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Volume 16, Number 1—January 2010


Acute Encephalopathy Associated with Influenza A Infection in Adults

Nelson LeeComments to Author , Chun Kwok Wong, Paul K.S. Chan, Niklas Lindegardh, Nicholas J. White, Frederick G. Hayden, Edward H.C. Wong, Ka Shing Wong, Clive S. Cockram, Joseph J.Y. Sung, and David S.C. Hui
Author affiliations: The Chinese University of Hong Kong, Hong Kong Special Administrative Region, People’s Republic of China (N. Lee, C.K. Wong, P.K.S. Chan, E. Wong, K.S. Wong, C.S. Cockram, J.J.Y. Sung, D.S.C. Hui); Mahidol University, Bangkok, Thailand (N. Lindegardh, N.J. White); University of Oxford, Oxford, UK (N. Lindegardh, N.J. White); University of Virginia School of Medicine, Charlottesville, Virginia, USA (F.G. Hayden)

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Table 1

Clinical and laboratory findings in 3 patients with acute encephalopathy associated with influenza infection, Prince of Wales Hospital, Hong Kong*

Clinical and laboratory findings Patient 1 Patient 2 Patient 3
Age, y/sex 76/M 86/F 72/M
Concurrent illnesses Ischemic heart disease Diabetes mellitus, hypertension COPD
Influenza vaccination within 6 mo None None None
Symptoms on examination
Fever >38°C, cough, disorientation, incoherent speech, mental dullness
Fever >38°C, cough, delirious, impaired consciousness, did not follow verbal command
Fever >38°C, cough, disorientation, agitation, incoherent speech, involuntary 4-limb tremor
Focal neurologic sign or meningism Absent Absent Absent
Chest radiograph, consolidation Absent Absent Absent
Antiviral (oseltamvir) None Given Given
Outcome (duration of encephalopathy) Recovered (2–3 d) Recovered (3–4 d) Recovered (6–7 d)
Brain CT scan (noncontrast) Normal Old ischemic changes; known small, calcified meningioma Normal
Virus isolated from NPA
Seasonal (H1N1) 2008
Subtype H3N2
Subtype H3N2
CSF testing results
Opening pressure, cm H2O 11 9 14
Cell count (x 106/L) 1 0
Glucose, mmol/L 4.2 7.4 3.7
Protein, g/L 0.46 0.47 0.16
Virus isolated None None None
RT-PCR for H3 and H1 influenza virus Negative Negative Negative
Bacterial culture Negative Negative Negative
Others HSV, HZV, and enterovirus PCR negative HSV, HZV, and enterovirus PCR negative HSV PCR negative

*COPD, chronic obstructive pulmonary disease; CT, computed tomographic scan; NPA, nasopharyngeal aspirate; CSF, cerebrospinal fluid; RT-PCR, reverse transcription–PCR; HSV, herpes simples virus; HZV, herpes zoster virus. In all cases, there was no hypoglycemia, and liver and renal function test results were normal. C-reactive protein level was elevated in all cases. For patient 3, an electroencephalogram was performed and showed generalized slowing of background consistent with moderate encephalopathic change (similar to that observed in septic encephalopathy) (1,6). Findings are consistent with previous reports on adult cases of influenza-associated encephalopathy: patients are all unvaccinated, pleocytosis and cerebral imaging abnormalities (even with magnetic resonance imaging) are usually absent, and symptoms are generally self-limiting (1,6). Most reports have mentioned influenza A as a cause of encephalopathy, and more commonly subtype H3N2 (16).

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