Two-step technique to optimize the medial antebrachial cutaneous nerve response

ObjectivePosition of recording electrodes for the antidromic sensory-nerve conduction study (SCS) of the medial antebrachial cutaneous (MABC) nerve is conventionally determined according to the anatomical landmarks. However, the variation of its nerve course may interfere with accurate placement. In this study, we aimed to test how the systematic two-step examination, an orthodromic–antidromic series, affects the results.MethodsSubjects were 40 arms from 20 control subjects. For the two-step method, we first searched for the minimal threshold point over the forearm using the orthodromic technique. The recording electrode for the antidromic SCS was placed over the optimal point determined in this way.ResultsThe SNAP amplitude by our two-step method was 1.39 times (range 0.99–3.94) of that by the conventional method. Four out of 20 subjects showed greater than 50% (up to 83%) interside difference of the SNAP amplitude by the conventional methods, whereas the maximal interside difference was 38% by the two-step method.ConclusionsCareful adjustment of the recording position using the two-step method would contribute to an accurate evaluation of the MABC nerve.SignificanceTo determine the recording position solely based on anatomical landmarks may cause erroneously abnormal interside difference for this nerve.     

Posterior antebrachial cutaneous nerve conduction study in radial neuropathy

Radial neuropathy most commonly occurs as a result of external compression at the spiral groove region. The posterior antebrachial cutaneous nerve (PACN) conduction study was performed in 15 consecutive patients with radial palsy. Unilateral PACN abnormalities were present in 11 patients. A normal PACN study was correlated with clinical improvement at 3 months. Conversely, PACN abnormality was correlated with radial motor axon loss and a poorer prognosis. The PACN study is a simple adjunct which provides additional information relating to the diagnosis and prognosis of radial lesions.     

Posterior antebrachial cutaneous nerve conduction studies in normal subjects.

OBJECTIVE: The posterior antebrachial cutaneous (PABC) nerve is a sensory nerve that branches out from the radial nerve at the level of the spiral groove. Thus it can be affected in a radial nerve lesion at or proximal to its origin in the spiral groove. However, there has been limited knowledge about the normal values of PABC nerve conduction studies. This study was done to determine these normal values. METHODS: Sixty-three healthy adults (23 males) with a mean age of 41.5+/-10.6 (range, 20-90) years were recruited with informed consent. A total of 126 nerves were studied. The nerve conduction studies were performed using a Dantec Counterpoint EMG machine (Dantec, Skovlunde, Denmark). RESULTS: The mean+/-standard deviation values for the onset as well as peak latency, conduction velocity, amplitude and side-to-side amplitude ratio were 2.07+/-0.16 (range, 1.80-2.60) ms, 2.35+/-0.15 (range, 2.05-2.90) ms, 58.21+/-4.29 (range, 46.15-66.67) m/s, 6.10+/-2.11 (range, 2.90-13.00) microV and 0.83+/-0.12 (range, 0.60-0.99), respectively. There was a significant correlation between the subject age and the PABC onset and peak latencies as well as the amplitudes. CONCLUSIONS: The PABC nerve is assessable for nerve conduction studies and these normal values may be useful in evaluation of patients with suspected radial nerve lesions.     

A case of isolated tuberculoid leprosy of antebrachial medial cutaneous nerve

Abstract. Leprosy is an infectious disease of prevalence still high in endemic areas in Brazil. The neurological presentation depends on the involved nerve and is usually associated with skin lesions and the formation of multiple abscesses. We present a case of isolated tuberculoid leprosy, discuss the occurrence, the differential diagnosis and the treatment of this rare presentation and reaffirm the importance of considering leprosy in the differential diagnosis of patients with polyneuropathy or nerve enlargement with no skin lesions.     

The medial antebrachial cutaneous nerve: antidromic and orthodromic conduction studies

Medial antebrachial cutaneous nerve (MABCN) conduction studies were performed antidromically and orthodromically in 70 control subjects to determine normal values and define the lower limits of normality. The mean sensory action potential (SAP) amplitudes were 17.7 and 17.5 microV and the sensory conduction velocities were 60 and 61 m/s, respectively, with the antidromic and orthodromic techniques. With both techniques, no SAP amplitude was lower than 6 microV. The lower limits of normal of the interside amplitude ratio were 1.66 when both techniques were used and 2.0 when only one was used.     

