The evaluation of patients with suspected neurologic disease remains first and foremost a bedside exercise. Accurate diagnosis requires consideration of individual patient and disease differences. Despite the benefits of evidence-based medicine, conclusions are more relevant to populations than to individuals. Confounding variables that are part of the human experience may be overlooked or overemphasized by testing algorithms. This textbook will repeatedly emphasize the strongly held philosophy of its authors, that is, patient management flows from an accurate diagnosis. An accurate diagnosis is most likely to be obtained based on a differential diagnosis driven by clinical assessment and hypotheses. These hypotheses should be formulated on the basis of the principles of neurologic localization, the correlation of the chronologic course of symptom development with the behaviors of differing disease conditions, and the application of risk factor analysis. Ideally, the tests described in the subsequent two chapters and throughout the text would be utilized with the primary intent of resolving a clinically established differential diagnosis ideally to prove a working diagnosis. As all tests are potentially fallible, the credibility of their results diminishes when they are used as screening procedures. A laboratory abnormality, occurring without the context of clinical correlation, fails to establish the desired confidence in a cause and effect relationship with the patient's complaint(s). Metaphorically, laboratory tests are analogous to a carpenter's tools. They are of great value when placed in the hands of a skillful artisan, but are potentially damaging if used injudiciously.
In this book, a neuromuscular disorder will refer to any condition that affects the structure and/or function of any component of the neuromuscular system, beginning and working centrifugally from the cell bodies of the anterior horn and dorsal root ganglion. This will include disorders of nerve root, plexus, nerve, neuromuscular junction and muscle. In essence, with the exception of disorders affecting small, poorly, or unmyelinated nerve fibers such as the small fiber or pure autonomic neuropathies, a neuromuscular disorder may alternatively be defined as one that can be potentially detected by electromyography and nerve conduction studies. Disorders affecting the peripheral autonomic system or cranial nerves will be discussed only as necessary to better understand diseases affecting their somatic and spinal counterparts.
Many neuromuscular disorders are the result of or are influenced by single gene or complex genetic mutations. Many of these patients will not recognize the hereditary nature of their disease. This may be due to a recessive inheritance pattern, spontaneous mutation, false paternity, or incomplete or delayed penetrance. Frequently, it is due to a lack of familiarity with the medical issues of other family members. In suspected hereditary disease, acquisition of family history, particularly if done in a cursory fashion, may be insufficient. Examination of other family members, even if only briefly, is strongly recommended when heritable diseases are considered.
The differential diagnosis of disorders of the neuromuscular system is in part age-dependent. The differential diagnosis of neuromuscular ...