AAEM case report #25: anterior interosseous nerve syndrome

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.

Anterior Interosseous Nerve Syndrome

Anterior interosseous nerve syndrome (AINS) is a rare form of peripheral neuropathy which involves disruption of the anterior interosseous nerve. The pathophysiology of AINS remains unclear. AINS typically initially presents with forearm pain and may gradually progress to palsy of the deep muscles of the anterior forearm. Diagnosis of AINS requires thorough patient history and physical exam. EMG is the preferred diagnostic study and classically reveals abnormal activity and prolonged latency periods within the evoked action potentials of the FPL and PQ. Due to the self-limiting nature of AINS, there is general agreement that conservative and symptomatic management should be explored for up to 6 months as first line therapy, which usually includes analgesics and nonsteroidal anti-inflammatory drugs, contracture prevention, hand therapy, and hand splinting. Surgical options such as internal neurolysis and minimally invasive endoscopic decompression may be explored if functional recovery from conservative management is limited.

Safety Window for the Volar Needle Approach for Examination of the Pronator Quadratus Using Ultrasonography

OBJECTIVES

To investigate pronator quadratus (PQ) anatomy and determine the proper volar needle insertion point based on landmarks, the tip of the ulnar styloid (an imaginary vertical line passing the tip of the ulnar styloid process [U line]), and the ulnar margin of the palmaris longus tendon (uPL) using ultrasonography.

DESIGN

Descriptive study.

SETTING

Department of physical medicine and rehabilitation.

PARTICIPANTS

Participants between 20 and 60 years without any diseases. (N=25; 13 men, 12 women; 50 forearms).

INTERVENTIONS

Ultrasonography.

MAIN OUTCOME MEASURES

The proximal and distal volar surface points of origin, the proximal and distal insertion sites, and the midpoint of the PQ (PQ_M) were determined. The distance of each of the PQ surface indices from the U line was measured, and the probe was positioned at the level of PQ_M parallel to the U line. The relative distances from the vertical surface points of the median nerve and ulnar artery to the uPL were measured.

RESULTS

The mean age and body mass index were 32.7±10.4 years and 21.98±2.83kg/m². The PQ_M was located at a mean distance of 2.63±0.35cm proximal from the U line (men 2.79±0.37cm and women 2.45±0.21cm; P<.05). The mean safety window for the volar approach was 0.72±1.8cm toward the radial side and 1.51±0.30cm toward the ulnar side from the uPL. The PQ was at a mean depth of 1.30±0.19cm from the skin and had a mean thickness of 1.19±0.24cm at the level of PQ_M. The distance between the U line and the proximal edge of the PQ, as well as the PQ thickness, was greater in men than in women.

CONCLUSIONS

The volar approach for needle electromyographic examination of the PQ can be performed precisely and safely.

Occupational mononeuropathies in industry

Peripheral nerve injuries have the potential to cause significant disability and can be commonly associated with recreational and occupational activities. Acute nerve injuries are mainly related to violent trauma, while repeated mechanical trauma due to external forces or repetitive motions can produce chronic nerve compression injury. This chapter will present a narrative review of the existing evidence of the association between peripheral compressive nerve disorders and work-related risk factors. Carpal tunnel syndrome (CTS) is the most common peripheral neuropathy in the general population and in working populations employed in manual repetitive and forceful activities. The work-relatedness of CTS is essentially based on epidemiologic evidence and the results of experimental studies showing the capability of repetitive wrist extreme postures, associated with hand-wrist forceful exertions, to increase the pressure inside the carpal tunnel and to compress the median nerve. Assembly industry, food processing and packaging, hand-arm vibrating tools, and jobs involving high-repetition, high-force tasks put workers at risk for CTS. Less strong evidence exists of the association between ulnar elbow neuropathy and manual tasks or repetitive stretch on squatting and peroneal nerve neuropathy at the fibular head. Very few reports are available about the association between occupation and other compressive peripheral nerve injuries.

Impacts of differences in epidemiological case definitions on prevalence for upper-extremity musculoskeletal disorders

OBJECTIVE

The aim of this study was to systematically evaluate prevalence based on variations in case definitions used for epidemiological studies of musculoskeletal disorders (MSDs).

BACKGROUND

Prior studies of MSDs have mostly relied on a single case definition based on questionnaires.

