Abstract Background/Aims Giant-cell arteritis (GCA) is a large vessel vasculitis predominantly affecting those above 50 years of age. Creutzfeldt-Jacob disease (CJD) is not a well-recognised differential diagnosis of GCA presentation. Prion diseases are progressive, currently untreatable and ultimately fatal. Methods We report the case of a 76-year-old female who had an eventful hospital stay of 37 days. She has a history of asthma, hypertension, ulcerative colitis and right-sided GCA 5 years back (normal inflammatory markers & biopsy). Results The patient presents to Harlow ED with a right temporal headache with tenderness, jaw claudication symptoms, blurred vision, diplopia, dizziness and painful right eye movements. Her CRP was <1 and ESR was 5. The plan was to treat it as a recurrence of her GCA and to continue with the high dose Prednisolone started by the ED. CT Head was normal. Owing to poor response, IV Methyl Pred was given. On day six, patient was re-admitted with worsening headache and generalised decline. Ophthalmology review noted multiple visual field defects and treated as GCA. A neurology review noted the patient to be encephalopathic. Advice was for MRI head and CSF analysis - both NAD. On day 12 she had ongoing headache, diplopia, poor vision/memory, and reduced hearing in right ear, but alert and following instructions. On day 17, ENT suggestion was to treat as Meniere’s and start on Betahistine. On day 22, the patient had a TIA episode and discussed with Stroke team. Repeat CT Head was nil acute. By day 26, the patient was unresponsive intermittently and was treated as hypoactive delirium. On day 31 a seizure activity was noticed. Neurology review on day 33 noted rapid decline- the patient being mute, seizure/atypical encephalitis. MRI-Head with contrast showed the possibility of CJD. The very next day patient was reviewed by the team from National CJD Research and Surveillance team, Edinburgh. The formal diagnosis given was: probable Sporadic CJD (visual/Heidanhain variant), rapidly progressive cognitive decline with visual signs, myoclonus, and akinetic mutism, positive MRIs, bland CSF, no clear iatrogenic or variant risk factors, and no credible alternative diagnosis. The distressed family members were updated and the patient was put on EoL pathway. She died peacefully four days later (Day 37). Conclusion The importance of this case is the conflicting inputs from at least five specialities in a rapidly deteriorating patient. A background of previous right-sided GCA did prompt initial treatment in those lines. MRI Head DWI sequence did show the classic ‘cortical ribboning’ with right caudate and lentiform hyperintensity; which clinched the mysterious diagnosis of this rare disease which requires public health surveillance. CJD is to be suspected in any undiagnosed rapidly progressive mental deterioration or dementia, often with behavioural abnormalities and myoclonus. Disclosure S. Narikkoottungal: None. K. Gunasekera: None. K. Ahmed: None.