Brachial plexus involvement in familial pressure-sensitive neuropathy: electrophysiological and morphological findings

Charcot-Marie-Tooth disease (hereditary motor sensory neuropathies) and hereditary sensory and autonomic neuropathies

BACKGROUND

Since the description of Charcot-Marie-Tooth disease over a century ago. it has now been recognized that these conditions are not caused by generalized metabolic defects but rather have various discrete genetic origins. These disorders can also have variable phenotypes due to dysfunction of peripheral nerve axons or their myelin due to the genetic defects that affect the formation of specific nerve proteins.

REVIEW SUMMARY

This article summarizes the clinical presentation of various phenotypes of the hereditary motor sensory neuropathies and the hereditary sensory and autonomic neuropathies, genetic mutations, and their relevant protein products. Proper identification of the genetic defects provides the opportunity for better genetic counseling and hopefully therapies in the future.

Phenotypic Variability Leads to Under-recognition of HNPP

OBJECTIVE

To determine the range of phenotypic expression in individuals with hereditary neuropathy with liability to pressure palsy (HNPP) with the chromosome 17 deletion.

METHODS

Twenty-one patients from 10 families were studied. Genetic testing was performed in at least one member of each family. Every patient was examined clinically, electrophysiological data was available in 18 patients, and a sural nerve biopsy was performed on 4 patients. In addition, a patient symptom questionnaire was administered over the telephone to identify symptomatic individuals from the at-risk population.

RESULTS

The identified phenotypes were those of compressive neuropathy, symmetric peripheral neuropathy (often misdiagnosed as Charcot-Marie-Tooth neuropathy), acute brachial paralysis, and confluent mononeuropathy multiplex. Many individuals were oligosymptomatic and these formed the majority of undiagnosed patients.

CONCLUSIONS

The presence of mild symptoms and the marked phenotypic variability of the disease result in underdiagnosis of HNPP.

Clinical spectrum of the tomaculous neuropathies. Report of 60 cases and review of the literature

Tomaculous neuropathy has a distinctive pathological pattern of myelin thickenings in a high proportion of internodes but no specific pattern of nerve degeneration. We have analyzed the variable clinical expression of this disorder in a large series of patients. Different phenotypes have been recognized: the majority of our patients (52 cases) had hereditary neuropathy with liability to pressure palsy (HNPP) showing wide variability of clinical progression and of severity of the single episodes. 3 patients suffered from familial recurrent brachial plexus neuropathy (FBPN); 5 patients had a symmetrical progressive sensorimotor involvement of the limbs (SSMN), predominantly in the distal portions and leading to permanent disability. The explanation for this clinical variability does not emerge from our data or from the literature. Segmental demyelination is the major change correlating with the episodes of nerve palsy; axonal degeneration might be rarely associated. The myelin sausages are the markers of a selective vulnerability of the nerve fibers either to mechanical injury or to some other unknown event.

Hereditary neuropathy with liability to pressure palsies: a clinical, electroneurophysiological and morphological study

Clinical, electroneurographic and myographic studies were performed on 99 patients of 13 families having hereditary neuropathy with liability to pressure palsies (HNPP) and on 116 relatives. Diagnosis was confirmed in all families by a nerve biopsy of the index case. Large focal myelin thickenings (tomacula) were found in nerve biopsies of affected persons, whether or not pressure palsies had occurred. By using three electroneurographical parameters it was possible to discriminate between asymptomatic patients and unaffected relatives. Complaints sometimes mentioned in literature as being associated with HNPP such as low back pain, brachialgia and short lasting paraesthesia are not related to HNPP. The hereditary transmission is autosomal dominant with total penetration but variable expression.

Clinical and electrodiagnostic findings, nerve biopsy and blood group markers in a family with hereditary neuropathy with liability to pressure palsies

Clinical, electrophysiologic and biopsy findings as well as studies of blood group markers in a family with hereditary neuropathy with liability to pressure palsies (HNPP) are reported. There was an autosomal dominant trait without genetic linkage between the HNPP gene and blood group markers controlled by chromosome 1. Reduced motor and sensory nerve conduction velocity was found in clinically affected and unaffected nerves. Characteristic morphological changes in sural nerve biopsy including tomaculous swelling were present.

Idiopathic brachial plexus lesion with conduction block of the ulnar nerve

A 24-year-old male with idiopathic acute aching of the right wrist, weakness of ulnar innervated muscles of the forearm and hand, and numbness of the ulnar two digits, was examined electrophysiologically. Conduction studies showed almost complete conduction block of motor fibers of the ulnar nerve distally in the brachial plexus. Sensory fibers were less affected. The symptoms and pathophysiological findings improved over a period of 1-2 months and were normal at the final study performed 7 months after presentation. There was mild evidence of chronic partial denervation of the abductor digiti V and the flexor digitorum profundus of the two ulnar digits. There were additional mild EMG changes of the abductor pollicis muscle indicating minor involvement of the median nerve. There was no traumatic or other obvious cause for these findings. It is suggested that the patient had a mild and abortive form of brachial plexus neuropathy presenting as a demyelinating lesion rather than the more typical wallerian degeneration seen in most established cases.

