[Show abstract][Hide abstract] ABSTRACT: With the introduction of highly active antiretroviral therapy peripheral neuropathies have become the most common neurological complications in HIV infection. The frequency and spectrum of these neuropathies are changing, as the various toxic and immune factors are modified by new treatment strategies. Recent studies have provided a better understanding of the risk factors, markers and relevant pathogenic mechanisms, and a thorough review of these is critical for an improved understanding of this important and increasingly common complication.
The combined use of dideoxynucleosides, in association with immune-mediated mechanisms triggered by HIV infection, are critical in the development of distal sensory polyneuropathy. Valuable markers of neuropathy such as intraepidermal nerve fiber density from skin biopsies have been validated and promise to be a valuable tool in the detection and monitoring of distal sensory polyneuropathy. Markers of virological activity have also been associated with the severity of neuropathic pain in distal sensory polyneuropathy. In some instances, the enhanced viral suppression from antiretroviral agents may actually improve or decrease the frequency of certain types of neuropathy. New evidence supports mitochondrial toxicity as a principal mechanism for dideoxynucleoside-associated sensory neuropathy, and questions arise about enhanced risk with pre-existing mitochondrial defects. Confirmed treatments are limited to the reduction of symptoms, with a need for the further investigation of corrective therapies.
Increased and improved surveillance for HIV-associated neuropathy will allow earlier interventions to improve quality of life and prevent severe toxicities. A better understanding of the prevailing mechanisms will allow for more effective interventions.
Current Opinion in Neurology 07/2003; 16(3):403-9. · 5.73 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Fabry's disease is commonly associated with a painful, debilitating neuropathy. Characterization of the physiological abnormalities is an important step in evaluating response to specific therapies. Twenty-two patients with Fabry's disease, and with relatively preserved renal function, underwent conventional and near-nerve conduction studies, electromyography, sympathetic skin responses, and quantitative sensory testing (QST). Nerve conduction studies were mostly normal except for an increased frequency of median nerve entrapment at the wrist in 6 (27%) patients. Sympathetic skin responses were preserved in 19 of 20 (95%) of the patients. The QST showed increased or immeasurable cold and warm detection thresholds in patients, significantly different from controls (n = 28) in the hand (P < 0.001, P = 0.04, respectively) and foot (P < 0.001 for both). Cold thresholds were more often abnormal than were warm thresholds. Vibration thresholds were normal in the feet and, in some patients, elevated in the hand only, probably due to frequent median nerve entrapment at the wrist. Our findings suggest that the neuropathy of Fabry's disease is characterized by an increased prevalence of median nerve entrapment at the wrist and by thermal afferent fiber dysfunction in a length-dependent fashion, with greater impairment of cold than warm sensation.
[Show abstract][Hide abstract] ABSTRACT: We assessed the cutaneous silent period (CSP) in 24 patients with Fabry disease with small-fiber sensory neuropathy and 12 normal subjects to test the hypothesis that small-diameter afferents are responsible for producing the CSP. Sensory nerve conduction studies and quantitative sensory testing for cold and vibration detection thresholds were also measured. Overall, Fabry patients had impaired thermal, but not vibration, detection thresholds, with greatest impairment in the feet. In the upper extremity, CSP latencies, duration, and suppression of electromyographic activity (EMG) did not differ. In the lower extremity, patients had reduced suppression of EMG during the CSP compared to normal controls. CSP durations exhibited a bimodal distribution in patients, including a subset of seven patients with durations shorter than all controls. This subset had profound loss of thermal sensation in the feet, but this was also true of some patients who had normal CSPs. Patients with shortened CSPs had modestly elevated vibration thresholds and reduced sensory potentials in comparison to patients with normal CSPs. Reduced CSPs in Fabry patients are associated with, but not entirely explained by, the severity of small-fiber neuropathy as measured by quantitative sensory testing. The possibility that large-diameter fibers provide a minor contribution to producing the CSP should be considered.
[Show abstract][Hide abstract] ABSTRACT: Polyclonal immunoglobulin M antibodies to the monosialoganglioside GM2, sulfoglucuronyl glycolipids, and sulfatide were detected by thin-layer chromatography and enzyme-linked immunosorbent assay in the serum of a patient with melanoma and chronic inflammatory demyelinating polyneuropathy. Both the patient's serum and polyclonal antibodies against GM2 reacted strongly with a biopsy of melanomatous tissue from the patient, suggesting a process of molecular mimicry.
[Show abstract][Hide abstract] ABSTRACT: Central motor conduction time, a useful measure for studying central motor pathways, is calculated by determining the difference between the latency of motor-evoked potentials and peripheral conduction time. The intraindividual trial-to-trial variability of central motor conduction time and the discomfort associated with three methods of measuring peripheral motor conduction time (F-wave latency, cervical magnetic stimulation, and cervical needle stimulation) were studied in 5 healthy subjects with the use of transcranial magnetic stimulation to elicit motor-evoked potentials. Central motor conduction time was calculated by using measurements, made on 3 separate days, from the same three muscles on each hand. A visual analog pain scale was used to determine the level of discomfort for each method. Intraindividual trial-to-trial variability of central motor conduction time was similar for all methods, with coefficients of variation of 13% for the F-wave latency, 15% for cervical magnetic stimulation, and 11% for cervical needle stimulation. The last method was significantly more painful than the other two methods; there was no significant difference in discomfort between the F-wave method and cervical magnetic stimulation. To assess peripheral motor conduction time, when determining central motor conduction time, either the F-wave method or cervical magnetic stimulation is preferable to cervical needle stimulation.