METHOD

In a multicenter prospective cohort study, we systematically collected data to evaluate impacts of differences in case definitions of MSDs on prevalence of three common musculoskeletal disorders: (a) shoulder tendinosis, (b) lateral epicondylalgia, and (c) carpal tunnel syndrome. Production workers were from 21 employment settings in three diverse U.S. states and performed widely varying work. All workers completed laptop-administered structured interviews, two standardized physical examinations, and nerve conduction studies (NCS). Case definitions included symptoms only, and symptoms plus physical examinations and/or NCS.

RESULTS

A total of 1,227 subjects had complete health data at baseline. The prevalence for shoulder tendinosis is 23.0% if only glenohumeral pain is used for a case definition, compared with 8.0% if a combination of pain plus a positive supraspinatus test is used. The prevalence for lateral epicondylalgia varied on the basis of lateral elbow pain (12.0%), pain plus tenderness on palpation (9.9%), or pain plus tenderness on palpation plus resisted wrist or middle finger extension (3.5%). Carpal tunnel syndrome prevalence varied on the basis of tingling or numbness in a median nerve-served digit (29.9%) or tingling or numbness plus NCS abnormalities consistent with carpal tunnel syndrome (9.0%).

CONCLUSION

Variations in epidemiological case definitions have major impacts on prevalence of common MSDs. Wide-ranging differences in prevalence may have impacts on purported risk factors that need to be determined.

Anterior interosseous nerve syndrome: fascicular motor lesions of median nerve trunk

Objective:

We sought to determine lesion sites and spatial lesion patterns in spontaneous anterior interosseous nerve syndrome (AINS) with high-resolution magnetic resonance neurography (MRN).

Methods:

In 20 patients with AINS and 20 age- and sex-matched controls, MRN of median nerve fascicles was performed at 3T with large longitudinal anatomical coverage (upper arm/elbow/forearm): 135 contiguous axial slices (T2-weighted: echo time/repetition time 52/7,020 ms, time of acquisition: 15 minutes 48 seconds, in-plane resolution: 0.25 × 0.25 mm). Lesion classification was performed by visual inspection and by quantitative analysis of normalized T2 signal after segmentation of median nerve voxels.

Results:

In all patients and no controls, T2 lesions of individual fascicles were observed within upper arm median nerve trunk and strictly followed a somatotopic/internal topography: affected were those motor fascicles that will form the anterior interosseous nerve further distally while other fascicles were spared. Predominant lesion focus was at a mean distance of 14.6 ± 5.4 cm proximal to the humeroradial joint. Discriminative power of quantitative T2 signal analysis and of qualitative lesion rating was high, with 100% sensitivity and 100% specificity (p < 0.0001). Fascicular T2 lesion patterns were rated as multifocal (n = 17), monofocal (n = 2), or indeterminate (n = 1) by 2 independent observers with strong agreement (kappa = 0.83).

Conclusion:

It has been difficult to prove the existence of fascicular/partial nerve lesions in spontaneous neuropathies using clinical and electrophysiologic findings. With MRN, fascicular lesions with strict somatotopic organization were observed in upper arm median nerve trunks of patients with AINS. Our data strongly support that AINS in the majority of cases is not a surgically treatable entrapment neuropathy but a multifocal mononeuropathy selectively involving, within the main trunk of the median nerve, the motor fascicles that continue distally to form the anterior interosseous nerve.

Diltiazem in the treatment of calcinosis in juvenile dermatomyositis

Subcutaneous calcifications occur in a variety of diseases, including juvenile dermatomyositis. These calcifications cause disabling symptoms that do not always respond to immunosuppressant therapy. The calcium antagonist diltiazem reduces subcutaneous calcifications in CREST syndrome and in isolated cases of children with dermatomyositis. Our study was performed to determine the effects of diltiazem when used as adjunctive therapy in children with dermatomyositis.

The WISTAH hand study: a prospective cohort study of distal upper extremity musculoskeletal disorders

Background

Few prospective cohort studies of distal upper extremity musculoskeletal disorders have been performed. Past studies have provided somewhat conflicting evidence for occupational risk factors and have largely reported data without adjustments for many personal and psychosocial factors.

