In patients with dementia, the clinical presentation of unrelated medical conditions may be concealed or atypical, and symptoms difficult to interpret, or confounded by existing cognitive deterioration or by medications. These difficulties pose an extraordinary challenge to clinicians, and may contribute to the disturbing evidence of inadequate assessment and treatment of medical conditions in patients with dementia. Here, we report the case of an 82-year old woman diagnosed with Alzheimer's disease, whose MMSE score started to deteriorate rapidly after six years of steady decline as a result of a temporal arteritis. Temporal arteritis, a diagnosis which is often made several months after the onset of symptoms even in the general population, can be difficult to identify in patients with pre-existing dementia.