Case Presentation: A 69-year-old male with prostate cancer in remission developed diplopia 2 weeks prior to presentation. Workup at the referring hospital included a normal ophthalmologic exam and an MRI brain with possible mastoiditis and/or otitis media. A course of unknown oral antibiotics was completed. He had no improvement of his diplopia and progressed to have hypersomnia, confusion, agitation, and inappropriate laughter, leading to his admission here. On arrival here, he had fluctuating levels of alertness and orientation, voicing nonsensical statements. He had no nuchal rigidity and no signs of mastoiditis or otitis media. Cranial nerve exam was normal with extraocular movements intact. He had right arm neglect with myoclonic jerks in both arms and an upgoing plantar response bilaterally. Strength, sensation, and other reflex testing were normal. A complete blood count and complete metabolic panel, prostate-specific antigen and c-reactive protein values were normal. Cerebrospinal fluid (CSF) had normal cell counts, protein, and glucose. CSF gram stain, culture, PCR panel, and CSF autoimmune and paraneoplastic panels were negative. 24-hour video EEG had no seizures or sharp wave complexes. CSF 14:3:3 results were inconclusive. Repeat MRI showed high signal intensity in bilateral cortices only. CSF real-time quaking-induced conversion (RT-QuIC) testing was positive and he met criteria for probable sporadic Creutzfeldt–Jakob disease (CJD). He developed diffuse hypertonia and mutism and died less than one month after admission. An autopsy was declined.

Discussion: Altered mental status is commonly seen in the hospital; CJD is rare but must be considered in the appropriate clinical picture given its grim prognosis. In the absence of an alternative diagnosis, probable criteria can be reached with a rapidly progressive dementia with 2 of 4 clinical features (myoclonus, visual/cerebellar signs, pyramidal/extrapyramidal signs, or akinetic mutism) along with one positive test, including periodic sharp wave complexes on EEG, a positive 14-3-3 CSF assay or MRI with high signal in the caudate/putamen or in at least 2 cortical regions. A neuropsychiatric disorder in addition to a positive CSF RT-QuIC also meets probable diagnostic criteria. The RT-QuIC test assesses the ability for the prion protein in the CSF of a patient with CJD to induce misfolding of normal proteins and has a sensitivity of 92% and a specificity up to 100%. The definitive diagnosis of CJD is made via brain tissue pathology. Our case met both probable diagnostic criteria and had negative testing for viral, autoimmune, and paraneoplastic testing for an alternative diagnosis, so a brain biopsy was deferred.

Conclusions: It is important to understand the general diagnostic criteria for CJD to ensure this rare diagnosis is not missed. The RT-QuIC test is a newer, specific test that can be very helpful to make a less invasive probable diagnosis of CJD.