Neurological complications of swine influenza vaccination.

The emphasis upon the remarkably large number of cases of Guillain-Barre syndrome which resulted from the 1976 National Swine Influenza immunization program in the U.S.A. has obscured the fact that other neurological complications, involving the central nervous system also occurred. The anatomical distribution of lesions is almost identical with that seen following other types of vaccination: involvement of the brain, cerebellum, optic nerve, cranial nerves and spinal cord occurred with approximately the same frequency. 5 instances of the very rare subacute or chronic, progressive, post-vaccinal encephalopathy are described, a situation which is identical to the subacute and chronic forms of polyradiculoneuropathy. In a number of cases, in particular the myelopathies, a subclinical involvement of peripheral nerves was demonstrated by means of electrodiagnostic studies, illustrating the often overlooked fact that central nervous system involvement will mask peripheral nerve lesions. The etiological significance of the swine influenza vaccination was overlooked and completely erroneous diagnoses were established in a surprisingly large number of the 26 new cases reported here.