Once a peripheral disorder has been established, it is necessary to determine which part of the peripheral nervous system is involved. A localized process, such as numbness and tingling of the fifth and half of the fourth digits of one hand, strongly suggests a focal lesion (ulnar nerve). The lesion may involve the nervous system at a number of locations: the nerve, plexus, or root. Basic knowledge or the aid of an anatomy text or neurology handbook should be sufficient to accurately localize focal lesions of these types. Figure22.5-1 shows a schematized view of the peripheral nervous system and illustrates the signs associated with disease of specific parts of the neuromuscular system. Most muscle-related processes result in weakness of large proximal muscles, and patients may have a difficult time lifting their arms over their heads or arising from a seated position. Pain and tenderness of the muscles occur commonly (although usually these are not predominant symptoms and if not accompanied by weakness rarely indicate myopathy), and creatine phosphokinase (CPK) is usually elevated, sometimes dramatically. Diseases that affect other components of the peripheral nervous system seldom cause muscle tenderness and elevations in CPK. Neuromuscular junction processes also affect large proximal muscles and frequently affect the bulbar musculature, resulting in pupillary dysfunction, diplopia, dysarthria, or dysphagia. Unlike muscle and neuromuscular junction disorders, neuropathies frequently affect both the motor and sensory systems; because these diseases most severely affect longer nerves, distal power is reduced most dramatically. Polyradiculopathy, which frequently follows a progressive and stepwise course, usually results in electrical pain sensations, assorted sensory abnormalities, areflexia, and weakness.
FIG. 225-1. Schematic view of the neuromuscular system and typical findings with disease of each component of the system. Abbreviations: DRG, dorsal root ganglion; NMJ, neuromuscular junction.
Once localization of the peripheral problem is accomplished, efforts should be made to pinpoint the etiology. Specific historical points that always should be addressed include the time course of the illness, whether there are diurnal fluctuations in the symptoms, other systemic symptoms or conditions, a review of medications, and antecedent illnesses. A serum chemistry and metabolic profile and creatine kinase are frequently useful blood tests in the emergency department (ED) setting. Further testing is usually deferred in the acute setting but may include a variety of blood tests, nerve conduction studies, electromyography, lumbar puncture, and nerve/muscle biopsy.
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