Evidence for persistent enterovirus infection of the central nervous system in patients with previous paralytic poliomyelitis.

It has been suggested that late onset neurological deterioration after poliomyelitis may be due in some cases to persistent poliovirus infection of the central nervous system. In view of this, we decide to determine whether polioviruses and other enteroviruses can persist in the central nervous system. In a previous study, one of us (M.K.S.) reported serological evidence of persistent poliovirus infection of the central nervous system (CNS) in a proportion of these patients. We have now studied cerebrospinal fluid (CSF) from these patients for the presence of enterovirus RNA sequences using the polymerase chain reaction (PCR). Enteroviral RNA was detected in 3 of 24 patients with a clinical diagnosis of post-polio syndrome, but in none of 36 patients with stable poliomyelitis, and none of 36 patients with other neurological conditions of noninfective origin. All 3 patients in whom viral RNA was detected had high intrathecal levels of poliovirus-specific oligoclonal IgM bands. In a second study we examined formalin-fixed postmortem CNS tissue from 7 patients with a history of paralytic poliomyelitis. Enterovirus RNA was detected in tissue from the spinal cord from 3 patients, but not in the cerebral cortex. We are now conducting a larger prospective, blind study of patients with evidence of late deterioration. Analysis of the first 30 patients studied revealed the presence of enterovirus RNA in CSF of 1 of 4 patients with unexplained late-onset post-polio weakness, 1 of 6 with some evidence of clinical deterioration, but none of 20 without inexplicable signs of post-polio weakness. Enteroviral RNA was also detected in spinal cord from 2 of 3 patients who died from other causes during this study. These studies provide virological evidence that enteroviruses may persist in the CNS of man. Further study is required in order to understand fully the biological and clinical significance of these findings.