Neurology, more than any other specialty, rests on clinicoanatomic correlation. Patients do not arrive at the neurologist's office saying "the motor cortex in my right hemisphere is damaged," but they do tell, or show, the neurologist that there is weakness of the face and arm on the left. Since the nervous system is constructed in a modular manner, with different nerves, and different parts of the brain and spinal cord subserving different functions, it is often possible to infer, from a careful physical examination and history together with knowledge of neuroanatomy, which part of the nervous system is affected, even prior to ordering or viewing imaging studies. The neurologic clinician thus attempts, with each patient, to answer two questions: (1) Where is (are) the lesion(s)? and (2) What is (are) the lesion(s)?
Lesions of the central nervous system can be anatomic, with dysfunction resulting from structural damage (examples are provided by stroke, trauma, and brain tumors). Lesions can also be physiologic, reflecting physiologic dysfunction in the absence of demonstrable anatomic abnormalities. An example is provided by transient ischemic attacks, in which reversible loss of function of part of the brain occurs without structural damage to neurons or glial cells, as a result of metabolic changes caused by vascular insufficiency.
A knowledge of peripheral patterns of innervation, and of muscle actions, can also be highly important to the clinician interested in neurological disease. Each spinal ventral root, and each peripheral nerve, innervates a particular set of muscles, and these muscles have very specific actions (Appendix B). Similarly, each spinal dorsal root, and each peripheral nerve, provides sensory innervation to a particular part of the body (Appendix C). By assessing motor and sensory function, it is often possible to localize disease processes impairing spinal root function, or the function of specific nerves, with a high degree of precision.
This chapter gives a brief overview of clinical thinking in neurology and emphasizes the relationship between neuroanatomy and neurology. It has been included to help the reader begin to think as the clinician does and to place neuroanatomy, as outlined in the subsequent chapters, in a patient-oriented framework. Together with the Clinical Illustrations and Cases placed throughout this book and the Appendices, this chapter provides a clinical perspective on neuroanatomy.
SYMPTOMS AND SIGNS OF NEUROLOGIC DISEASES
In taking a history and examining the patient, the neurologic clinician elicits symptoms and signs. Symptoms are subjective experiences resulting from the disorder (ie, "I have a headache"; "The vision in my right eye became blurry a month ago"). Signs are objective abnormalities detected on examination (eg, a hyperactive reflex or abnormal eye movements).
The history may provide crucial information about diagnosis. For example, a patient was admitted to the hospital in a coma. His wife told the admitting physician that "my husband ...