Incidence, characteristics, and outcomes for children hospitalized between April 1, 2009 and November 30, 2009 for neurological complications of 2009 pandemic H1N1 influenza infection were compared to those hospitalized with seasonal influenza, in a study at University of Utah, Salt Lake City, and University of North Carolina, Chapel Hill, NC. Of 303 children hospitalized with pandemic H1N1 influenza, 18 (5.9%) had neurological complications, 9 in each epidemic wave, April 1 to July 30 and August 1 to November 30, 2009. A trend toward increased severity of neurological complications occurred in the second wave of cases. Most of the patients had a pre-existing underlying medical (usually neurological) condition. H1N1 influenza was detected by PCR from upper respiratory secretions. LP was performed in 10 patients and none had pleocytosis or elevated protein; PCR of CSF was negative for influenza virus in 1 patient tested. Fifteen (83%) were treated with oseltamivir. In pandemic cases, neurological complications included seizures in 12 (67%), status epilepticus in 7 (39%), encephalopathy 9 (50%), focal neurological abnormalities 5 (28%), and aphasia in 6 (33%). EEG was abnormal in 8 (44%), and MRI abnormal in 3 (7%). Focal neurological abnormalities persisted in 22% at discharge. In comparison, among 234 seasonal influenza cases hospitalized 2004-2008, 16 had neurological complications, including seizures in 10 (63%), and status epilepticus in 6 (38%). EEG was abnormal in only 1 (6%) and MRI was normal. None had encephalopathy, aphasia, or focal neurological deficits. Patients were younger (mean age 2.4 years) than those with pandemic influenza (mean ages 7.3 and 5.6 years). [1]

COMMENT. Pandemic 2009 H1N1 influenza is associated with heightened neurological complications in children compared to seasonal influenza.

In a study of 345 children hospitalized with 2009 influenza A (H1N1) in California, 30 (8.7%) had CNS complications, including seizures (n=17), altered mental status/delirium (18), or both (12). Presentation with seizures (p=.01) or altered mental status (p<.001) was significantly associated with ICU admission or death. Eleven (37%) of the 30 had preexisting cerebral palsy/developmental delay or seizure disorder. Seventeen (57%) were admitted to the ICU. Median length of stay was 4 days. Of 8 fatal cases, 5 had comorbid neurological disorders, including 4 with cerebral palsy/developmental delay. [2]

In a study of 478 children with 2009 influenza A (H1N1) virus in Israel, 42 patients (8.8%) were admitted to the PICU, and 41 (8.6%) had seizures, mostly febrile. Patients with metabolic and neurological disorders were at highest risk for severe complications. [3]

Influenza A-induced acute autonomic neuropathy is reported in a 15-year-old girl who developed severe and persistent orthostatic hypotension with loss of consciousness on standing [4]. Removal of circulating autoantibodies with a single iv immunoglobulin dose (2g/kg) resulted in immediate recovery.