterioles supplying the apical turn of the cochlea and vestibular labyrinth, and small vessels of the brain. Approximately 60 cases have been described in published reports including our four cases. 4–6 CASE 1 A 29-year-old male investment analyst presented in January 1995 with a 10-week history of intermittent visual blurring, headaches, left-sided paraesthaesiae, olfactory auras and confusion. Fluctuating attention and concentration, higher level language difficulties and moderate psychomotor slowing were demonstrated on neuropsychological testing. Neurological examination revealed an unsteady gait but was otherwise normal with flexor plantar responses. Complex partial seizures were suspected and he was started on sodium valproate. Computed tomography (CT) of the brain was normal. Magnetic resonance imaging (MRI) demonstrated multiple hyperintense white and grey matter lesions on T2 weighted images with predominant involvement of central grey matter (Fig. 1). An electroencephalogram (EEG) showed widespread triphasic waves consistent with encephal- opathy but no epileptiform patterns. Visual evoked responses were normal while somatosensory evoked poten- tials showed a mild delay in cortical latencies. Cerebrospinal fluid (CSF) protein levels were markedly elevated at 2.0 g/L (0–0.45 g/L) with negative oligoclonal immunoglobulin bands. Full blood count, erythrocyte sedimentation ratio, C-reactive protein, serum antinuclear antibody, rheumatoid factor, antineutrophil cytoplasmic antibody, antiphospho- lipid antibody and HIV serology were normal or negative. Clinical and Experimental Ophthalmology (2000) 28, 373–381 Original Article Susac syndrome: microangiopathy of the retina, cochlea and brain Valerie PJ Saw MBBS, 1 Paul A Canty FRACS, 2 Catherine M Green MBChB, 3 Robert J Briggs FRACS, 2 Phillip D Cremer FRACP, 4 Brian Harrisberg FRACO, 1 Peter McCluskey FRACO, 1,5 Justin O’Day FRACO, 3 Mark Paine FRACP, 2,3,6 Denis Wakefield FRACP FRCPA 7 and John DG Watson FRACP 4 1 Department of Ophthalmology, Royal Prince Alfred Hospital, Sydney, 2 Department of Otolaryngology, 3 Department of Ophthalmology, Royal Victoria Eye and Ear Hospital, Melbourne, 4 Department of Neurology, Department of Medicine, University of Sydney, Royal Prince Alfred Hospital, Sydney, 5 Department of Ophthalmology, 6 Department of Neurology, St Vincent’s Hospital, Melbourne, 7 School of Pathology, University of New South Wales, Sydney, Australia. ■ Correspondence: Dr Valerie Saw, 28 Strathfield Avenue, Strathfield, NSW 2135, Australia. Email: valsaw@bigpond.com.au