Neuralgic amyotrophy

Mark A Ferrante MD (

Dr. Ferrante of the University of Tennessee Health Science Center has no relevant financial relationships to disclose.

)
Francesc Graus MD PhD, editor. (Dr. Graus of the University of Barcelona has no relevant financial relationships to disclose.)
Originally released May 14, 1996; last updated June 4, 2019; expires June 4, 2022

This article includes discussion of neuralgic amyotrophy, brachial neuritis, acute brachial neuropathy, acute brachial plexitis, acute brachial radiculitis, acute scapulohumeral paralysis, acute shoulder neuritis, brachial plexus neuropathy, cryptogenic brachial neuropathy, inflammatory brachial plexus neuropathy, localized neuritis of shoulder girdle, long thoracic neuropathy, multiple neuritis of shoulder girdle, neuralgic amyotrophy, paralytic brachial neuritis, Parsonage-Turner syndrome, and serratus magnus palsy. The foregoing terms may include synonyms, similar disorders, variations in usage, and abbreviations.

Overview

This article reviews neuralgic amyotrophy, a disorder which, through over a century, has been referred to by a myriad of other terms, including the eponymous term, Parsonage-Turner syndrome. Except for neuralgic amyotrophy, which conveys the 2 quintessential clinical features of this disorder, and Parsonage-Turner syndrome, which does not convey misleading information, the other terms are best avoided. These undesirable terms are descriptive and were coined based on a single clinical feature (eg, the involved muscle) or antecedent event (eg, vaccinogenic), a presumed localization (eg, the brachial plexus), or a presumed pathology (eg, inflammation), all of which are either inaccurate or unproven.

Because it conveys the 2 most important clinical features, this article utilizes the term neuralgic amyotrophy, which was originally introduced by Parsonage and Turner.

Unfortunately, even now, neuralgic amyotrophy is a relatively unknown entity to many healthcare providers, including many surgeons and anesthesiologists. For this reason, the recognition of this disorder by the neuromuscular medicine provider serves 2 important roles in addition to disease recognition: (1) it serves to prevent the mistaken consideration that the clinical features are due to the associated medical or surgical procedure (when this is the antecedent event) and (2) it serves to prevent unnecessary diagnostic testing and unhelpful therapeutic interventions (eg, surgery) from being performed.

Neuralgic amyotrophy is a disorder of the peripheral nervous system. Its 2 quintessential features – as indicated by the term neuralgic amyotrophy – are severe pain and significant forequarter muscle wasting. Both of these features involve the forequarter region of the body (ie, the cranial, shoulder, upper extremity, and ipsilateral chest wall). In the majority of cases, a precipitating antecedent event (also referred to as a trigger) can be identified.

Because the phenotypic presentation of neuralgic amyotrophy is extremely variable, neuralgic amyotrophy was not initially recognized as a single entity. As a result, each of its individual presentations was considered to be a separate disorder and received a separate name, resulting in a large number of recognized medical diseases that were in fact a single entity. Eventually, a unifying clinical triad was identified – an antecedent event (trigger), the sudden onset of severe forequarter region pain, and severe weakness and wasting of forequarter muscles – at which point it was realized that all of these disorders represented phenotypic variations of a single syndrome.

Even the variations of neuralgic amyotrophy reported in the literature (ie, the classic versus non-classic forms), simply reflect the nervous system element within the forequarter region involved (eg, cranial nerve, root, plexus, or nerve). Neuralgic amyotrophy may involve a single focus (most commonly a single nerve) or multiple foci (most commonly multiple nerves).

Although the majority of the lesions associated with neuralgic amyotrophy have been traditionally localized to the brachial plexus, many investigators have speculated that, at least on some occasions, the lesions must have an extraplexal localization. It was reported, however, that the overwhelming majority of these lesions are actually extraplexal (Ferrante and Wilbourn 2017). This distribution is due to the motor axon predilection of this disorder (discussed below).

This discussion reviews the demographic, genetic, and clinical features of neuralgic amyotrophy, as well as its differential diagnostic considerations, workup, and treatment. Regarding the latter, the first step is the recognition of neuralgic amyotrophy so that unnecessary diagnostic testing and inappropriate interventions are avoided.

Key points

 

• Despite considerable variation in the clinical features associated with neuralgic amyotrophy, its 2 main clinical features – severe and sudden-onset forequarter region pain and forequarter muscle weakness and wasting – especially when encountered in the setting of an antecedent event, typically make the diagnosis straightforward.