Methods/design

A multi-center prospective cohort study was incepted to quantify risk factors for distal upper extremity musculoskeletal disorders and potentially develop improved methods for analyzing jobs. Disorders to analyze included carpal tunnel syndrome, lateral epicondylalgia, medial epicondylalgia, trigger digit, deQuervain’s stenosing tenosynovitis and other tendinoses. Workers have thus far been enrolled from 17 different employment settings in 3 diverse US states and performed widely varying work. At baseline, workers undergo laptop administered questionnaires, structured interviews, two standardized physical examinations and nerve conduction studies to ascertain demographic, medical history, psychosocial factors and current musculoskeletal disorders. All workers’ jobs are individually measured for physical factors and are videotaped. Workers are followed monthly for the development of musculoskeletal disorders. Repeat nerve conduction studies are performed for those with symptoms of tingling and numbness in the prior six months. Changes in jobs necessitate re-measure and re-videotaping of job physical factors. Case definitions have been established. Point prevalence of carpal tunnel syndrome is a combination of paraesthesias in at least two median nerve-served digits plus an abnormal nerve conduction study at baseline. The lifetime cumulative incidence of carpal tunnel syndrome will also include those with a past history of carpal tunnel syndrome. Incident cases will exclude those with either a past history or prevalent cases at baseline. Statistical methods planned include survival analyses and logistic regression.

Discussion

A prospective cohort study of distal upper extremity musculoskeletal disorders is underway and has successfully enrolled over 1,000 workers to date.

Anterior interosseous nerve compression syndrome: is there a role for endoscopy?

BACKGROUND

Anterior interosseous nerve syndrome is characterized by paralysis of the flexor digitorum profundus, the flexor pollicis longus and the pronator quadratus muscles without sensory loss. Extended exploration of the anterior interosseous nerve is the surgical treatment of choice. The present study evaluates the feasibility of an endoscopic approach for nerve decompression.

METHODS

Preparation of the anterior interosseous nerve was performed in ten human cadaver arms. Subsequently, one female patient suffering from anterior interosseous nerve syndrome was endoscopically operated on.

FINDINGS

A skin incision of 3-4 cm in the proximal direction was made at the forearm, and the median nerve was visualized between the pronator teres muscle and the flexor digitorum superficialis. Subsequently, the anterior interosseus nerve branch was identified, followed distally and decompressed under endoscopic view. The procedure could be accomplished in all cases under endoscopic view. Due to the very steep surgical angle, a branch of the anterior interosseus nerve was injured in one cadaver case. In all other cases, no adverse effects were observed. In the clinical case, the anterior interosseus nerve was endoscopically identified and decompressed, but a skin incision of 5 cm was required.

CONCLUSIONS

The results demonstrate that an endoscopic decompression of the anterior interosseus nerve is possible. Several difficulties occurred: Due to the depth of the surgical approach, especially in case of bulky muscles and very small skin incisions, the view is limited, harboring a higher risk of nerve injury. With more experience and specially designed endoscopes, application of this technique in anterior interosseus nerve compression syndrome might become more feasible.

Clinical and pathophysiological concepts of neuralgic amyotrophy

Neuralgic amyotrophy--also known as Parsonage-Turner syndrome or brachial plexus neuritis--is a distinct and painful peripheral neuropathy that causes episodes of multifocal paresis and sensory loss in a brachial plexus distribution with concomitant involvement of other PNS structures (such as the lumbosacral plexus or phrenic nerve) in a large number of patients. The phenotype can be limited or extensive and the amount of disability experienced also varies between patients, but many are left with residual disabilities that affect their ability to work and their everyday life. Both idiopathic and hereditary forms exist. The latter form is genetically heterogeneous, but in 55% of affected families, neuralgic amyotrophy is associated with a point mutation or duplication in the SEPT9 gene on chromosome 17q25. The disease is thought to result from an underlying genetic predisposition, a susceptibility to mechanical injury of the brachial plexus (possibly representing disturbance of the epineurial blood-nerve barrier), and an immune or autoimmune trigger for the attacks. The precise pathophysiological mechanisms are still unclear; treatment is empirical, and preventive measures are not yet available. This Review provides an overview of the current clinical and pathophysiological concepts and research topics in neuralgic amyotrophy.

