Somatosensory evoked potentials from musculocutaneous nerve in the diagnosis of brachial plexus injuries

Correlation of Magnetic Resonance Imaging (Neurography) and Electrodiagnostic Study Findings with Intraoperative Findings in Post Traumatic Brachial Plexus Palsy

Background  The majority of brachial plexus injuries (BPIs) are caused by trauma; most commonly due to two-wheeler road accidents. It is important to determine whether the lesion in question is pre-ganglionic or post-ganglionic for purposes of surgical planning and prognosis. Diagnostic testing helps the surgeon to not only decide whether surgical intervention is required, but also in planning the procedure, thereby maximizing the patient's chances of early return to function. The aim of the study was to determine the diagnostic efficacy of electrodiagnostic studies (Edx) and magnetic resonance imaging (MRI) individually, and in unison, in detecting the type and site of BPI by comparison with intraoperative findings (which were used as the reference standard) in patients with posttraumatic BPI. Methods  It is an observational cross-sectional prospective randomized study, wherein 48 patients with BPI underwent a detailed clinical and neurological examination of the upper limb, Edx, MRI neurography and were subsequently operated upon. We assessed a total of 240 roots. The diagnosis of all spinal roots was noted on Edx. MRI was performed to look for root avulsion, pseudomeningocoele, and/or rupture injury. The patients were subsequently operated upon. All roots were traced from infraclavicular level right up to the foramen to ensure continuity of root or note rupture/ avulsion. The findings were tabulated. Results  MRI accurately diagnosed 138 of the 147 injured roots and MRI sensitivity for the detection of BPI was 93.88%, whereas Edx correctly identified 146 out of 147 injured roots and thus, had sensitivity of 99.32%; however, both lacked specificity (18.28 and 20.43%, respectively). With Edx and MRI in unison, sensitivity was 100% which meant that if a given patient with a BPI is subjected to both tests, not a single abnormal root will go unnoticed. Conclusion  Edx and MRI are two highly sensitive investigation modalities whose combined sensitivity is 100% for the detection of a root injury. Therefore, we recommend both tests as they are excellent screening tests.

Brachial plexus injuries: diagnosis performance and reliability of everyday tools

PURPOSE

Determining the patterns of brachial plexus injuries is challenging. Diagnostic methods have been used to facilitate diagnosis, but there is no consensus regarding which tool best complements physical examination (PE). Magnetic resonance imaging (MRI) and nerve conduction studies (NCSs) are instruments with widespread use and feasibility for everyday assessment. In this study, we evaluated the diagnostic performance of these diagnostic instruments and PE. We also assessed the agreement in the PE and diagnostic instrument findings of two experienced and certified hand surgeons.

METHODS

We reviewed data gathered from medical records and compared these data with the results of operative findings. We divided data according to the site of injury and the root injury patterns for all three diagnostic instruments (PE, MRI, and NCSs).

RESULTS

We considered 102 assessments. We found poor inter-observer agreement for the PE assessments and poor agreement among the PE, NCS, and MRI assessments. Diagnostic performance was higher for PE: sensitivity = 97.8 [95% confidence interval (C.I.) = 92.1-99.7]; specificity = 30.8 [95% C.I. = 9.1-61.4], and NCSs (sensitivity = 98.9 [95% C.I. = 93.9-100]; specificity = 23.1 [95% C.I. = 5-53.8]. MRI had inferior performance for all measurements. Separate analysis using pre- and post-ganglionic injuries revealed that PE had the lowest sensitivity, 46.7 (95% C.I. = 21.3-73.4) despite having the highest specificity, 81.6 (95% C.I. = 71.9-89.1).

DISCUSSION

Low agreement among the findings using different diagnostic instruments demonstrated that PE is the most specific tool, despite its low sensitivity. Detailed PE is cornerstone for evaluating brachial plexus injuries and NCSs are better than MRI for scrutinizing injuries not found in PE.

CLINICAL RELEVANCE

In our study, NCSs exhibited superior performance to MRI, and should be considered a more reliable supporting tool after detailed PE.

