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Limb pain, diminished sensation (numbness), altered sensory perception (paresthesias and dysesthesias) and impaired function due to weakness are exceedingly common complaints in the practice of medicine. Many individuals with one or more of these symptoms, particularly pain in isolation, have musculoskeletal problems. Some of these individuals may have sensory symptoms as well. Although this suggests nerve involvement, it is not uncommon to be unable to find objective evidence of nerve pathology particularly if the sensory symptoms are intermittent and vague in their anatomic distribution. By the same token, many of these patients have the perception of weakness that may result from limitations imposed by pain. Not uncommonly, however, patients with complaints of limb pain, sensory symptoms, and altered function will have focal nerve injuries affecting the nerve roots, lumbosacral plexus, or individual peripheral nerves, the subject matter of this chapter.
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The purpose of this chapter is to provide a conceptual framework by which to evaluate and manage patients with focal lower limb complaints. The specific goals are to provide strategies to accurately diagnose and then manage focal nerve injuries. This begins by distinguishing them from the musculoskeletal causes of monomelic symptoms described in Chapter 36. Subsequently, as with all neurologic problem-solving exercises, localization is attempted to nerve roots, plexus or one or more individual nerves. As etiologies of nerve injury vary with anatomic locus, the benefit of localization is to limit differential diagnostic considerations, facilitate etiologic diagnosis and provide optimal management. Consideration of chronologic course and risk factors will aid in differential diagnosis.
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The format of this chapter will parallel that of the preceding chapter on analogous disorders of the upper extremities to which the reader is referred regarding relevant anatomy, pathophysiology, and electrodiagnostic (EDX) evaluation. To avoid redundancy, these subjects will only be addressed when there are relevant differences between the upper and lower extremities. A detailed review of the clinical features, etiologies, evaluation, and management of individual focal neuropathies of the lower extremities will be provided. As in other chapters in this book, descriptions will rest on a foundation of published data but will be expanded upon by the personal experiences of the authors.
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LUMBOSACRAL NERVE ROOTS
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There are a few, clinically relevant differences in anatomy and nomenclature between the upper and lower limbs that require repetition. The organization of nerve roots is in many ways identical to that in cervical spine. One notable exception is that dorsal root ganglia may reside in an intraspinal location within the lumbosacral spine. In some cases, this results in mechanical nerve root compression distal rather than proximal to the dorsal root ganglion, producing a potentially confusing pattern of EDX findings to those unfamiliar with this anatomical variant.1
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In the lumbosacral cord the nerve roots have a more oblique, descending trajectory than their cervical counterparts, due to the ...