[Show abstract][Hide abstract] ABSTRACT: Peripheral neuropathy is infrequently reported in children with HIV infection, but may be underrecognized. To provide a better understanding of the patterns of peripheral neuropathy in these children, we surveyed the charts of 50 children with HIV infection referred to the EMG laboratory at the National Institutes of Health for evaluation of suspected peripheral neuropathy. Twelve children had an abnormal nerve conduction study. The findings suggested a distal sensory or sensorimotor axonal neuropathy in seven children, median nerve compression at the carpal tunnel in three, a demyelinating neuropathy in one child, and a lumbosacral polyradiculopathy in one adolescent. Distal symmetric polyneuropathy occurred mostly in older-aged children.
[Show abstract][Hide abstract] ABSTRACT: Because electrophysiologic, clinical, and histopathologic observations have suggested that inclusion body myositis (IBM) may have a coexistent neurogenic component, we used macro-electromyography (macro-EMG) to search for changes in the motor unit territory and signs of reinnervation. We studied 11 patients, aged 53 to 77 years (mean, 65.2 years), with typical, nonfamilial IBM lasting a mean of 8.5 years, and eight healthy volunteers aged 54 to 70 years (mean, 64.6 years), as control subjects. Nerve conduction studies showed focal abnormalities in 5 of the patients, but no evidence of a polyneuropathy. Concentric needle EMG in various proximal and distal muscles of the upper and lower limbs revealed short- or long-duration complex motor unit potentials (MUPs) or a mixture of both types of MUPs. Macro-EMG studies in the tibialis anterior muscle showed smaller macro-MUP amplitudes and areas in patients than in normal subjects. Four patients had abnormal macro-EMG studies with an increased number of small macro-MUPs, 1 patient had an equivocal study with large-amplitude but normal-area macro-MUPs, and the remaining 6 patients had normal studies. These findings are consistent with a primary muscle disorder similar to those seen in other myopathies. We conclude that macro-EMG does not support a coexistent neurogenic component in patients with IBM compared with normal subjects of similar age.
[Show abstract][Hide abstract] ABSTRACT: Macro-electromyography (macro-EMG) studies have provided important information about the size of the motor units and the degree of reinnvervation in clinically affected muscles of patients with a history of poliomyelitis and postpolio syndrome. The study of clinically unaffected muscles and correlation of their electrophysiologic characteristics with the muscle architecture could provide meaningful information about the ongoing subclinical denervation. We performed macro-EMG and concomitantly measured fiber density in the clinically unaffected gastrocnemius muscle of 10 patients with postpolio syndrome and 10 normal subjects of similar age. We also performed biopsies on the gastrocnemius muscle of 8 of the patients. The median amplitude and area of the macro-motor unit potentials (macro-MUPs) were increased in 8 of the 10 patients, and occasionally were five times as large as the mean median value for the normal subjects. Seven biopsy specimens showed moderate to very large fiber-type grouping. In 5 patients, there was correlation between the electrophysiologic and histologic indices of reinnervation. Amplitude and area of the macro-MUPs were associated with the muscle fiber cross-sectional area. We conclude that clinically unaffected muscles of patients with postpolio syndrome often have large motor units as the result of effective reinnervation after the original motor neuron loss. In spite of possible differences in the cytoarchitecture of muscles affected to different degrees, macro-EMG and fiber density measurements are reliable noninvasive techniques for studying the extent and effectiveness of reinnervation in patients with postpolio syndrome.
[Show abstract][Hide abstract] ABSTRACT: Uncertainty about motor and sensory contributions in abnormal nerves has limited the use of mixed nerve action potentials (MNAPs). We recorded MNAPs in 21 patients with an acquired demyelinating neuropathy, 18 age-matched control subjects, and 10 patients with an axonal polyneuropathy. Bipolar and unipolar recordings from median and ulnar nerves were made above the elbow after electrical stimulation of the nerves at the wrist. Antidromic digital sensory action potentials and motor conduction velocity were also recorded for both nerves. In 19 median and 12 ulnar nerves from demyelinating polyneuropathy patients, compared with control subjects, MNAP amplitudes were significantly reduced (mean, 6 microV vs. 31 microV), MNAP velocities were mildly reduced (mean, 50 m/s vs. 62 m/s), motor conduction velocities were significantly reduced (mean, 33 m/s vs. 57 m/s), and MNAPs were significantly dispersed, with markedly prolonged rise times (mean 2.0 ms vs. 1.0 ms). Compared with the axonal polyneuropathy group, MNAP amplitudes from the median nerve were similarly reduced (mean, 8 microV vs. 9 microV), MNAP velocities were only slightly slower (mean, 52 m/s vs. 58 m/s), but the rise times were significantly prolonged (mean, 2.0 ms vs 1.2 ms). We conclude that, in acquired demyelinating neuropathies, the onset and, in some cases, the whole MNAP is from afferent fibers, which can be abnormally dispersed, and that, over the same segment MNAP velocity is less affected than motor conduction velocity.