Background Susac's syndrome is described as a triad of encephalopathy, retinopathy, and hearing loss. We describe a case where fluorescein angiography was required to demonstrate the retinopathy which was not detectable by indirect opthalmoscopy.

Case Report A 22 year old lady presented on the background of two admissions to hospital for abdominal pain, nausea and vomiting over the preceding 8 months. The presentation to neurology was precipitated by further episodes of nausea and vomiting accompanied by agitated and sometimes bizarre behaviour, including a delusion of living in a foreign country. On examination she was encephalopathic with a score on the revised Addenbrookes cognitive examination (ACE–R) of 66/100, with particular deficit on attention, memory, and verbal fluency. Visual fields to confrontation and colour vision were normal. Visual acuity was 6/18 (right) and 6/9 (left). Retinal vasculature appeared normal on indirect opthalmoscopy. She had a mild upper motor neuron left sided facial weakness. In her limbs there was normal tone, power, and reflexes, but plantar responses were extensor bilaterally. CSF results at presentation were: White cell count=16/cc, protein=1.88 g/dl, glucose=normal, CSF angiontensive converting enzyme (ACE) =normal, lactate=normal, viral PCR including JC virus=normal. There was a polyclonal increase in CSF gamma globulin. MRI of brain showed a number of T2 white matter hyperintensitiesaffecting the deep white matter, periventricular regions, and genu and splenium of the corpus callosum. VERS showed delayed P100 responses bilaterally. FBC showed an eosinophilia (1.8×10.9). The following investigations were normal: vitamin B12, folate, blood film,urine toxicology, U&Es, LFTS, CRP, ammonia, protein electrophoresis, plasma and urine total porphyrins, serum ACE, bartonella serology, VGKC, NMDA and antineuronal antibodies, C3/4, ANA, ANCA, HIV serology, ECG, and CT angiogram of intracranial vessels. On transfer to neurology, i.v. methylprednisolone was administered for 5 days to cover for the possibility of acute disseminated encephalomyelitis (ADEM), pending further investigation for Susac's Syndrome. This led to some clinical improvement (ACE–R=77/100) and the CSF protein diminishing (0.64 g/dl). Fluorescein angiography subsequently showed bilateral arteritis with occlusion in left eye on the same day as a normal opthalmoscopy. We concluded that the patient had a form fruste of Susac's Syndrome and follow up in November 2012 highlighted ongoing emotional lability but no symptoms of cognitive deficit and improved MRI appearances with maintenance prednislone. Her mother revealed she had heard of the condition in the newspaper.

Conclusions In cases of suspected Susac's syndrome, normally appearing retinal vessels on fundoscopy do not exclude retinal arteritis, especially when peripherally distributed, and a fluorescein angiogram should be requested. Although this has been recognised in the ophthalmic literature1, it is important for neurologists consider requesting the test despite normal fundoscopy. In addition, audiogram may be normal in form fruste presentations which may also include psychiatric features and migraine. Clinicians should not be dissuaded from considering Susac's if not all features of the classic triad are present.