Hereditary neuralgic amyotrophy. Clinical, genetic, electrophysiological and histopathological studies

Neuralgic amyotrophy: an underrecognized entity

Neuralgic amyotrophy (NA) is markedly underdiagnosed in clinical practice, and its actual incidence rate is about 1 per 1000 per year. In the current article, we provide an overview of essential information about NA, including the etiology, clinical manifestations, diagnostic investigations, differential diagnosis, treatment, and prognosis. The causes of NA are multifactorial and include immunological, mechanical, or genetic factors. Typical clinical findings are a sudden onset of pain in the shoulder region, followed by patchy flaccid paralysis of muscles in the shoulder and/or arm. A diagnosis of NA is based on a patient’s clinical history and physical examination. Gadolinium-enhanced magnetic resonance imaging and high-resolution magnetic resonance neurography are useful for confirming the diagnosis and choosing the appropriate treatment. However, before a diagnosis of NA is confirmed, other disorders with similar symptoms, such as cervical radiculopathy or rotator cuff tear, need to be ruled out. The prognosis of NA depends on the degree of axonal damage. In conclusion, many patients with motor weakness and pain are encountered in clinical practice, and some of these patients will exhibit NA. It is important that clinicians understand the key features of this disorder to avoid misdiagnosis.

Neuralgic amyotrophy: An update on diagnosis, pathophysiology, and treatment

In this review we provide a current overview of the clinical features, pathophysiology, epidemiology, and diagnostic and therapeutic strategies in neuralgic amyotrophy (NA). The disorder has several phenotypic variations, with a classic form in 70% of the patients. It is not rare, with an incidence of 1 per 1,000 individuals, but it is still often missed. Recurrences are common, yet the proposed multifactorial etiology, which includes genetic, biomechanical, and immunologic factors, limits our capacity to predict or prevent them. NA is a clinical diagnosis, and ancillary studies serve to exclude infectious or malignant causes or to assess a differential diagnosis. If patients are seen early and are still in pain, a short trial of high-dose oral corticosteroids is advised, and adequate analgesia may require opioids and non-steroidal anti-inflammatory drugs. Persistent complaints are common, and a multidisciplinary rehabilitation approach focusing on scapular coordination, energy distribution strategies, and self-management is indicated.

Inherited focal, episodic neuropathies: hereditary neuropathy with liability to pressure palsies and hereditary neuralgic amyotrophy

Hereditary neuropathy with liability to pressure palsies (HNPP; also called tomaculous neuropathy) is an autosomal-dominant disorder that produces a painless episodic, recurrent, focal demyelinating neuropathy. HNPP generally develops during adolescence, and may cause attacks of numbness, muscular weakness, and atrophy. Peroneal palsies, carpal tunnel syndrome, and other entrapment neuropathies may be frequent manifestations of HNPP. Motor and sensory nerve conduction velocities may be reduced in clinically affected patients, as well as in asymptomatic gene carriers. The histopathological changes observed in peripheral nerves of HNPP patients include segmental demyelination and tomaculous or "sausage-like" formations. Mild overlap of clinical features with Charcot-Marie-Tooth (CMT) disease type 1 (CMT1) may lead patients with HNPP to be misdiagnosed as having CMT1. HNPP and CMT1 are both demyelinating neuropathies, however, their clinical, pathological, and electrophysiological features are quite distinct. HNPP is most frequently associated with a 1.4-Mb pair deletion on chromosome 17p12. A duplication of the identical region leads to CMT1A. Both HNPP and CMT1A result from a dosage effect of the PMP22 gene, which is contained within the deleted/duplicated region. This is reflected in reduced mRNA and protein levels in sural nerve biopsy samples from HNPP patients. Treatment for HNPP consists of preventative and symptom-easing measures. Hereditary neuralgic amyotrophy (HNA; also called familial brachial plexus neuropathy) is an autosomal-dominant disorder causing episodes of paralysis and muscle weakness initiated by severe pain. Individuals with HNA may suffer repeated episodes of intense pain, paralysis, and sensory disturbances in an affected limb. The onset of HNA is at birth or later in childhood with prognosis for recovery usually favorable; however, persons with HNA may have permanent residual neurological dysfunction following attack(s). Episodes are often triggered by infections, immunizations, the puerperium, and stress. Electrophysiological studies show normal or mildly prolonged motor nerve conduction velocities distal to the affected brachial plexus. Pathological studies have found axonal degeneration in nerves examined distal to the plexus abnormality. In some HNA pedigrees there are characteristic facial features, including hypotelorism. The prognosis for recovery of normal function of affected limbs in HNA is good, although recurrent episodes may cause residual deficits. HNA is genetically linked to chromosome 17q25, where mutations in the septin-9 (SEPT9) gene have been found.

Motor root conduction in neuralgic amyotrophy: evidence of proximal conduction block

OBJECTIVE

To determine the presence and role of proximal conduction block in neuralgic amyotrophy.

METHODS

Percutaneous electrical stimulation of cervical roots and brachial plexus was employed in eight patients with neuralgic amyotrophy. Root to Erb's point compound muscle action potential amplitude ratios for abductor digiti minimi, extensor digitorum communis, biceps, and deltoid muscles were compared with results obtained from 10 healthy controls.

RESULTS

Conduction block in the nerve to one muscle was found in three of eight patients (38%) suggesting focal proximal demyelination. Repeat studies showed axonal degeneration, resolution, and persistence of conduction block in these three patients respectively.

CONCLUSION

Focal conduction block plays a significant part in the pathogenesis of neuralgic amyotrophy, which is generally regarded as an axon loss process. Therapeutic intervention should be directed to patients with persistent conduction block, with the aim of eradicating the block and possibly minimising subsequent axon loss.

Hereditary neuralgic amyotrophy associated with a relapsing multifocal sensory neuropathy

A family with neuralgic amyotrophy (idiopathic brachial plexus neuropathy) associated with a multifocal sensory neuropathy is described. Four members over two generations were affected by neuralgic amyotrophy, inherited as an apparent autosomal dominant trait; two also had a multifocal relapsing sensory neuropathy with the clinical features of Wartenberg's migrant neuropathy.

Recurrent brachial plexus neuropathy and giant cell arteritis

A 73-year-old women presented with a recurrent form of sporadic brachial plexus neuropathy, the so-called Parsonage and Turner syndrome. This diagnosis is based on clinical and electromyographic findings. Interestingly a biopsy of the temporal artery demonstrated a giant cell arteritis. The clinical picture started 2 weeks after an upper respiratory tract illness. The possible viral etiology of giant cell arteritis is considered. We think an immunological rather than ischemic disturbance may have caused the recurrent brachial plexus neuropathy. This case report suggests that giant cell arteritis be considered in the investigation of the Parsonage and Turner syndrome.

Recurrent forms of sporadic brachial plexus neuropathy. A report of two cases

Two patients presenting a relapsing form of sporadic brachial plexus neuropathy, the so-called Parsonage Turner syndrome, are reported. The diagnosis is based on clinical and electromyographic features. Recurrent attacks, although infrequently encountered, have been well described in the past. Sporadic cases of this syndrome must be differentiated from the familial varieties of neuralgic amyotrophy in which, two main subgroups of patients are distinguished: those showing facial dysmorphic features and those with findings of a tomaculous neuropathy predisposing them to pressure palsies. Apart from the obvious difference as regards familial occurrence, the familial and non-familial varieties of neuralgic amyotrophy differ in a number of respects: associated congenital defects, early age of onset and high rate of recurrence in the former. Finally some possible pathogenetic mechanisms of the syndrome are briefly reviewed.