Anterior interosseous nerve conduction study: normative data

Nerve conduction study on the split-hand plus index in Amyotrophic lateral sclerosis: correlations with lower motor neuron impairment

INTRODUCTION

In the arms of patients with Amyotrophic lateral sclerosis (ALS) two peculiar patterns of dissociated muscular atrophy have been described: the split-hand sign (with predominant atrophy of the lateral aspect of the hand, compared to hypothenar eminence) and the split-hand-plus sign (SHPS), a predominant abductor pollicis brevis (ABP) atrophy with sparing of flexor pollicis longus (FPL).

AIMS

In this case-control study, we evaluated the diagnostic utility of a neurophysiological indicator of SHPS and assessed its association with clinical features.

METHODS

We prospectively studied 59 incident ALS patients, 61 patients with ALS-mimic disorders (OND) and 61 non-neurological controls (NNCs). ABP and FPL compound muscle action potentials (CMAP) amplitudes were obtained by supramaximal stimulation of median nerve at elbow. Split-hand plus index (SHPI) was calculated according to the formula: APB-CMAP/FPL-CMAP.

RESULTS

SHPI was significantly lower in ALS compared to OND patients and NNCs (p < 0.0001). SHPI value < 1 was observed in 2% of NNCs and 9% of OND patients and demonstrated an accuracy of 71% in differentiating ALS from OND and an accuracy of 74% in differentiating ALS from NNC. SHPI was associated with higher LMN score, and higher disease severity as quantified by the ALSFRS-r.

CONCLUSION

Our results indicate that SHPI is a reliable indicator to distinguish ALS patients from ONDs and NNCs. SHPI was significantly associated to the degree of lower motor neuron impairment but showed no association with upper motoneuron impairment.

Isolated Palsy of the Anterior Interosseous Nerve to Flexor Pollicis Longus, Magnetic Resonance Imaging and Clinical Correlation: A Case Report

CASE

Anterior interosseous nerve (AIN) palsy is an uncommon, though well-described, clinical entity. When isolated to the thumb, it can be confused with atraumatic rupture of the flexor pollicis longus (FPL) tendon. A 57-year-old man experienced atraumatic onset of difficulty flexing the distal interphalangeal thumb joint. Magnetic resonance imaging (MRI) demonstrated denervation edema of the FPL, suggesting atypical AIN palsy. Resolution of symptoms and MRI findings occurred concomitantly with nonoperative treatment.

CONCLUSION

Atypical AIN palsy limited to the FPL is a rare clinical entity whose diagnosis can be supported with MRI. Here, we report a successful case of nonoperative management.

Electrodiagnostic Assessment of Uncommon Mononeuropathies

Carpal tunnel syndrome, ulnar neuropathy at the elbow, and peroneal neuropathy are the most common mononeuropathies; however, other individual nerves may also be injured by various processes. These uncommon mononeuropathies may be less readily diagnosed owing to unfamiliarity with the presentations and vague symptoms. Electrodiagnostic studies are essential in the evaluation of uncommon mononeuropathies and can assist in localization and prognostication. However, they can also be challenging; stimulation at the proximal sites is difficult and well-validated reference values are not available. This article reviews the electrodiagnostic assessment of several uncommon upper and lower extremities mononeuropathies.

Pseudo-Anterior Interosseus Nerve Syndrome: A Case Report and a Review of Clinical Signs, Pathology and Functional Anatomy of the Precision Grip

Precision grip, a prehensile function of humans, is exacted through the action of the median nerve and its main tributary, the anterior interosseus nerve (AIN). In the forearm, the AIN can be subject to nerve entrapment by tendinous and fibrous arches or accessory and variant muscles. It is also vulnerable to trauma of the upper arm and forearm. To the neurologist, an isolated neuritis or an immune-mediated medial cord or lower trunk brachial plexopathy (Parsonage-Turner syndrome) is the usual mode of presentation. When the spread of muscle weakness is beyond the territory of the AIN, the syndrome is referred to as a pseudo-AIN. The AIN is grouped into fascicles that are compartmentalized separately from the median nerve proper, and trauma in the upper arm may selectively involve the AIN. We present a case of pseudo-AIN following elbow arthroscopic surgery and outline the pathology, clinical signs, and functional anatomy of the AIN and the precision grip.

