"Limbic encephalitis with acute onset and Hu antibodies treated with rituximab: Paraneoplastic or non-paraneoplastic disorder?"

Paraneoplastic limbic encephalitis (PLE) associated with Hu antibodies is a rare autoimmune disorder usually characterized by subacute onset of slowly progressive neurocognitive symptoms. Small cell lung carcinoma is the most frequent PLE-associated cancer, which negatively affects the prognosis of the disease. We report on a patient with acute onset of confusional state and disorganized speech. Cerebrospinal fluid analysis and brain MRI temporal lesions corroborated the diagnostic suspects toward infectious or autoimmune encephalitis but testing for onconeural antibodies suggested the alternative diagnosis of PLE, in the absence of cancer (total-body CT and PET were negative). The patient's serum was positive for Hu antibodies, thus leading to a diagnosis of PLE. First-line immunotherapies were ineffective on the neurocognitive symptoms, which improved after rituximab. Six months later, a retropharyngeal peri-jugular mass was histopathologically diagnosed as a metastasis of lung neuroendocrine tumor. Still clinically improved, the patient died from the oncological disease-related complications. Testing for onconeural antibodies should be considered in patients with clinico-radiological features of acute infectious or autoimmune encephalitis.

Diffusion-weighted imaging in patients with progressive multifocal leukoencephalopathy.

Progressive multifocal leukoencephalopathy (PML) is a severe demyelinating disease of the central nervous system due to JC polyoma virus infection of oligodendrocytes. PML develops in patients with impaired T-cell function as occurs in HIV, malignancy or immunosuppressive drugs users. Until now no imaging methods have been reported to correlate with clinical status. Diffusion-weighted imaging (DWI) is a robust MRI tool in investigating white matter architecture and diseases. The aim of our work was to assess diffusion abnormalities in focal white matter lesions in patients with PML and to correlate the lesion load measured with conventional MRI and DWI to clinical variables. We evaluated eight patients with a biopsy or laboratory-supported diagnosis of PML. All patients underwent MRI including conventional sequences (fluid attenuated inversion recovery-FLAIR) and DWI. Mean diffusivity (MD) maps were used to quantify diffusion on white matter lesions. Global lesion load was calculated by manually tracing lesions on FLAIR images, while total, central core and peripheral lesion loads were calculated by manually tracing lesions on DWI images. Lesion load obtained with the conventional or DWI-based methods were correlated with clinical variables such as disease duration, disease severity and survival. White matter focal lesions are characterized by a central core with low signal on DWI images and high MD (1.853 x 10(-3) mm2/s), surrounded by a rim of high signal intensity on DWI and lower MD (1.1 x 10(-3) mm2/s). The MD value of normal-appearing white matter is higher although not statistically significant (0.783 x 10(-3) mm2/s) with respect to control subjects (0.750 x 10(-3) mm2/s). Inter-rater correlations of global lesion load between FLAIR (3.96%) and DWI (3.43%) was excellent (ICC=0.87). Global lesion load on FLAIR and DWI correlates with disease duration and severity (respectively, p=0.037, p=0.0272 with Karnofsky scale and p=0.0338 with EDSS on FLAIR images; p=0.043, p=0.0296 with Karnofsky scale and p=0.0365 with EDSS on DW images). Central core lesion load on DWI correlates with disease duration and severity (respectively p=0.043, p=0.0103 with Karnofsky scale and p=0.0112 with EDSS), while peripheral lesion load does not correlate with any clinical variable. The global lesion load in PML correlates with disease duration and severity. DWI images, which can distinguish within lesions a central core from a peripheral rim, reveal that a larger central core component correlates to a worsened clinical status and longer disease duration. On the other hand the peripheral rim lesion load visualized on DWI images does not correlate with clinical variables and does not achieve obtaining further prognostic information with respect to conventional imaging.