Mass Confusion

Her family history of lung cancer and her smoking increases the possibility of paraneoplastic encephalitis, which often has subacute behavioral changes that precede complete neurologic impairment. Inflammatory or hemorrhagic CSF is seen with Balamuthia amoebic infection, which causes a granulomatous encephalitis and is characteristically associated with a mass lesion. Toxoplasmosis causes encephalitis that can be profound, but patients are usually immunocompromised and there are typically multiple lesions.

Laboratory results showed a normal white blood cell count and differential, basic metabolic profile and liver function tests, and C-reactive protein. Human immunodeficiency virus antibody testing was negative. Chest radiography and computed tomography of chest, abdomen, and pelvis were normal. A repeat MRI of the brain with contrast was reported as showing a 2.4 x 2.3 x 1.9 cm heterogeneously enhancing mass in the right frontal lobe with an enhancing dural tail and underlying hyperostosis consistent with a meningioma, and blooming within the mass consistent with prior hemorrhage. No mass effect was present.

The meningioma was resected 3 days after admission but her symptoms did not improve. Routine postoperative MRI was reported to show expected postsurgical changes but no infarct. Brain biopsy at the time of the operation was reported as meningioma and mild gliosis without encephalitis.

The reported MRI findings showing unchanged size and overall appearance of the mass, its connection to the dura and skull, and the pathology results all suggest that the mass is a meningioma. There is no evidence of disease outside of the CNS. Some cancers that provoke a paraneoplastic response can be quite small yet may incite an immune encephalitis; anti-NMDAR-mediated encephalitis can occur with malignancy (often ovarian), although it also arises in the absence of any tumor. Any inclination to definitively exclude conditions not seen on the brain biopsy must be tempered by the limited sensitivity of brain histology examination. Still, what was not seen warrants mention: vascular inflammation suggestive of CNS vasculitis, granulomas that might point to neurosarcoidosis, malignant cells of an infiltrating lymphoma or glioma, or inflammatory cells suggestive of encephalitis. Prion encephalopathy remains possible.

The patient remained unresponsive. A repeat EEG showed bilateral generalized periodic epileptiform discharges with accompanying twitching of the head, face, and left arm, which were suppressed with intravenous propofol and levetiracetam. Three weeks following meningioma resection, a new MRI was read as showing new abnormal signal in the right basal ganglia, abnormality of the cortex on the diffusion weighted images, and progressive generalized volume loss.

Among the aforementioned diagnoses, focal or diffuse periodic epileptiform discharges at 1-2 hertz are most characteristic of prion disease. Striatal and cortical transverse relaxation time (T2)-weighted and diffusion-weighted imaging (DWI) hyperintensities with corresponding restricted diffusion is characteristic of Creutzfeldt-Jakob disease (CJD), although metabolic disorders, seizures, and encephalitis can very rarely show similar MRI findings. The clinical course, the MRI and EEG findings, and nondiagnostic biopsy results, which were initially not assessed for prion disease, collectively point to prion disease. Detection of abnormal prion protein in the brain tissue by immunohistochemistry or molecular methods would confirm the diagnosis.

Review of the original right frontal cortex biopsy specimen at the National Prion Disease Pathology Surveillance Center, including immunostaining with 3F4, a monoclonal antibody to the prion protein, revealed granular deposits typical of prion disease. This finding established a diagnosis of prion disease, likely sporadic CJD. The patient was transitioned to palliative care and died shortly thereafter.

Brain autopsy showed regions with transcortical vacuolation (spongiform change), other cortical regions with varying degrees of vacuolation, abundant reactive astrocytes, paucity of neurons, and dark shrunken neurons. Vacuolation and gliosis were observed in the striatum and were most pronounced in the thalamus. There was no evidence of an inflammatory infiltrate or a neoplastic process. These findings with the positive 3F4 immunohistochemistry and positive Western blot from brain autopsy, as well as the absence of a mutation in the prion protein gene, were diagnostic for CJD.

An investigation was initiated to track the nondisposable surgical instruments used in the meningioma resection that may have been subsequently used in other patients. It was determined that 52 neurosurgical patients may have been exposed to prion-contaminated instruments. The instruments were subsequently processed specifically for prion decontamination. After 7 years, no cases of CJD have been diagnosed in the potentially exposed patients.

CJD is a rare neurodegenerative condition¹ classified as one of the transmissible spongiform encephalopathies, so called because of the characteristic spongiform pattern (vacuolation) seen on histology, as well as the presence of neuronal loss, reactive gliosis in the gray matter, and the accumulation of the abnormal isoform of the cellular prion protein.² It affects about one person in every one million people per year worldwide; in the United States there are about 300 cases per year. The most common form of human prion disease, sporadic CJD, is relentlessly progressive and invariably fatal, and in most cases, death occurs less than 5 months from onset.³ There is no cure, although temporizing treatments for symptoms can be helpful.