A new pitfall in a sensory conduction study of the lateral antebrachial cutaneous nerve: Spread to the radial nerve

Introduction: We describe a previously unreported pitfall, spread of the stimulus at the elbow to the radial nerve, in an antidromic sensory nerve conduction study of the lateral antebrachial cutaneous (LAC) nerve. Methods: Subjects consisted of 80 healthy volunteers, and both sides were examined for each subject. Besides routine recording of the LAC nerve, sensory nerve action potentials (SNAPs) of the radial nerve were recorded distally. Results: The spread phenomenon occurred in 73 of 160 arms (46%), and the SNAP amplitude increased due to contamination of the radial SNAP up to 6.7 times the genuine LAC SNAP. In 10 arms (6%), the spread started before the LAC SNAP was saturated, and the genuine LAC SNAP was unknown due to an anatomical variation in at least 1 arm. Conclusions: Without monitoring distal radial SNAPs, the spread phenomenon will remain unrecognized. This pitfall undermines the reliability of the test. Muscle Nerve 50:186–192, 2014     

Brachial plexus neoplastic lesions assessed by conduction study of medial antebrachial cutaneous nerve.

Two cases of neoplastic involvement of the lower brachial plexus are reported. This condition was due to recurrence of lymphoma in one case and to axillary node spread of breast cancer in the other. The neuropathic origin and the location of the lesion in the lower brachial plexus between the T-1 root and the axilla was demonstrated by the presence of abnormalities on testing of the medial antebrachial cutaneous nerve in the symptomatic upper limb and comparing it to the healthy one. All other electrodiagnostic tests were normal. Such a finding suggests the need for imaging of the lower brachial plexus region by computed tomography or magnetic resonance imaging.     

Pressure neuropathy of the posterior femoral cutaneous nerve

Neuropathy of the posterior femoral cutaneous nerve by compression is described in three cases. The case history and the physical examination are the most important clues to diagnoses.     

Lateral antebrachial cutaneous neuropathy in a windsurfer.

Lateral antebrachial cutaneous neuropathy (LACN) was diagnosed in a young woman who developed pain and paresthesias in the right forearm after a long day of windsurfing (board sailing). The symptoms resolved with conservative treatment, including cessation of windsurfing and a brief course of oral corticosteroids. There was a permanent residual cutaneous sensory deficit in the distribution of the LACN. LACN is important to recognize because the symptomatology may mimic pathology of a cervical root, the brachial plexus, and the radial and median nerves at the level of the elbow.     

Iatrogenic vertebral artery injury

Iatrogenic vertebral artery injury (VAI) results from various diagnostic and therapeutic procedures. The objective of this article is to provide an update on the mechanism of injury and management of this potentially devastating complication. A literature search was conducted using PubMed. The iatrogenic VAIs were categorized according to each diagnostic or therapeutic procedure responsible for the injury, i.e., central venous catheterization, cervical spine surgery, chiropractic manipulation, diagnostic cerebral angiography, percutaneous nerve block, and radiation therapy. The incidence, mechanisms of injury, and reparative procedures were discussed for each type of procedure. The type of VAI depends largely on the type of procedure. Laceration was the dominant type of acute injury in central venous catheterization and cervical spine surgery. Arteriovenous fistulae and pseudoaneurysms were the delayed complications. Arterial dissection was the dominant injury type in chiropractic manipulation and diagnostic cerebral angiography. Inadvertent arterial injection caused seizures or stroke in percutaneous nerve block. Radiation therapy was responsible for endothelial injury which in turn resulted in delayed stenosis and occlusion of the vertebral artery (VA). The proximal VA was the most vulnerable portion of the artery. Although iatrogenic VAIs are rare, they may actually be more prevalent than had previously been thought. Diagnosis of iatrogenic VAI may not always be easy because of its rarity and deep location, and a high level of suspicion is necessary for its early detection. A precise knowledge of the surgical anatomy of the VA is essential prior to each procedure to prevent its iatrogenic injury.     

