Sporadic Creutzfeldt-Jakob disease (sCJD) is the most common form of prion diseases. Although almost 100 years have passed since this disease was first described, specific treatment still does not exist. The case is presented of a 57-year-old woman, initially diagnosed with ischemic stroke. On the day of admission to hospital she presented non-specific symptoms (speech disorders, visual disturbances). During hospitalization, the patient presented rapidly progressive dementia. Later, new symptoms, such as blindness, akinetic mutism, rigidity and myoclonus appeared. With the progression of the disease, the patient developed characteristic MRI and EEG changes for sCJD. After excluding other potential causes, the diagnosis of probable sCJD was made. However, the result of 14-3-3 protein in the cerebrospinal fluid (CSF), characteristic for CJD,was negative. This case report highlights the importance and difficulties in differential diagnosis of rapidly deteriorating cognitive function disorder.