Anatomic variation of the innervation of the flexor digitorum profundus muscle and its clinical implications

In anterior interosseous nerve syndrome and ulnar neuropathy, paralysis or weakness of the flexor digitorum profundus (FDP) muscles has been shown to vary according to the degree of involvement of the median and ulnar nerves, respectively. We traced these nerves in 50 cadaveric specimens in which each FDP was completely separated. The specimens were classified into six anatomic and another six presumptive electromyography (EMG) types according to the innervation patterns of the entire and the proximal one-third of the FDP muscles, respectively. The diverse anatomic and presumptive EMG types in this study suggest that the FDP muscles of the 2nd to the 5th digits should be examined by functional tests and EMG in lesions of the median or ulnar nerve.

Anterior interosseous nerve conduction study: normative data

Neurophysiological techniques assessing anterior interosseous nerve (AIN) function and employing surface electrode recordings from the flexor pollicis longus (FPL), have been limited by technical difficulties. The aim of this study was to describe a surface electrode recording technique of investigating the AIN by recording compound muscle action potentials (CMAPs) from FPL. CMAP responses exhibited a negative onset, suggesting that they originated from FPL, and this was confirmed by needle recording. Normative data has been established that may prove useful in future studies assessing pathological involvement of the anterior interosseous nerve.

Herpes zoster of the head and limbs: electroneuromyographic and clinical findings in 158 consecutive cases

OBJECTIVES

To quantify electromyographic and neurographic changes and to correlate them with the clinical data of outpatients with herpes zoster.

DESIGN

Prospective case series.

SETTING

Outpatient department.

PATIENTS

A consecutive, unselected series of 158 outpatient cases (88 women, 70 men; mean age, 64y) of herpes zoster of the head and limbs.

INTERVENTIONS

Not applicable.

MAIN OUTCOME MEASURES

Blink reflex and electromyography and motor and sensory nerve conduction velocities of nerves and muscles corresponding to affected dermatomes.

RESULTS

Postherpetic neuralgia (PHN), segmental zoster paresis, and polyneuropathy were found in 31%, 19%, and 2.5% of cases, respectively. Absence or reduction of sensory action potential amplitudes, blink reflex areas, and compound muscle action potential amplitudes were found in 60%, 31%, and 18% of cases, respectively. Sensory and motor conduction velocities and motor and blink reflex latencies were nearly always normal or only slightly slowed. Electromyographic signs of abnormal spontaneous activity were found in 36% of the cases. Electrophysiologic alterations were correlated among themselves, with age, with presence of segmental zoster paresis, and with absence of antiviral therapy. The extent of the skin rash (number of dermatomes affected by herpes zoster) was the only variable predictive of disappearance or improvement of PHN.

CONCLUSIONS

Sensory axonal neuropathy, often associated with similar motor involvement, can be shown by classical electrophysiologic methods in herpes zoster. The severity of damage to motor fibers was related to damage to sensory fibers, but no relation was found between peripheral axon damage and PHN. The site of motor system damage may be the ventral roots, plexus, or peripheral nerve. The probability of complications and the severity of sensory and motor peripheral axonal damage were increased in older patients. Appropriate antiviral therapy seems to reduce the incidence of segmental zoster paresis and the severity of damage to the peripheral fibers. A reduced extent of herpetic rash was the only factor to correlate with a good outcome of PHN.

Anterior interosseous nerve palsy after cardiopulmonary resuscitation in a resuscitator with undiagnosed muscle anomaly

IMPLICATIONS

We present a case of nerve palsy after cardiopulmonary resuscitation in a resuscitator with undiagnosed muscle anomaly. Effort-related nerve palsy may occur after prolonged performance of CPR.

Anterior interosseous nerve syndrome presenting with pronator teres weakness: a case report

Anterior interosseous nerve syndrome (AINS) has been well described. A key muscle to examine clinically and on electromyography is the pronator teres, as this can differentiate between forearm and more proximal entrapment sites. We present a case of AINS with marked weakness and denervation of pronator teres. At operation the anterior interosseous nerve gave rise to the nerve to pronator teres and was entrapped by a fibrous band from the deep head of pronator teres.

Electrodiagnostic testing in hand surgery

General techniques of electrodiagnostic examination, how such examination can predict the pathophysiology of nerve injury, and specific techniques and findings of the major entrapments such as carpal tunnel syndrome and ulnar nerve neuropathy are described in detail. Additional disease states that relate to hand surgery, such as anterior interosseous syndrome, brachial plexopathy, radiculopathy, polyneuropathy, and the nebulous entity of thoracic outlet syndrome are discussed.