Recurrent familial neuropathy due to liability to pressure palsies

Two families with hereditary neuropathy with liability to pressure palsies (HNPP) were evaluated clinically, electrophysiologically and pathologically (2 index cases). Familial patterns suggest autosomal dominant inheritance. The clinical presentation is characteristic, with recurrent painless transitory mononeuropathy, without evident triggering factors, or caused by trivial trauma or pressure. In affected members neurophysiological studies showed diffuse slowing in nerve conduction, more evident at common sites of entrapment. Somatosensory evoked potentials (SEPs) showed bilateral peripheral abnormalities with proximal nerve involvement more pronounced in older patients. 40 to 75% of teased fibers displayed sausage-shaped swellings. Ultrastructurally some sausages showed redundant myelin loops and excessive number of myelin lamellae that seem to cause axonal constriction.

Hereditary recurrent brachial plexus neuropathy with dysmorphic features

A Finnish pedigree comprising 13 members in 3 generations with recurrent brachial plexus neuropathy is described. The disease was characterized by repeated attacks of pain in the upper limb/shoulder region, followed by muscle weakness and atrophy. The first episode usually occurred in childhood after a mild infection. Symptoms varied in intensity and seldom left marked neurological deficiencies. Patients had typical features including hypotelorism, small palpebral fissures and a small oral opening. The distribution of the affected members in the pedigree was compatible with autosomal dominant inheritance with high penetrance. Despite the limitation of the symptoms to the upper limbs, sural nerve biopsy showed tomaculous neuropathy in an affected member of the family. The structural changes of tomaculous neuropathy probably reflect a genetically determined generalized abnormality of the Schwann cells predisposing the patients to the recurrent palsies by exogenous factors.

Multiple exercise-related mononeuropathy with abdominal colic

Hereditary neuropathy with liability to pressure palsies (NLPP) is a rare disease characterized by recurrent sensory-motor deficits precipitated by exposure to minor pressure. This report describes a variant of this neuropathy in 5 siblings suffering from painful palsies after strenuous work with concurrent episodes of abdominal colic resembling that of acute intermittent porphyria. Electrophysiological studies of the index case showed the typical abnormalities of motor and sensory nerve conduction, including clinically non-affected nerves. Light and electron-microscopic examination showed the characteristic lesions of the NLPP with sausage-like swelling of the myelin sheaths. In addition, non-compacted, "loose" myelin lamellae were frequently observed in association with distended Schmidt-Lantermann incisures. Non-compacted myelin was a prominent finding in this type of demyelinating neuropathy. We suggest that an unknown metabolic factor may induce both demyelination of peripheral nerve fibers and functional disturbance in autonomic nerves leading to attacks of abdominal pain.

Hereditary neuropathy with liability to pressure palsies. Report of two families and review of the literature

Clinical, neurophysiological and pathological investigations were carried out in 11 affected members of 2 families with hereditary neuropathy with liability to pressure palsies (HNPP). The observations were related to findings in 261 cases of 47 families published in the literature. It was concluded that HNPP is a nosological entity characterized by the following diagnostic criteria: (1) an autosomal dominant inheritance; (2) the clinical presentation of a recurrent mononeuropathy simplex or multiplex, frequently related to an inadequate trauma to peripheral nerves; (3) a significant slowing of motor and sensory conduction velocity in clinically affected, but also in clinically unaffected nerves; (4) characteristic morphological findings in sural nerve biopsy featuring "tomaculous" swellings of myelin sheaths, transnodal myelination and segmental demyelination. The pathogenesis of HNPP is not clear. Hypothetical explanations of the pathogenesis of HNPP are discussed.

Visual and somatosensory evoked potentials and F-wave latency measurements in hereditary neuropathy with liability to pressure palsies

Pattern shift visual evoked potentials (VEPs), cervical and cortical somatosensory evoked responses (SEPs) and motor conduction velocities studied by F-wave latency measurements were investigated in two family members with hereditary neuropathy with liability to pressure palsies (HN-PP). In both cases in VEPs and SEP conduction times N13-N20 were normal. A bilateral pathological increase of latencies of early SEP components, N9-N13 transit times and F-wave latencies revealed a lesion in the proximal parts of the median nerves close to the spinal cord in the older patient. These abnormalities emphasize the close relationship of HN-PP with hereditary polyradiculopathy (Mayer 1975).

Peripheral and central conduction times in hereditary pressure-sensitive neuropathy

Seven members of a family with histologically proven hereditary pressure-sensitive neuropathy (HPSN) agreed to be examine clinically and electrophysiologically. A sural nerve biopsy specimen taken from the propositus who suffered from a partial brachial plexus palsy showed typical 'sausage-like' myelin sheath thickenings reflecting a failure of axon-adjusted myelination. Reduced motor and sensory conduction velocities involving several nerves were found in the four family members with clinical signs of HPSN. In addition, central conduction times in the auditory and somatosensory pathways were determined measuring the interwave latency I-V in brainstem auditory-evoked potentials and the interpeak latency N14-N20 in median nerve sensory-evoked potentials. Central conduction times in both afferent systems were within normal limits. The absolute delay of peak N14 and N20 in median and P40 in tibial nerve-evoked potentials was probably due to an impaired conduction in the peripheral branch of the bipolar ganglion cell. Whether the central axon branch in the dorsal columns was also involved could not be decided.