224. Charles bonnet syndrome caused by optic neuritis following immune desensitisation therapy for allergic rhinitis

A 42 year old man developed peri-orbital headache and pain on eye movements followed by progressive left monocular blindness. Five days later he developed various visual hallucinations which were both unformed and formed. The patient retained insight and had no symptoms suggestive of psychiatric illness. The hallucinations settled after several days as his visual deterioration reached its nadir. The patient had recently received four weekly injections of grass and olive tree extracts for the treatment of allergic rhinitis as part of an immune desensitisation protocol. Right visual acuity was normal with reduced colour saturation, though acuity was perception of hand movements only on the left. Fundoscopy revealed bilateral optic disc swelling but the remainder of the neurological examination was normal. Magnetic imaging revealed marked oedema and enhancement of the left optic nerve, in association with punctate T2 and FLAIR hyperintensities throughout the subcortical white matter bilaterally. Investigations for systemic vasculitis, antiphospholipid antibody syndrome, sarcoidosis and neuromyelitis optica (aquaporin-4) were negative. Given the clinical and radiological features a diagnosis of acute disseminated encephalomyelitis (ADEM) was made. To our knowledge this is the first reported case of Charles Bonnet syndrome in ADEM. The potential relationship between the illness and recent immune desensitisation therapy is discussed with reference to the literature.