CADASIL progression after neurologic infectious insults: Case report of a new pathogenic NOTCH3 mutation

Cerebral autosomal dominant arteriopathy with subcortical infarcts (CADASIL) is the most common monogenic inherited small vessel disease. Autoimmune disorders, including multiple sclerosis, have been documented to co-exist with CADASIL, which can complicate the initial recognition. Inflammatory insults have been suggested to be associated with disease progression with SARS-CoV-2 infection. We present a case of a white woman in her 50s who demonstrated progressive white matter changes with initial demyelinating characteristics in 2010. Their course was notable for accelerated progression after multiple central nervous system insults, including herpes simplex virus (HSV) encephalitis in 2017, suspected post-infectious autoimmune encephalitis in 2018, and neuroinvasive West Nile virus (WNV) infection with confirmed para-infectious NMDA receptor encephalitis in 2022. CADASIL was suspected given confluent anterior temporal and external capsule white matter changes. She was found to have a novel NOTCH3 missense mutation in exon 3 (c.313T>C, p.(Ser105Pro)), and electron microscopy of a skin biopsy demonstrated granular osmiophilic material deposits diagnostic of CADASIL. This case demonstrates a novel pathogenic NOTCH3 mutation as well as the complexity of CADASIL diagnosis in the setting of possible concomitant demyelinating disease and other central nervous system insults. Significant phenotypic variability and overlapping acquired pathologies can make CADASIL recognition difficult. Given precipitous decline with each central nervous system insult in this case, we suspect these events hastened CADASIL progression.