A large number of viruses are able to affect the nervous system. Among the enteroviruses alone, nearly 70 distinct serologic types are associated with CNS disease, and additional types from this family of viruses and others are still being discovered. Rather than considering them individually, there are only a limited number of ways in which they express themselves clinically: (1) acute aseptic (“lymphocytic”) meningitis; (2) a less-common recurrent meningitis; (3) acute encephalitis and meningoencephalitis; (4) ganglionitis (herpes zoster); (5) chronic invasion of nervous tissue by retroviruses, that is, HIV and tropical spastic paraparesis (HTLV-I); (6) acute anterior poliomyelitis; (7) reactivation of chronic viral infections including the viruses causing PML and subacute sclerosing panencephalitis (SSPE).
The term aseptic meningitis was first introduced to designate what was thought to be a specific disease—“aseptic” because bacterial cultures were negative. The term is now applied to a symptom complex that is produced by any one of a number of infective agents, the majority of which are viral but a few of which are bacterial (mycoplasma, Q fever, other rickettsial infections) and some of which are immune or a reaction to a chemical irritant. Because aseptic meningitis is rarely fatal, the precise pathologic changes are uncertain but are presumably limited to the meninges. Conceivably, there may be some minor changes in the underlying brain itself, but these are of insufficient severity to cause neurologic symptoms and signs or to show changes on imaging studies.
In outline, the clinical syndrome of aseptic meningitis consists of fever, headache, signs of meningeal irritation, and a predominantly lymphocytic pleocytosis in the spinal fluid with normal glucose. Usually the onset is acute and the temperature is elevated, from 38 to 40°C (100.4 to 104°F). Headache that is more severe than that associated with other febrile states is the most frequent symptom. A variable but usually mild degree of lethargy, irritability, and drowsiness may occur. Photophobia and pain on movement of the eyes are common additional complaints. Stiffness of the neck and spine on forward bending attests to the presence of meningeal irritation (meningismus), but at first it may be so slight as to pass unnoticed. When there are accompanying neurologic signs, they too tend to be mild or fleeting: paresthesia in an extremity, or wavering Babinski signs.
Systemic symptoms and signs aside from fever are infrequent and depend mainly on the more mundane effects of the invading virus; these include sore throat, nausea and vomiting, vague weakness, pain in the back and neck, conjunctivitis, cough, diarrhea, vomiting, rash, petechia, hepatitis, adenopathy, or splenomegaly. The childhood exanthems associated with meningitis and encephalitis (varicella, rubella, mumps) produce well-known eruptions and other characteristic signs. An erythematous papulomacular, nonpruritic rash, confined to the head and neck or generalized, may also be a prominent feature, particularly in children, of certain echoviruses and Coxsackie viruses. Adults may also demonstrate a nonspecific rash but this finding is not specific. An enanthem (herpangina), taking the form of a vesiculoulcerative eruption of the buccal mucosa, may also occur with these viral infections.