Dermatomal somatosensory evoked potentials in brachial plexus injuries

The dermatomally stimulated somatosensory evoked potential is an essentially painless, noninvasive procedure that can add useful information to the diagnosis of the site and extent of brachial plexus injuries. In this study, 13 patients with unilateral brachial plexus injuries who had previously undergone conventional electromyographic testing underwent somatosensory evoked potential recording with median, ulnar, radial, musculocutaneous nerve and C5, C6, C7, C8 and T1 dermatomal stimulation. There was no significant difference in the peak latencies, interpeak latencies, or amplitudes of the major peaks between the normal values and the values from the affected levels. However, analysis for absence or presence of major peaks from side-to-side was useful in supporting the data from electromyographic and radiologic studies, as well as in providing more specific information as to the level of injury and extent of injury in two of the cases. The accurate diagnosis can provide the information needed to determine patient treatment as well as plan the rehabilitation program of the patient. The dermatomal somatosensory evoked potential can be a useful supplement to the assessment of the patient with a brachial plexus injury.

Important abnormalities in recordings of somatosensory evoked potentials in coma

We have chosen six illustrations showing how much vital information can be obtained from median nerve SEPs during the first 24 hours in coma. With avulsion of brachial plexus roots there was loss of SEPs at the cervical cord and the scalp from the affected side. In a severe injury of the cervical cord there was preservation of brachial plexus potentials, while SEPs at the cervical cord were absent. After critical deterioration in a case of repeated subarachnoidal hemorrhage, scalp SEPs with very short latency occurred, which is a finding suggestive of destruction of cortical SEP generators heralding a fatal outcome. In a case of brain injury combined with central hyperthermia, there was initially a loss of scalp SEPs probably due to the combined effect of these factors. In a case of brain injury there were bifid peaks at the scalp level. It is important to assess central sensory conduction time only to the first scalp SEP, otherwise an erroneously abnormal state may be inferred. In a patient with clinical and EEG evidence of brain death there was a loss of far-field thalamic potentials at the neck. It is important to be aware of such presentations to be able to provide corroborative assurance for the assessment of prognosis.

Short latency somatosensory evoked potentials in patients with painful dysaesthesias in peripheral nerve lesions

Abnormally delayed and attenuated short latency somatosensory evoked potentials after electrical stimulation in the distribution of painful dysaesthesias after peripheral nerve lesions are reported in 4 selected patients with lesions in very proximal parts of the peripheral nerves. These included painful spondylopathic cervical radiculopathy, meralgia paraesthetica, pyriformis syndrome and allodynia after injury of the femoral nerve. Locally developed techniques for testing musculocutaneous, lateral femoral cutaneous and saphenous nerves were used in 3 patients. Possible pathophysiological mechanisms causing evoked potential abnormalities are discussed.

Somatosensory evoked potentials after stimulation of digital nerves in upper limbs: normative data

Normative data for somatosensory evoked potentials (SEPs) after stimulation of digital nerves from the first, third and fifth digits, which reach the spinal cord through C6, C7 and C8 roots are presented in 20 normal adults. SEP peak latencies and amplitudes are indicated for Erb's point, the level of the seventh and second cervical vertebrae and contralateral cortical hand area.

Validity of median nerve somatosensory evoked potentials in the diagnosis of supraclavicular brachial plexus lesions

Experience with median nerve SEPs in the diagnosis of brachial plexus lesions is analysed in 49 patients selected from a total material of 264 cases with brachial plexus problems tested by SEP techniques. Median nerve SEPs were always compared with the results of SEPs after stimulation of at least one other nerve relevant to the site of the lesion as suspected clinically and electromyographically. All patients presented with unilateral brachial plexus problems and all root lesions were verified by clinical presentation, EMG studies, myelogram or surgery. There were 19 brachial plexus injuries, 13 cases with cervical spondylopathic radiculopaties without myelopathy and 7 patients presented brachial plexopathy with systemic cancer. It was found that median nerve SEPs were always normal in injuries of upper trunk and root avulsions confined to one or two root levels. Median nerve SEPs were abnormal in multiple trunk lesions and multiple root avulsions. In patients with spondylopathic radiculopathies median nerve SEPs were normal apart from one case where involvement of multiple roots was present. Median nerve SEPs were useful in assessing patients presenting brachial plexus problems in the presence of systematic cancer apart from cases where lower trunk involvement was present. In general, median nerve SEPs are useful if they are combined with SEP testing of other nerves anatomically more closely related to the problem as outlined clinically and electromyographically.

