Dystrophia myotonica. Peripheral nerve involvement and pathogenetic implications

An Electrophysiological Method for Examining Lumbosacral Root Compression

The propagation velocities and conduction times of nerve impulses responsible for muscle F-waves were measured in the proximal segments of 60 normal posterior tibial nerves and of 41 normal peroneal nerves. The results were compared with those of 25 patients having confirmed lumbosacral root compression due to disc degeneration. Using the peroneal nerve, 65 per cent of patients had a prolonged proximal conduction time; a similar abnormality was found in 56 per cent of patients when the posterior tibial nerve was studied. The yield of positive results rose to 85 per cent and 76 per cent respectively when the M- and F-latencies in given individuals were compared. It was also shown that in normal subjects the F-response has a longer latency, and slower conduction velocity than the H-reflex when both are obtained using the same stimulating and recording sites, in patients in whom the ankle jerks and H-reflexes are absent, the F-waves may still be recorded, indicating that the latter are mediated through motor fibers

Toward a more personalized motor function rehabilitation in Myotonic dystrophy type 1: The role of neuroplasticity

Myotonic dystrophy type 1 (DM1) is the most prevalent adult muscular dystrophy, often accompanied by impairments in attention, memory, visuospatial and executive functions. Given that DM1 is a multi-system disorder, it requires a multi-disciplinary approach, including effective rehabilitation programs, focusing on the central nervous system neuroplasticity, in order to develop patient-tailored rehabilitative procedures for motor function recovery. Herein, we performed a transcranial magnetic stimulation (TMS) study aimed at investigating central motor conduction time, sensory-motor plasticity, and cortical excitability in 7 genetically defined DM1 patients. As compared to healthy individuals, DM1 patients showed a delayed central motor conduction time and an abnormal sensory-motor plasticity, with no alteration of cortical excitability. These findings may be useful to define patient-tailored motor rehabilitative programs.

Peripheral neuropathy in myotonic dystrophy type 1

Myotonic dystrophy 1 (DM1) is characterized by a wide range of clinical features. We aimed to verify the presence of peripheral nerve involvement in a large cohort of DM1 patients and to determine clinical consequences. A total of 93 patients underwent detailed neurological examination and nerve conduction studies. Additionally, balance impairment was assessed with the Berg Balance Scale and health status was evaluated with the SF-36 health survey. Sensory symptoms were not reported and mild sensory signs were found in six patients. Electrophysiological abnormalities consistent with a diagnosis of neuropathy were found in 16 patients (17%). Peripheral nerve involvement was significantly associated with decreased muscle strength (p = 0.001) and absence of Achilles-tendon reflexes (p = 0.003), but not with age or duration of neuromuscular symptoms. It had no significant effect on balance, mental or physical health. In conclusion, peripheral nerve involvement may be one of the multisystemic manifestations of DM1, but is usually subclinical. Other causes should be excluded when sensory symptoms or signs are severe.

Myotonic dystrophy presenting as new-onset hand weakness and recurrent pneumonia in a patient with paraplegia: A case reportaaNo commercial party having a direct financial interest in the results of the research supporting this article has or will confer a benefit upon the authors(s) or upon any organization with which the author(s) is/are associated

We describe a previously independent T11 paraplegic patient who had delayed-onset hand weakness and recurrent pneumonia caused by myotonic dystrophy. A man in his late thirties suffered a thoracic spinal cord injury (SCI) from a gunshot wound at the age of 17 years, with resultant T11 American Spinal Injury Association class A paraplegia. He lived independently until the age of 36 years when he was hospitalized multiple times for pneumonia. During a rehabilitation stay after one of the acute hospitalizations, the patient's hand weakness and diffuse muscular atrophy were noted. Electrodiagnostic testing was performed, which showed myotonic discharges. Genetic testing was consistent with myotonic dystrophy. This case shows the importance of considering causes of weakness that affect the population as a whole when evaluating a patient with SCI who presents with delayed-onset weakness.

Radial nerve F-waves: normative values with surface recording from the extensor indicis muscle

OBJECTIVES

In the present study we set out to obtain normative values for radial nerve F-waves, with surface recording from the extensor indicis muscle.

METHODS

Forty-nine patients with unrelated complaints were tested. Surface recording electrodes were placed on the extensor indicis muscle. This was found by asking the patient to extend the second digit against resistance. The active surface recording electrode was placed over the most distal portion of the muscle, near the radial border of the ulnar bone near the wrist. Stimulation was performed near the lateral epicondyle between the radial and ulnar bones.

RESULTS

The mean F-wave minimum latency was found to be 20.55 ms, with an upper limit of 24.35 ms. The absolute interside minimum latency difference was found to have a mean of 0.55 ms, with a maximum of 1.7 ms. The mean amplitude of the F-waves was 145.61 microV and the mean mF/M ratio was 0.022. F-waves were unobtainable in 2/62 (3.2%) of limbs. Normative values for the radial nerve motor response were also obtained. Three cases are described to illustrate the usefulness of the above technique.