Two modes of cutaneous reinnervation following peripheral nerve injury.

The return of sensation to the foot following sciatic nerve crush injury was analyzed behaviorally and electrophysiologically in the rat. Functional recovery begins within four days. Its early phase is accounted for by expansion of the functional distribution of intact neighboring fibers of the saphenous n. It occurs even if the sciatic n. is ligated, and it disappears with section of the saphenous n. Accompanying this functional expansion we began to encounter in electrophysiological recordings from the saphenous n., fibers with unusually large receptive fields (RF's) extending onto the plantar surface of the foot, well beyond their limits in intact rats. All of the expanded RF's were high threshold mechanoreceptors. On about the twentieth day after crushing, the regenerating sciatic n. began to make a functional contribution. This was seen by return of sensation to zones not invaded by the saphenous n. and by the onset of sensation in rats in which the saphenous n. had previously been ligated. With return of the sciatic n. the expanded distribution of the saphenous n. went back to its original boundaries. Correspondingly, we could no longer find expanded saphenous n. RF's. We conclude that cutaneous reinnervation begins with the collateral expansion of high threshold afferents from intact neighboring nerves. This alien innervation is later replaced upon regeneration of the original nerve.     

Medial antebrachial cutaneous nerve conduction study, a new tool to demonstrate mild lower brachial plexus lesions. A report of 16 cases.

OBJECTIVE: This was to demonstrate the ability to electrodiagnosed mild lower brachial plexus lesion only through abnormal medial antebrachial cutaneous nerve (MABCN) conduction study. METHODS: We report 16 cases of unilateral, atypical pains and paresthesias of the upper limbs without motor deficit or atrophy. Patients were referred as carpal tunnel syndrome in 12 cases. All patients had needle examination of the impaired upper limb from C5 to T1. Motor and sensory conductions of median and ulnar nerves were bilaterally studied. MABCN was antidromically (16 cases) and orthodromically (9 cases) studied at the elbow in the both sides. MABCN abnormality was defined by an interside amplitude ratio of the sensory nerve action potential equal or greater than 2 (mean + 3 SD). RESULTS: No patient had a definitive and accurate diagnosis, before MABCN abnormality determination. MABCN testing was abnormal in all the 16 cases with a mean interside amplitude ratio of 7.2 (mean + 25 SD), when all other motor and sensory nerve conductions were normal. All except four patients showed normal needle examination from C5 to T1. In 5 cases, an obvious cause (traumatic and neoplastic) explained the mild lower brachial plexus lesion. In 2 cases, a mild neurogenic thoracic outlet syndrome (NTOS) was confirmed by surgical findings. In the 9 other cases, the mild lower brachial plexus lesion defined by MABCN findings, was without cause and was considered as a mild NTOS. CONCLUSIONS AND SIGNIFICANCE: These 16 cases, support a new electrodiagnostic pattern to define a mild lower brachial plexus lesion: comparatively low or low MABCN SNAP amplitude, normal median and ulnar SNAP/Compound motor action potential amplitudes and normal or slightly reduced interference pattern in some C8-T1 innervated muscles. This pattern can be found in patients with 'carpal tunnel syndrome like' symptoms who have normal electro-diagnostic examination, or in patients with clinical features suggesting a lower brachial plexus lesion.     

Anterior femoral cutaneous nerve injury following femoral artery reconstructive surgery.

Two cases are presented exhibiting symptoms and signs of bilateral anterior femoral cutaneous nerve injury, clinically sparing femoral nerve branches to the saphenous nerve and quadriceps muscles. This occurred following surgical dissection in the femoral triangles associated with femoral artery reconstructive surgery. Anterior femoral cutaneous nerve injury should be considered when anterior medial thigh pain and numbness occur following aortofemoral bypass graft surgery and other types of femoral artery reconstructive surgery.     

