NERVOUS SYSTEM ..... POLIOMYELITIS

Nervous System ..... Poliomyelitis

Nervous System: Poliomyelitis

Definition

Poliomyelitis is a viral infection most often recognized by the acute onset of flaccid paralysis. Poliovirus infection occurs in the gastrointestinal tract with spread to the regional lymph nodes and, in a minority of cases, to the central nervous system. Flaccid paralysis occurs in less than 1% of poliovirus infections; aseptic meningitis in another 1%; a minor illness with symptoms including fever, malaise, headache, nausea and vomiting in a further 10%, and the remaining 88% of infections are asymptomatic

Causes

Poliomyelitis is caused by any of the three serotypes of human Poliovirus (genus Enterovirus). Type 1 is isolated from paralytic cases most often and type 3 less so. Circulating wild type 2 poliovirus has not been detected since October 1999. Type 1 most frequently causes epidemics.

Clinical description

Usually the infection is limited to the gastrointestinal tract and nasopharynx, and is often asymptomatic. The central nervous system, primarily the spinal cord, may be affected, leading to rapidly progressive paralysis. Motor neurons are primarily affected. Encephalitis may also occur. The virus replicates in the nervous system, and may cause significant neuronal loss, most notably in the spinal cord. The paralysis of poliomyelitis is usually asymmetric, with fever present at the onset. The maximum extent of paralysis is reached in a short period, usually within 3-4 days. The site of paralysis depends on the location of nerve cell destruction in the spinal cord or brain stem. The legs are affected more often than the arms. Paralysis of the respiration and/or swallowing muscles can be life-threatening. Some improvement in paralysis may occur during convalescence, but paralysis still present after 60 days is likely to be permanent.

Epidemiology

Accurate data on polio case counts are available for 1996 to date from the World Health Organization (WHO) website. As a ...