Background: Early or R1 motor response from the orbicularis oculi (o. oculi) muscle is obtained only unilaterally from ipsilateral supraorbital nerve stimulation, while the late or R2 response is present bilaterally during ipsilateral and contralateral stimulation. Case material: A 29-year-old woman developed horizontal diplopia, left facial numbness, and occasional left eyelid twitching. Otherwise, she was healthy. Examination showed left 6th cranial nerve palsy and decreased left facial sensation. There was no blepharospasm, myokymia, or facial weakness. Electrophysiologic findings: Peripheral motor nerve conduction study of both facial nerves and needle EMG of left facial muscles showed no abnormality. Blink reflex study revealed no R1 response from the left o. oculi muscle on ipsilateral supraorbital nerve stimulation, but present during contralateral stimulation (latency = 11.4 ms). R2 responses from the left o. oculi muscle showed normal latencies during contralateral (31.2 ms) and ipsilateral stimulation (30.8 ms) stimulation. R1 latency from the right o. oculi muscle was 10.0 ms, and the R2 responses showed normal latencies during contralateral (31.0 ms) and ipsilateral (31.9 ms) stimulation. Conclusions: Absent R1 response during ipsilateral stimulation suggests abnormalities in the main sensory nucleus of the pons. Presence of an R1 response from the o. oculi muscle during contralateral supraorbital nerve stimulation is unusual. This may indicate cross excitation of the facial nucleus from contralateral trigeminal sensory nerve impulses that are not involved in the usual multi-synaptic pathways responsible for eliciting the R2 contralateral response. Perhaps this is a result of focal CNS demyelination.

Thenar muscles are primarily innervated by the median nerve. However, compound muscle action potentials (CMAPs) evoked by ulnar nerve stimulation can be recorded at the thenar region due to proximity of some ulnar-innervated muscles, and from volume conduction events. This study was to determine if loss of thenar muscle mass from carpal tunnel syndrome (CTS) could alter the size of ulnar CMAPs obtained at the thenar region, because of changes in the physical surroundings and electrical conductivity. Supramaximal CMAPs were recorded over the thenar eminence to electrical stimulation of the ulnar nerve at the wrist and median nerve at the palm in 102 hands with CTS. Needle EMG was done in the thenar muscles. Severity of needle EMG abnormality was negatively correlated with median-evoked CMAP amplitude (r = -0.76), but not with ulnar-evoked CMAP amplitude (r = -0.12). There was no correlation between the absolute amplitudes of the median and ulnar CMAPs (r = -0.13). Needle EMG abnormality had modest negative correlation (r = -0.43) with median/ulnar CMAP amplitude ratio. Mean median/ulnar CMAP amplitude ratios for normal EMG and for mild, moderate, and severe needle EMG abnormalities were 3.72, 3.31, 1.56, and 0.37, respectively. The absolute amplitude of the ulnar CMAP recorded at the thenar area does not seem to be influenced significantly by the degree of thenar muscle loss (atrophy) from median nerve pathology. However, if the median/ulnar CMAP amplitude ratio falls below 0.5, the study suggests severe loss of motor units in the thenar muscles.

This study was to determine if the size of the compound muscle action potential (CMAP) recorded from a large muscle, such as the biceps brachii, can be correlated with the muscle mass or volume that is generating the electrical response. Supramaximal CMAPs were obtained from 32 normal biceps brachii muscles to electrical stimulation of the musculocutaneous nerve at the axilla. Upper-arm circumference was measured with biceps muscle relaxed (elbow extended) and during muscle contraction (elbow flexed). For all muscles, mean CMAP duration was 16.45 ms, amplitude was 10.50 mV, and area was 96.13 mVms. Body mass index and absolute upper-arm circumference (biceps muscle relaxed or contracted) did not correlate with CMAP duration, amplitude, and area; Pearson correlation coefficients (r) ranged from -0.24 to 0.16. However, the difference (increment) in upper-arm circumference due to biceps muscle contraction correlated with CMAP duration (r = 0.47), amplitude (r = 0.67), and area (r = 0. 75). CMAP size (amplitude and area) correlated well with biceps brachii muscle volume as estimated by the increase from baseline in upper-arm circumference during muscle contraction. The difference (increment) in upper-arm circumference due to biceps muscle contraction reflects mainly the underlying biceps muscle bulk, and eliminates other variables such as thickness of the subcutaneous tissues and triceps brachii muscle.

