Disorders of Consciousness in Systemic Diseases

Alteration of consciousness is the most common neurologic manifestation of systemic disease. Consciousness is composed of two general components: arousal and content. Depending on the anatomic location of brain dysfunction, primary neurologic diseases such as stroke and trauma as well as systemic conditions ranging from organ dysfunction to sepsis may variably affect both arousal and content. Mechanisms of impaired consciousness range from mass effect on brainstem arousal structures to diffuse impairment of bihemispheric cerebral cortical function. Prognosis for recovery is most strongly linked to the underlying cause. This chapter provides an overview of the neuroanatomic structures involved in mediating consciousness, the range of differing mechanisms by which systemic diseases may result in impaired consciousness, and the clinical approach to patient evaluation. Emphasis is placed on the value of the neurologic examination in guiding the need for additional neurologic testing. The diagnosis of brain death is described and the special conditions of vegetative and minimally conscious states are discussed.