Natural history of sensory nerve recovery after cutaneous nerve injury following foot and ankle surgery

Cutaneous nerve injury is the most common complication following foot and ankle surgery. However, clinical studies including long-term follow-up data after cutaneous nerve injury of the foot and ankle are lacking. In the current retrospective study, we analyzed the clinical data of 279 patients who underwent foot and ankle surgery. Subjects who suffered from apparent paresthesia in the cutaneous sensory nerve area after surgery were included in the study. Patients received oral vitamin B12 and methylcobalamin. We examined final follow-up data of 17 patients, including seven with sural nerve injury, five with superficial peroneal nerve injury, and five with plantar medial cutaneous nerve injury. We assessed nerve sensory function using the Medical Research Council Scale. Follow-up immediately, at 6 weeks, 3, 6 and 9 months, and 1 year after surgery demonstrated that sensory function was gradually restored in most patients within 6 months. However, recovery was slow at 9 months. There was no significant difference in sensory function between 9 months and 1 year after surgery. Painful neuromas occurred in four patients at 9 months to 1 year. The results demonstrated that the recovery of sensory function in patients with various cutaneous nerve injuries after foot and ankle surgery required at least 6 months.     

Identity of myelinated cutaneous sensory neurons projecting to nocireceptive laminae following nerve injury in adult mice

It is widely thought that, after peripheral injury, some low‐threshold mechanoreceptive (LTMR) afferents “sprout” into pain‐specific laminae (I–II) of the dorsal horn and are responsible for chronic pain states such as mechanical allodynia. Although recent studies have questioned this hypothesis, they fail to account for a series of compelling results from single‐fiber analyses showing extensive projections from large‐diameter myelinated afferents into nocireceptive layers after nerve injury. Here we show that, in the thoracic spinal cord of naïve adult mouse, all myelinated nociceptors gave rise to terminal projections throughout the superficial dorsal horn laminae (I–II). Most (70%) of these fibers had large‐diameter axons with recurving flame‐shaped central arbors that projected throughout the dorsal horn laminae I–V. This morphology was reminiscent of that attributed to sprouted LTMRs described in previous studies. After peripheral nerve axotomy, we found that LTMR afferents with narrow, uninflected somal action potentials did not sprout into superficial laminae of the dorsal horn. Only myelinated noiceptive afferents with broad, inflected somal action potentials were found to give rise to recurving collaterals and project into superficial “pain‐specific” laminae after axotomy. We conclude that the previously undocumented central morphology of large, myelinated cutaneous nociceptors may very well account for the morphological findings previously thought to require sprouting of LTMRs. J. Comp. Neurol. 508:500–509, 2008. © 2008 Wiley‐Liss, Inc.     

Medial antebrachial cutaneous sensory studies in the evaluation of neurogenic thoracic outlet syndrome

Over 3 years, we studied 8 patients with neurogenic thoracic outlet syndrome (TOS) and tested the medial antebrachial sensory response (MASR) to determine its diagnostic value. The MASR and ulnar sensory response (USR) were abnormal in all 8 patients. Seven had a low median motor response (MMR) with a low USR. In 1, the MASR and USR were abnormal but the MMR was normal. We conclude that the MASR is of diagnostic value in patients with neurogenic TOS. © 1998 John Wiley & Sons, Inc. Muscle Nerve 21:647–649, 1998.     

Crush injury to peripheral nerve

Summary Electron microscope observation were made of rat peroneal nerve after crushing using intravenously injected horseradish peroxidase (HRP) as a tracer protein to indicate changes in vascular permeability. At 1/2 h and 2 d after the crush there was gross leakage of HRP from damaged capillaries at the site of injury but none from vessels above or below this. Ultrastructurally vessels at the site of crush showed broken and separated endothelial cells. Proximally and distally there was little abnormal in the vessel walls; vesicles containing HRP were absent and tight-junctions between cells remained intact. Twenty-one days after the crush, leakage of HRP was found both at the site of crush and along the distal segment. The only change in vessel walls was an obvious increase in vesicles filled with HRP. Tracer was also found both in perivascular locations and throughout the endoneurial space.