Clinical and electrophysiologic findings on 136 patients (39 women and 97 men; mean age = 33.2 years) with traumatic peripheral nerve injuries were reviewed. Motor vehicular collisions (MVCs) caused 39.7% and gunshot wounds (GSWs) produced 32.4% of the nerve injuries studied. Other factors such as falls, lacerations, work-related injuries, knife wounds, and blunt traumas produced the remaining 27.9% of the nerve injuries in the study group. Peripheral nerves of the upper limbs (79.6%) were disproportionately damaged in MVCs compared with those of the lower limbs (20.4 %). In MVCs, the brachial plexus was involved in 37.0% and radial nerve in 22.2% of the cases. Patients with GSWs were predominantly men (88.6%) and slightly younger (mean age = 28.7 years). The frequencies of peripheral nerve injuries to the upper extremities (52.3%) and lower extremities (45.5%) were nearly similar in GSWs. The sciatic nerve was involved in 34.1% of GSWs, followed by the ulnar nerve (22.7%).

It has been observed anecdotally that diabetics are usually non-ketotic at the time of their seizure presentation. In order to establish some validity on this observation, we reviewed the medical records of patients with diagnoses of diabetes and seizure. Study subjects were diabetics presenting with seizures. Control subjects were random sampling of all diabetics. In 51 diabetics presenting with seizures, 38 were nonketotic and 13 were ketotic. In the control group of 119 diabetics, 63 were non-ketotic and 56 were ketotic. There were no significant differences in the serum levels of glucose, sodium, potassium, chloride, and calcium between the seizure and control groups. Multiple regression analysis showed that non-ketotic patients were at risk for developing seizures with an odds ratio of 4.03 (p=0.001). Male sex and type 1 diabetes were also risk factors while age was not a risk factor. Keto-acidosis may play a role in preventing epileptic seizures from occurring in diabetic patients.

Distal entrapment of the ulnar nerve at the wrist and hand (Guyon's syndrome) is a relatively uncommon condition. It may present with a confusing permutation of sensory and motor symptoms, depending on which branches of the ulnar nerve are involved Electrodiagnostic test procedures are often helpful in sorting out this quandary. Electrophysiologic studies that include electrical stimulation of the nerve at the palm, in addition to stimulation of the ulnar nerve at other locations, are useful in demonstrating the focal nerve conduction abnormality that is involved in the entrapment. Sensory and motor recordings from palmar stimulation of the ulnar nerve are not technically difficult procedures, and can be performed routinely.

Nerve conduction study was performed on 71 diabetic patients with distal sensorimotor axonopathy. Of 76 lower limbs studied, 46.1% showed no recordable sural compound sensory nerve action potential (CSNAP), and 55.3% no superficial peroneal CSNAP. Only 2.6% revealed no recordable compound muscle action potential (CMAP) from the abductor hallucis (AH) muscle, and 9.2% showed no obtainable CMAP from the extensor digitorum brevis (EDB) muscle. There were fairly good positive correlations between the amplitudes of the sural CSNAPs and AH CMAPs (r = 0.66), and between the superficial peroneal CSNAP and EDB CMAP amplitudes (r = 0.63). There were no instances in which a CSNAP could be obtained from the sural or superficial peroneal sensory nerve, but a CMAP could not be recorded from the AH or EDB muscle. If the CMAP amplitudes of the AH and EDB muscles were reduced to less than 0.3 mV, usually a CSNAP could longer be recorded from the sural and superficial peroneal sensory nerves. The size of the CSNAP is a more sensitive measure compared to the CMAP in revealing the presence of distal sensorimotor axonopathy.

Pain survey was administered to 77 patients undergoing nerve conduction (NC) and needle electromyographic (EMG) procedures. The patient was asked to rate the pain immediately after the electrodiagnostic study was completed. Statistical analyses were performed to determine if there were relationships between pain and any of the technologic and physiologic variables. The findings revealed no significant correlation between age and pain from the NC or needle EMG procedure. The body mass index (BMI) also showed no correlation to pain from the procedures. Also, there was no correlation between pain and the EMG needle gauge or length. Pain from needle EMG was correlated with NC pain, and EMG was perceived as more painful than the NC procedure. Multiple regression analysis showed that age, sex, and needle size were not significantly related to pain from the EMG examination. Again, the age, sex, and BMI showed no significant relationship to pain from the NC test. From this survey, the individual's age, sex, habitus, and size of the EMG needle (to some extent) do not seem to influence significantly the perception of pain during electrodiagnostic procedures.

