A complication of severe brain injury is a syndrome of intermittent agitation, diaphoresis, hyperthermia, hypertension, tachycardia, tachypnea, and extensor posturing. To capture the main features of this syndrome, derived through literature review and our own case series, we propose the term paroxysmal autonomic instability with dystonia. We reviewed reports of autonomic dysregulation after brain injury and extracted essential features. From the clinical features, consistent themes emerge regarding signs and symptoms, differential diagnosis, and pharmacological therapies. We used these findings to make recommendations regarding diagnosis and treatment. Paroxysmal autonomic instability with dystonia appears to be a distinctive syndrome after brain injury that can mimic other life-threatening conditions. Early recognition may lead to fewer diagnostic tests and a rational approach to management. Prospective trials of specific drugs are needed to determine optimal efficacy.

We report a study of 73 consecutive children with acute cerebellar ataxia, representing all of the children evaluated at St. Louis Children's Hospital during a 23-year-period to whom this diagnosis could appropriately be assigned. Twenty-six percent had chickenpox, 52% had other illnesses that were presumed to be viral, and in 3% the ataxia was related to immunization. Nineteen percent had no definite prodrome. Sixty children were followed for 4 months or longer after onset of their ataxia (mean, 7.4 +/- 6.0 years). Ninety-one percent (55/60) of these, including all children with chickenpox, recovered completely from ataxia. Eighty-nine percent (39/44) of the children with non-varicella-related ataxia recovered completely from the ataxia, a much better rate of recovery than what was found in prior large studies. One fifth of the children followed for more than 4 months experienced transient behavioral or intellectual difficulties, but only 5 of the 60 children demonstrated sustained learning problems. This study represents the largest reported series of acute cerebellar ataxia and the most complete characterization of the clinical features and outcome of this illness.

The California serogroup viruses are mosquito viruses that cause human infections on five continents. They are maintained and amplified in nature by a wide variety of mosquito vectors and mammalian hosts; they thrive in a remarkably wide variety of microclimates (eg, tropical, coastal temperate marshland, lowland river valleys, alpine valleys and highlands, high boreal deserts, and arctic steppes). In 1993, California serogroup viruses caused 71% of all cases of arboviral illness in the United States, principally La Crosse encephalitis. The 30 to 180 annual cases of La Crosse encephalitis represent 8% to 30% of all cases of encephalitis, rendering this illness the most common and important endemic mosquito-borne illness in the USA. Subclinical or mild infections are much more common. Methods and results acquired from intense study of California serogroup viruses have been applied, with benefit, to the study of the ecology and pathogenesis of many more serious human arboviral illnesses. The evolutionary potential of viruses, with particular reference to the development of more virulent strains, has been studied more closely in the California serogroup viruses than in almost any other agent of human disease.