Nervous propagation along 'central' motor pathways in intact man: characteristics of motor responses to 'bifocal' and 'unifocal' spine and scalp non-invasive stimulation

In 23 healthy adult volunteers motor action potentials (MAPs) were elicited in upper and lower limb muscles during stimulation of appropriate sites at spinal and scalp level, through skin electrodes. 'Bifocal' stimulation of scalp and spine motor tracts was performed with 2 plaques (3.5 cm2 each), delivering single pulses of 440-940 mA, less than 50 microseconds in duration, which elicited high voltage (up to 10 mV) MAPs in arm and leg muscles. 'Unifocal' stimulation of scalp was carried out through a cathode consisting in a belt or in a series of rectangular interconnected plaques secured around the head, 1-2 cm rostral to the nasion-inion plane, and in a circular anode placed on the appropriate scalp site. MAPs with similar amplitude-latency characteristics were recorded with both 'bifocal' and 'unifocal' stimulating methods. However, the 'unifocal' stimulation necessitated 5-10 times less current than the 'bifocal' one. The 'unifocal' device using the interconnected plaques (6-12 in number) provided the most tolerable stimuli with the lowest amount of current (60-106 mA, rectangular pulses of 100-150 microseconds). Conduction times and velocities of motor pathways in various 'central' and 'peripheral' districts were calculated. Voluntary contraction of target muscles remarkably enhanced MAP amplitudes during scalp, but not during spine stimulation. A nerve action potential was recorded from ulnar nerve during scalp stimulation. MAPs in hand muscles to scalp stimulation were obliterated by the simultaneous activation of the peripheral fibres innervating the target muscle, because of collision between ortho- and antidromically propagated motor impulses. Anodal stimuli showed liminal values significantly lower than the cathodal ones. Mapping studies have been carried out with 'unifocal' scalp stimulation by using different types of anode and of stimulus parameters.

Assessing sensory involvement in lower limb nerve lesions using somatosensory evoked potential techniques

Somatosensory evoked potential (SEP) investigations in 18 patients with lower limb lesions are summarized. Seven patients had problems involving the lateral femoral cutaneous nerve, four the femoral nerve, and seven the sciatic nerve. All lesions were unilateral. SEP techniques were accurate in meralgia paresthetica, and all five patients with demonstrable SEP abnormalities were successfully treated surgically. Delayed recovery of sensory function was shown in two patients with femoral nerve lesions and two patients with sciatic nerve lesions. In patients with sensory symptoms, only an SEP abnormality confined to the nerve distribution provides evidence of a lesion in the sensory pathways and helps to exclude psychologic causes. In a case of peripheral nerve Schwannoma, the presence of a small delay in a case of peripheral SEP supported the preoperative assessment that the tumor was not intrinsic in nature, and this was confirmed at surgery and on subsequent full recovery. The SEP technique allows quantitative assessment of sensory nerve conduction through the peripheral neuron and centripetal pathways.

Comparison of cervical SEPs on median, radial and ulnar nerve stimulation

Cervical responses (SEPs) to stimulation of the median, radial and ulnar nerves were studied in 9 healthy subjects. In recordings from e Cv7 electrode referenced to a scalp electrode P11 presented a bilobed (P11a + P11b) profile for all three nerves whereas from Cv2 only P11b appeared as a rule. P11a and P11b were more distinct in the ulnar than in the median and radial nerves. The P11 onset-P13 onset interval was virtually the same for the radial and median nerves and approximately 0.4 msec longer for the ulnar nerve. This difference probably represents the Cv8 to Cv6 intramedullary conduction time. An exact evaluation of P11 onset is possible only in low cervical recordings, though the P11 peak may be a useful landmark when recording from Cv2. P11a would appear to originate at (or near) spinal entry, P11b high in the cervical cord and P13 at supraspinal level.