An atypical case of post-varicella stroke in a child presenting with hemichorea followed by late-onset inflammatory focal cerebral arteriopathy

Post-varicella arterial ischemic stroke (AIS) is a rare but serious complication of varicella zoster virus (VZV) infection, with an estimated incidence of 1/15,000 children per year, and high risk of lifelong disability and increased mortality (1). Both in children and adults, the clinical diagnosis is based on neurological symptoms and signs due to AIS associated with a history of chickenpox or herpes zoster infection during the previous year, once other major causes for AIS are excluded (2-4). Of note, this diagnosis is often challenging since previous VZV rash may be absent in 30% of patients (5,6). Moreover, VZV DNA in cerebrospinal fluid (CSF) is positive in only 30% of subjects with VZV stroke, underlying that a negative PCR result does not exclude this diagnosis (5). The detection of anti-VZV IgG antibody in the CSF is the most sensitive diagnostic test, particularly when combined with demonstration of intrathecal synthesis (5-7). Qualitatively, the serum/CSF ratio of anti-VZV IgG antibody is compared with the serum/CSF ratio of albumin and total IgG, with a reduction of the former compared with the latter representing a positive result (8,9). A more quantitative assessment of intrathecal synthesis, the antibody index, has been described by Reiber and Lange: (CSF VZV IgG/serum VZV IgG)/(CSF total IgG or albumin/serum total IgG or albumin). An antibody index ≥1.5 is considered as positive (8). The underlying mechanism of VZV-associated AIS is not entirely clarified. Viral markers have been identified in patients’ CSF as well as viral DNA, antigens and particles in the wall of affected arteries (7). These findings support the hypothesis of a direct VZV arterial infection associated with variable indirect inflammatory responses (6), after transaxonal viral migration from the cranial nerve ganglia to the cerebral arterial walls (2). Indeed, inflammatory focal cerebral arteriopathy is the most common cerebrovascular manifestation attributed to VZV (10), classically involving the proximal middle cerebral artery (MCA) and/or other medium-sized vessels such as the terminal internal carotid Letter to the Editor