Idiopathic bilateral carpal tunnel syndrome in a 9-month-old infant presenting as a pseudo-dystonia.

BACKGROUND: Carpal tunnel syndrome is the most common focal peripheral neuropathy seen in most electrophysiological laboratories. Although the incidence of carpal tunnel syndrome in adults is 50 to 150 cases per 100,000 people, it is rare in children. There are less than 200 case reports of carpal tunnel syndrome in children, with mucopolysaccharides and mucolipidosis being the most frequent cause. Idiopathic carpal tunnel syndrome with childhood onset occurs in less than 0.2% of cases. PATIENT: We describe a 9-month-old infant who presented with intermittent abnormal posturing movement of both hands. RESULTS: The clinical presentation and the electrophysiological studies confirmed the diagnosis of carpal tunnel syndrome. His dystonic posturing had disappeared completely 3 weeks after surgical release of both flexor retinaculi. CONCLUSION: We are not only reporting the youngest child with carpal tunnel syndrome, but we also report a new cause of abnormal movement disorder in children.

Frequency-dependent conduction block in ulnar neuropathy localized to the elbow.

OBJECTIVE: To determine whether frequency-dependent conduction block (FDB) occurs in acute ulnar neuropathies localized to the elbow. METHODS: High-frequency nerve stimulation (30Hz, 20 stimuli) was applied to the ulnar motor nerve above and below the elbow in controls (15) and in patients with short duration (between 2 and 16 weeks) ulnar neuropathy localized to the elbow (10) with evidence of moderate to severe conduction block and slowing. RESULTS: FDB was not observed in any of the 10 subjects tested. Three of these subjects were seen in follow-up; studies in two of these subjects, during the recovery period, did however demonstrate FDB with a similar pattern to that observed previously in CTS. CONCLUSIONS: This study has demonstrated that the remaining unblocked ulnar motor fibers across the elbow in acute ulnar neuropathy with conduction block, do not demonstrate FDB in response to stimulation at 30Hz. SIGNIFICANCE: These results suggest that FDB may not occur in the unblocked fibers in ulnar neuropathy despite evidence of conduction slowing. These results differ from previous observations in CTS and imply that demyelinating lesions (conduction block versus slowing) respond differently to high-frequency stimulation.

Effect of maximal voluntary contraction on the amplitude of the compound muscle action potential: implications for the interpolated twitch technique.

The compound muscle action potential (M(MAX)) during a maximal voluntary contraction (MVC) may be measured to determine if the motor nerve has been supramaximally stimulated during the interpolated twitch technique (ITT). Ten males performed isometric knee extension MVCs. M(MAX) for the vastus medialis was recorded during MVC and rest. To examine the effect of stimulating electrode movement, the M(MAX) of the thenar group and antidromic sensory nerve action potentials (SNAPs) to the third digit were recorded in a separate experiment. M(MAX) during MVC was reduced by 18% (P < 0.0001) and 43% (p < 0.0001) for the quadriceps and thenar group, respectively. The SNAP amplitude was not different between rest and MVC (P = 0.18). Reduction of M(MAX) during MVC suggests that some motor axons are refractory and unable to respond to a superimposed maximal stimulus. These results have implications for the sensitivity of the interpolated twitch technique.

Localization of frequency-dependent conduction block in carpal tunnel syndrome.

Frequency-dependent conduction block (FDB) has been demonstrated in subjects with carpal tunnel syndrome (CTS) when the median nerve was stimulated at 30-Hz frequency proximal to the carpal tunnel (CT). However, it was still questionable whether FDB occurred within the region of the CT or more distally. High-frequency nerve stimulation (HFNS) was performed in controls and in CTS subjects while stimulating the median nerve proximal and distal to the carpal tunnel. The degree of FDB was measured by comparing the 20th thenar CMAP with the 1st following a train of 20 stimuli at 30-Hz. FDB occurred across the CT in 11/12 studies (91.7%) and across the distal portion of the palmar aponeurosis-distal terminal motor branches in 5 of the 11 studies (41.7%). These results suggest that the safety margin for impulse transmission can be impaired distal to the presumed site of injury in CTS.

