Neurological Complications and Viral Myositis in Pediatric Patients with Influenza Infection Attending a Tertiary Hospital in Madrid

Background: Influenza infection in children may be associated with neurological complications, including seizures and encephalitis, as well as suspected acute viral myositis, which may result in significant morbidity. Objective: This study aimed to estimate the incidence of neurological complications and suspected acute viral myositis in pediatric patients with laboratory-confirmed influenza and explore clinical and epidemiological characteristics potentially associated with these complications. Methods: A retrospective observational study was conducted including children aged 0–18 years with laboratory-confirmed influenza A or B who attended a tertiary hospital in Madrid between 2017 and 2023. Neurological complications were defined as seizures or encephalitis during the influenza episode. Incidence of complications and hospital admissions was analyzed across epidemiological periods (pre-pandemic, pandemic, and post-pandemic). Results: A total of 617 influenza episodes were identified. Neurological complications occurred in 33 patients (5.3%) and suspected acute viral myositis in 23 (3.7%). Seizures were the most frequent neurological manifestation (66.7%). Underlying neurological disease was strongly associated with neurological complications (31.6% vs. 3.6%; p < 0.01). Myositis was more frequent in influenza B infection (7.3% vs. 1.8%; p < 0.01). The frequency of neurological complications and suspected acute viral myositis did not differ significantly across epidemiological periods. Conclusions: Neurological complications and myositis were uncommon in pediatric influenza. Pre-existing neurological diseases were strongly associated with neurological complications.