Cortical hyperexcitability and the split-hand plus phenomenon: pathophysiological insights in ALS

Preferential involvement of thenar muscles compared to flexor pollicis longus (FPL), termed 'the split-hand plus sign', appears to be a clinical feature of amyotrophic lateral sclerosis (ALS). In an attempt to understand the pathophysiological mechanisms underlying this clinical phenomenon, threshold tracking transcranial magnetic stimulation techniques were utilized to assess whether cortical mechanisms may be a significant contributing influence. Cortical excitability studies were undertaken on 17 ALS patients, with motor evoked potentials (MEP) recorded from thenar muscles and FPL. Split-hand plus index (SHPI) was derived by dividing motor amplitudes recorded over APB with those recorded over FPL. Results showed the SHPI was significantly reduced in ALS (SHPIALS 0.87 ± 0.12; SHPICONTROLS 1.7 ± 0.2, p < 0.001). Cortical studies disclosed significant increases in MEP amplitudes recorded over thenar muscles (p < 0.05) but not FPL (p = 0.11), and were significantly correlated with the SHPI (R = -0.83, p < 0.01). The cortical silent period duration was reduced from thenar muscles (p < 0.01). Although there was a ubiquitous reduction in short-interval intracortical inhibition (APB, p < 0.01; FPL < 0.05), this reduction was more prominent over the thenar muscles. In conclusion, findings from the present study suggest that cortical dysfunction in the form of hyperexcitability contributes to the pathophysiological basis of the split-hand plus sign in ALS.

Cortical excitability differences between flexor pollicis longus and APB

Although abductor pollicis brevis (APB) and flexor pollicis longus (FPL) share a common peripheral nerve supply, these muscles subserve different functions and may be differently affected in neurodegenerative disease such as amyotrophic lateral sclerosis (ALS). As a consequence, differences in cortical excitability may potentially develop in relation to these functional differences. Cortical excitability was assessed using the threshold tracking transcranial magnetic stimulation (TMS) technique in 15 healthy controls with motor responses recorded over the APB and FPL using surface electrode recordings. Short-interval intracortical inhibition (SICI) was significantly reduced from the FPL compared to APB (SICIFPL 6.9±1.8%; SICIAPB 10.7±1.4%, P<0.01). In addition, the FPL motor evoked potential amplitude (MEPFPL 14.7±2.3%; MEPAPB 21.7±3.9%; P<0.01) and cortical silent period duration (CSPFPL 174.7±6.7ms; CSPAPB 205.4±3.9ms, P<0.01) were significantly smaller. The findings in the present study indicate that cortical inhibition and corticomotoneuronal output is reduced when recording over the FPL. The differences in cortical excitability may develop as a consequence of varied function and could potentially explain the dissociated muscle atrophy evident in ALS.

Compression and entrapment neuropathies

Peripheral nerve entrapments are frequent. They usually appear in anatomical tunnels such as the carpal tunnel. Nerve compressions may be due to external pressure such as the fibular nerve at the fibular head. Malignant or benign tumors may also damage the nerve. For each nerve from the upper and lower limbs, detailed clinical, electrophysiological, imaging, and therapeutic aspects are described. In the upper limbs, carpal tunnel syndrome and ulnar neuropathy at the elbow are the most frequent manifestations; the radial nerve is less frequently involved. Other nerves may occasionally be damaged and these are described also. In the lower limbs, the fibular nerve is most frequently involved, usually at the fibular head by external compression. Other nerves may also be involved and are therefore described. The clinical and electrophysiological examination are very important for the diagnosis, but imaging is also of great use. Treatments available for each nerve disease are discussed.

Electrodiagnostic evaluation of ulnar neuropathy and other upper extremity mononeuropathies

Upper extremity mononeuropathies are some of the common disorders seen in neurophysiology laboratories. Electrophysiologic studies rely on accurate localization based on knowledge of applicable anatomy and features of history and physical examination. Careful electrodiagnostic studies provide an accurate diagnosis, help localize the lesion site, exclude alternate diagnoses, reveal unsuspected diagnoses, determine pathophysiology of lesions, and assess severity, timeframe, and prognosis of lesions. This article discusses the electrodiagnostic approach to ulnar neuropathy, proximal median neuropathy, radial neuropathy, musculocutaneous neuropathy, axillary neuropathy, suprascapular neuropathy, and long thoracic neuropathy. Pertinent aspects of the history and physical examination, nerve conduction studies, and electromyography are presented.