Muscle strength and fatigue in patients with generalized myasthenia gravis.

Myasthenia gravis (MG) is characterized by fatigue and fluctuating muscle weakness resulting from impaired neuromuscular transmission (NMT). The objective of this study was to quantify, by direct measurement of muscle force, the strength and fatigue of patients with MG. A maximal voluntary isometric contraction protocol of shoulder abductors was used in conjunction with conventional fatigue and disease-severity instruments. Results from patients with (D-MG) and without (ND-MG) decrement on repetitive nerve stimulation (RNS) of the spinal accessory and axillary nerves were compared with healthy controls. Patients with MG reported greater fatigue than controls. Muscle strength was lowest in the D-MG group, followed by the ND-MG group and controls. Normalized shoulder abduction fatigue and recovery values did not differ between the D-MG and ND-MG groups or controls. The RNS decrement appears to relate best to disease severity and muscle weakness but not to objective measures of fatigue in this population.

Determination of the best electrode position for recording of the diaphragm compound muscle action potential.

To determine the optimal recording site for phrenic nerve conduction studies, six different recording techniques were compared in 11 healthy volunteers (22 phrenic nerves). The mean diaphragm compound muscle action potential (CMAP) amplitude, side-to-side difference, and the number of studies with a false-positive result (CMAP amplitude <0.30 mV) were compared for each technique. The largest amplitude (0.65 +/- 0.23 mV, range 0.30-1.2 mV) with good right-left agreement (mean difference 0.15 mV) and no false positives was obtained using technique 1, where the G1 electrode was positioned 5 cm above the xiphoid process and G2 16 cm from G1 along the costal margin. This was also the easiest technique to perform. It does not require rib counting, which may be difficult and inaccurate, especially in overweight patients. At least one false positive occurred with each of the remaining five techniques.

Frequency-dependent conduction block in carpal tunnel syndrome.

Frequency-dependent conduction block (FDB) across segments of demyelination in response to high-frequency nerve stimulation has been well demonstrated in animals and has been explored in humans. However, attempts to demonstrate this phenomenon in sensory fibers involved in entrapment neuropathies have been unsuccessful. Therefore, we investigated the effects of high-frequency nerve stimulation in the median motor nerve in patients with carpal tunnel syndrome (CTS) with moderate to severely increased distal motor terminal latencies (MTL). As a group, the mean decrease in negative peak amplitude (npAmp) during 20 stimuli at 30-HZ frequency was significantly greater in CTS subjects (-11.3%) than in controls (+7.9%). The degree of FDB was greater when MTL was more prolonged (i.e., -4.9% at 5.0 ms and -25.3% at 9.4 ms) and FDB was more pronounced at higher stimulation frequencies (20 and 30 HZ). Our results suggest that the safety margin for impulse transmission is impaired in the motor axons of patients with a focal demyelinating lesion. These findings may correlate with the observation of weakness in the absence of conduction block in patients with entrapment neuropathies.

Transient forearm conduction block in the median nerve.

We present two cases referred for electrophysiological confirmation of carpal tunnel syndrome (CTS). Initial nerve conduction studies were normal. Approximately 20 min into the examination, both patients developed sensory symptoms and weakness in the distal median nerve territory while the elbow was extended and forearm supinated. Further studies demonstrated complete conduction block across the forearm in the median motor and sensory nerve fibers. When measurable, conduction velocities remained normal or were modestly slow. Complete clinical and electrophysiological recovery occurred within 2 min following forearm pronation, suggesting that dysfunction was probably due to focal transient ischemia. Patients describing increased sensory symptoms during routine electrophysiological assessments for CTS should be investigated to rule out the possibility of a more proximal abnormality.