A 32-year-old man with myotonia congenita (Becker type) sustained multiple gunshot wounds. These produced a partial thoracic spinal cord injury and a severe sciatic nerve injury. Six days following the incident, clinical (percussion) and electrophysiologic (EMG) myotonia could be elicited in paretic leg muscles resulting both from the myelopathy and peripheral nerve disruption. Eight months later, the myotonia was no longer present in denervated muscles from the sciatic nerve injury, but was still noted in muscles with upper-motor neuron weakness from the myelopathy. Although myotonia is related principally to abnormalities in the muscle fiber itself, it appears that it is also dependent upon the structural integrity of the peripheral nerve supply to the muscle for myotonia to continue to occur. The findings in this patient suggest that myotonia may well have diminished and disappeared in muscles shortly after the nerves had undergone Wallerian degeneration. Myotonia does not recur if there is no significant reinnervation.

Sensory nerve conduction (NC) studies that were performed on patients with Guillain-Barre syndrome (GBS) were reviewed. These were compared with the sensory NC findings in patients with peripheral neuropathy of the axonal-loss type (axonopathies) and chronic inflammatory demyelinating polyneuropathy (CIDP). In GBS, the sural sensory nerve frequently showed normal NC findings compared to the median and ulnar sensory nerves. The reverse pattern was seen in axonopathies and CIDP, in which the sural nerve showed more abnormalities than the median and ulnar nerves. This pattern of sensory NC abnormalities may assist the examiner in differentiating GBS from other types of peripheral polyneuropathy.

The sensory nerve conduction study (NCS) is a sensitive means for demonstrating the localized median nerve dysfunction at the wrist in carpal tunnel syndrome (CTS). We reviewed the sensory NCS data of 102 patients (178 median nerves) with CTS and tried to determine if there were significant differences in the findings between the index and middle fingers. There was no statistically significant difference in the amplitudes of the compound sensory nerve action potentials (CSNAPs) recorded antidromically from the index and middle fingers during median nerve stimulation at the palm and wrist. Moreover, there was no statistically significant difference in the finger-to-palm and palm-to-wrist sensory nerve conduction velocities (CVs) between the index and middle fingers. The mean CSNAP amplitudes and mean sensory CVs were comparable in values from these two fingers and they showed a high and positive correlation. It appears that the sensory nerves to the index and middle fingers are compromised to a similar degree in CTS, and neither finger will reveal significantly more sensory conduction abnormalities than the other will.

Foot drop resulting from weakness of the anterior tibial muscle is commonly encountered in clinical practice. We analyzed the incidence of needle electromyographic (EMG) abnormalities in the anterior tibial and gastrocnemius muscles from traumatic injuries to the sciatic nerve and also from different non-traumatic lower motor neuron conditions. In both traumatic and non-traumatic cases, the anterior tibial muscle showed relatively more EMG abnormalities compared to the gastrocnemius. It appears that the anterior tibial muscle is more susceptible to injury from a variety of pathologic conditions, as opposed to the gastrocnemius muscle.

Supramaximal CMAPs to peroneal nerve stimulation at the knee were recorded from 5 locations on the anterior tibial muscle in 24 patients (30 muscles). The active recording locations were: midpoint of the muscle belly, at 4 cm distal and proximal to it, and at 2 cm lateral and medial to it. Reference electrode was at the medial malleolus. CMAP duration, amplitude, and area were measured, and ratios of their corresponding minimum to maximum values were computed. Thirteen patients (15 muscles) had normal nerve conduction and needle EMG studies. Mean ratios of minimum to maximum values were duration = 0.89, amplitude = 0.67, and area = 0.75. Eleven patients (15 muscles) had abnormal studies, and the mean ratios of minimum to maximum values were duration = 0.87, amplitude = 0.66, and area = 0.71. CMAP duration, unlike amplitude and area, appears least likely to be influenced by the recording electrode location, and is a more stable and reproducible measure during nerve conduction studies. The maximum (or minimum) values in the CMAP duration, amplitude, and area frequently do not coincide to one electrode recording location. A majority of the CMAPs recorded from different muscle locations had an initial negative phase, suggesting that the endplate zones of the anterior tibial muscle are dispersed rather than concentrated in a small region.

Supramaximal compound sensory nerve action potentials (CSNAPs) were recorded antidromically from five fingers of the same hand to electrical stimulation of the median, ulnar, and radial nerves in 17 normal subjects. The mean amplitudes of the median CSNAPs from the thumb, index, and middle fingers were similar in values. There was minimal radial sensory contribution to the thumb, with the mean radial CSNAP amplitude about one-fourth the size of the median CSNAPs. The mean median and ulnar CSNAP amplitudes from the ring finger were approximately half, and the mean ulnar CSNAP amplitude from the little finger was approximately 85%, of the median CSNAP amplitudes from the other fingers. The median, ulnar, and radial sensory nerve conduction velocities were close in values. There appears to be less variability in the population normative data when the size of the CSNAPs is expressed in terms of amplitude ratio rather than in absolute amplitude value.