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Channelopathies Disorders of voltage-gated ion channels are responsible for a diverse group of neurological and muscular diseases. These diseases are now called "channelopathies." Ion channels are normally responsible for the generation of electrical currents across excitable membranes, and the "channelopathies" are characterized by increased or decreased excitability of nerve or muscle. One way of understanding this diverse group of disorders is to subdivide it into toxin-mediated, immune-mediated, and genetically-determined "channelopathies." The largest and most rapidly expanding subgroup is the genetically-determined subgroup secondary to mutations in genes coding for voltage-gated ion channels. The increasing availability of genetic DNA analysis is already allowing a precise diagnosis for many of the genetic "channelopathies." Additionally, understanding the ion channel basis of these diseases should provide the basis for the development of more effective pharmacological treatments. Painful Feet: The Small Fiber
Neuropathies Small fiber neuropathy is a relatively common disorder often associated with systemic conditions, such as diabetes, HIV, and vasculitis. Painful burning feet with diminished pain and temperature perception, and in some cases autonomic dysfunction, characterize this syndrome. Despite the magnitude of the symptoms there are few objective measures to identify and quantify these neuropathies. Skin biopsy and new immunohistochemical staining techniques have facilitated the evaluation of this syndrome. Diagnosis of Peripheral Neuropathies The definition of peripheral neuropathy can range from a condition in which there is damage to nerve fibers within the peripheral nervous system to the more traditional distal symmetric polyneuropathy. Likewise, the causes of peripheral neuropathy are diverse and include metabolic, infectious, paraneoplastic, toxic, drug-induced, nutritional, hereditary, traumatic, immune-mediated or inflammatory, and idiopathic etiologies. Diagnosing the cause of a patient's peripheral neuropathy can therefore be a challenging and complex task, oftentimes with no specific etiology identified. There are, however, useful diagnostic tools and clinical approaches that can simplify this process and successfully lead to a treatable and potentially reversible cause of the neuropathy since, unlike the CNS, the peripheral nervous system can regenerate, leading to a satisfactory outcome for patient and diagnostician alike.
MR Imaging of the Peripheral Nervous System:
MR Neurography MRI imaging of peripheral nerves is useful in combination with clinical evaluation and electrophysiological studies in the diagnosis of a broad range of peripheral nerve disorders, including neoplasia, nerve root compression and entrapment syndromes, trauma, and unexplained plexopathy. MRI can define the specific location of nerve root pathology. MRI can also detect secondary findings of muscle denervation. Rehabilitation of Neuromuscular Disorders While neuromuscular disorders are a diverse group of disorders, most are progressive and will negatively impact function and quality of life. Regardless of the underlying pathophysiology, the principles of assessment of impairment and resultant potential for disability are similar. The general principles of therapeutic exercise, functional retraining, bracing, surgical correction of deformities, use of adaptive aids, and prevention of secondary complications apply to all. Because of the multiple system involvement, unpredictability and variability of progression, a model of care that includes an interdisciplinary approach that is regularly scheduled with standard measures for re-evaluation is best.
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