Herpes zoster preceding neuromyelitis optica spectrum disorder: casual or causal relationship? A systematic literature review

: Neuromyelitis optica spectrum disorder (NMOSD) is a severe, inflammatory, immune-mediated astrocytopathy of the central nervous system, characterized by recurrent inflammatory events primarily involving optic nerves and the spinal cord. Recently, a triggering role of infectious events in the development of NMOSD has been suggested. Varicella zoster virus (VZV) is the agent most involved, although the linkage with anti-aquaporin-4 antibodies is so far unknown. A review of the literature on the association between NMOSD and VZV infection was carried out by searching PUBMED and EMBASE from 1975 to July 2020. A total of 13 articles concerning Herpes zoster preceding NMOSD were identified. All patients were female and the median age at NMOSD presentation was 28.5 (range 5-63) years. Four NMOSD cases occurred after chicken pox while the remaining ten after HZ. Full recovery occurred in 5/14 patients. From the review of the literature, we can infer that VZV seems to trigger LETM attacks and not the disease itself. The strict temporal relationship between VZV infection and NMOSD seems to exceed the pure chance and represents an unusual clinical scenario posing several diagnostic and management challenges.