 

• Although most neuralgic amyotrophy patients only experience a single event, multiple bouts (ie, recurrences) occur in some. In our series, recurrences occurred in 12% of patients. When recurrent bouts occur, they may involve the same limb or the contralateral limb, and they may involve the same nerves or have a different distribution of nerve involvement. The interval between the bouts is unpredictable and can range from days to weeks (eg, with sequential bilateral involvement) to decades. Although there is no way to predict a recurrence, when the antecedent event is childbirth, especially when the woman has had 2 bouts of neuralgic amyotrophy associated with childbirth, there is a good chance that subsequent childbirth will precipitate another bout of neuralgic amyotrophy.

 

• When both sides are involved, their involvement is sequential in the majority and simultaneous in the minority.

 

• Although the exact pathophysiology is unknown, available evidence suggests that an autoimmune pathogenesis, likely related to a genetic susceptibility, most commonly generates an axon loss lesion (focal or multifocal) that involves predominantly motor axons and that is most commonly triggered by an immune-activating antecedent event.

 

• The motor axon predilection dictates the distribution and incidence of the lesions associated with neuralgic amyotrophy. Thus, pure motor nerves (including motor nerve branches to individual muscles) and predominantly motor nerves (nerves composed of predominantly motor axons with a much lesser number of cutaneous sensory axons) are much more frequently involved than are mixed nerves (ie, those containing a more balanced number of motor and cutaneous sensory axons) and cutaneous sensory nerves (nerves composed solely of cutaneous sensory nerves) (Ferrante and Wilbourn 2017).

 

• During the time when lesions associated with neuralgic amyotrophy were believed to represent brachial plexus involvement, 2 clinical features could not easily be explained: muscle sparing and quick recovery. Muscle sparing occurs when a single muscle shows severe weakness and wasting yet other muscles innervated by the involved nerve element are spared (eg, infraspinatus muscle involvement with supraspinatus muscle sparing) or when a single muscle head is severely involved and the others are spared (eg, isolated involvement of the lateral head of the triceps muscle with sparing of the other 2 heads). Because the lesions were assumed to be localized within the brachial plexus, whenever severely affected muscles showed rapid recovery, confusion ensued because such an occurrence could only be accounted for by a short reinnervation distance. When one accepts the idea that the focus often involves a distal motor nerve branch to an individual muscle, both of these phenomena are readily explained.

 

• Management of neuralgic amyotrophy consists of pain control and physical therapy. Although neuropathic pain medications are the mainstay, these medications take time to take effect. Thus, during the initial phase of the disorder when the pain is quite severe, opiates and corticosteroids are usually required.

 

• A familial form of neuralgic amyotrophy, referred to as hereditary neuralgic amyotrophy, accounts for a minority of neuralgic amyotrophy cases. In comparison to sporadic neuralgic amyotrophy, hereditary neuralgic amyotrophy has an earlier age of onset (it often begins in childhood), has more frequent recurrences, and may be associated with certain dysmorphic features (eg, hypotelorism, high-arched palate, syndactyly) (Dreschfeld 1886). The most common mutation associated with the hereditary form of neuralgic amyotrophy involves the septin-9 (SEPT9) gene on chromosome 17q25, but this disorder is genetically heterogeneous (Watts et al 2001; Kuhlenbaumer et al 2005). The gene is passed in an autosomal dominant manner and, thus, unlike sporadic neuralgic amyotrophy, which involves males to a greater extent than females, hereditary neuralgic amyotrophy involves males and females more equally.

 

• In addition to caring for the neuralgic amyotrophy patient, another critical role of the healthcare provider is to make the correct diagnosis, thereby avoiding subjecting the patient to unnecessary testing and unhelpful surgical procedures.

Historical note and terminology

Historically, 2 separate disorders, serratus magnus paralysis and postinfectious paralysis were described in the mid-1800s. As discussed above, serratus magnus paralysis reflected the muscle involved (the serratus magnus muscle, currently termed the serratus anterior muscle) and postinfectious paralysis indicated that the disorder followed an infection. Later that century, 2 other entities, serogenic neuropathy and vaccinogenic neuropathy, were reported. The terms applied to these 2 disorders reflected their presumed precipitation – serum administration and vaccine administration, respectively. A number of other entities were subsequently identified and labeled using terms appropriate to their presumed location, pathology, or trigger. In 1948, Parsonage and Turner recognized the unifying characteristics of these disorders, leading to their conclusion that all of these disorders represented a single entity with a variety of presentations (Parsonage and Turner 1948). In addition, they also coined the term neuralgic amyotrophy based on their recognition of the 2 most quintessential clinical features – severe pain and significant muscle wasting. Following their report, the nondescriptive term Parsonage-Turner syndrome was added to the list of monikers. Of all of the terms, as stated above, neuralgic amyotrophy and Parsonage-Turner syndrome are preferred because they do not suggest a specific lesion location, a specific trigger, or a specific pathology. Because neuralgic amyotrophy conveys its 2 most important clinical features, it is the favored term in the current medical literature.

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