The evidence favors rejection of a causal relation between DT, Td, or tetanus toxoid and encephalopathy (acute or chronic).

Seizures are neurologic events that may occur with or without the loss of consciousness and can include a variety of sensory experiences (e.g., auditory seizures), motor manifestations (e.g., focal motor or tonic-clonic seizures), or both. In addition, seizures can occur with or without fever. Febrile seizures are well-defined, relatively common events that are precipitated by fever in children without a seizure disorder. Afebrile seizures are those that occur in the absence of fever. Recurrent afebrile seizures are referred to as epilepsy and are synonymous with residual seizure disorder. Approximately 0.5 to 2 percent of the population experiences epilepsy. It can occur at any age. Infantile spasms are a type of epileptic disorder in young children characterized by flexor, extensor, and mixed flexor-extensor seizures that tend to occur in clusters or flurries (Kellaway et al., 1979). The earliest manifestations of infantile spasms are subtle and are easily missed, making it difficult to identify the precise age at onset. Incidence rates of infantile spasms range from 0.25 to 0.4 per 1,000 live births. The vast majority of studies report a peak onset between ages 4 and 6 months. Approximately 65 percent of children with infantile spasms go on to have other types of seizures. For a more complete discussion of the definition of seizures, see Chapter 3.

Diphtheria toxin causes a toxic peripheral neuropathy in about 20 percent of cases (Mortimer, 1988), but diphtheria toxin has not been associated with CNS disease. Tetanus is a neurologic disease characterized by severe muscle spasms produced by the potent neurotoxin tetanospasmin (Wassilak and Orenstein, 1988). This neurotoxin can produce three clinical syndromes: (1) localized, (2) generalized (80 percent of cases), and (3) cephalic. In patients with generalized tetanus, the neurotoxin makes its way to the CNS and can then cause spasm of any muscle as well as autonomic nervous system disturbances. Tetanospasms (generalized tonic-tetanic seizure-like activity) can occur, but cognitive functions are not affected. Tetanospasms are generalized muscle spasms, not generalized seizures in which the level of consciousness is affected. Cephalic tetanus is rare and is associated with