CONCLUSIONS

It is technically feasible to record radial nerve F-waves from the extensor indicis muscle.

Neurophysiological and radiological findings in myotonic dystrophy patients

Somatosensory evoked potentials (SEPs) and brainstem auditory evoked potentials (BAEPs) were recorded in 10 patients with myotonic dystrophy and in 20 sex and age-matched healthy controls. In all patients a brain MRI examination was also performed. In our results, the significantly longer absolute peak latencies of the SEPs and the abnormal increasing of the later components of the BAEPs suggest an involvement of the afferent sensory and central auditory pathways. Brain MRI showed white matter hyperintense lesions (WMHL) in eight patients (80%). No correlations were found between individual abnormal electrophysiological parameters or severity of WMHL and age, age at onset, disease duration or muscular impairment. The total number (SEP + BAEP) of electrophysiological abnormalities significantly correlated with muscular impairment (p < 0.05) and MRI changes (p < 0.005), suggesting a strict pathogenetic linkage between muscular and nervous system alterations in this disease.

Magnetic stimulation study in patients with myotonic dystrophy

To further define motor nervous system alterations in myotonic dystrophy (MD), motor potentials to transcranial and cervical magnetic stimulation (MEPs) were recorded from the right abductor pollicis brevis muscle in 10 patients with MD and in 10 healthy controls. Cortical and cervical latencies, central motor conduction time (CMCT), stimulus threshold intensity and cortical MEP amplitudes expressed both as absolute values and as %M were analysed. MEP cervical latency, absolute or relative amplitude and excitability threshold did not significantly differ in patients and controls. The mean cortical motor latency and CMCT were significantly prolonged in MD patients with respect to normal subjects. Moreover, CMCTs were found to be significantly related to stimulus threshold intensity (P = 0.03) and only marginally related to absolute cortical amplitude (P = 0.06). These findings are indicative of a central motor delay, also related to decreased excitability of motor neurons, in patients with MD. No correlations were found between individual neurophysiological parameters and age, duration of disease and clinical impairment. Our results suggest that magnetic stimulation studies can detect subclinical dysfunctions of the central motor system in MD patients, as one of the multisystemic manifestations of the disease, rather independent of the primitive muscle damage.

Motor unit estimation: anxieties and achievements

The history of motor unit number estimation (MUNE) is given, together with brief descriptions of the various methods presently available. A small muscle of the hand contains about 100 motor units and greater numbers are found in larger muscles; beyond 60 years the numbers begin to decline. In ALS approximately half the motor units cease to function within 6 months of the involvement of the motoneuron pool, while in adult spinal muscular atrophy further loss may not occur over several years. The reduction in MUNE values in myotonic dystrophy remains an enigma, but even more curious are the losses and subsequent recoveries occasionally observed in hyperthyroidism and chronic renal failure; possibly, nontransmitting ("silent") synapses are involved. MUNE may also be used to study CNS problems such as hemiplegia and congenital brachial palsy. The availability of more powerful computers for EMG should lead to advances in MUNE.

Muscle histopathology in myotonic dystrophy in relation to age and muscular weakness

We studied histopathological changes in the biceps brachii muscle in relation to age and the degree of muscle weakness in 64 patients (aged 11-59 years) with myotonic dystrophy. The proportion of type 1 fibers was unaltered in the adolescent patients compared with control values, but increased with age. The average diameters of all the fiber types were smaller than control values in the adolescents, suggesting immature development; however, there was an increase in diameter with age that was associated with an increase of hypertrophic type 2 fibers. At all ages, type 1 fibers were smaller than type 2 ones. Small angular fibers and small group atrophy consisted mainly of type 1 fibers, their incidences decreasing with age. The severity of muscular weakness was related to the predominance of type 1 fibers, the reduction in the number of hypertrophic type 2 fibers, and the accumulation of adipose cells, but not to the presence of small angular fibers or to small group atrophy.

Axonal motor and sensory neuropathy in myotonic dystrophy

We report the neurophysiological findings from 24 subjects with myotonic dystrophy of Steinert and the histological findings in two of them. The conduction data is compared with that of a group of subjects with Landouzy-Déjérine muscular dystrophy. In 46% of cases, the electrophysiological data revealed slight and generalized axonal neuropathy. Histological results of sural nerve confirmed axonal damage of sensory fibres. The neuropathy was not correlated with age of patients, duration or onset of the disease, nor with the state of the deep reflexes; it did not show signs of progressing and is probably one of the multisystemic manifestations of gene pleiotropism.

Myotonic dystrophy and traumatic quadriplegia: case report

A thirty-year-old man with traumatic quadriplegia, was also found to have weakness above the level of the injury. He had facial weakness, difficulty in swallowing, and recurrent respiratory problems. A diagnosis of myotonic dystrophy was supported by examination of his sister. The problems of diagnosis, and the implications of the diagnosis on the management of the patient with myotonic dystrophy and a spinal injury are discussed.

Invited review: motor unit estimation: methods, results, and present status

The renewed interest in motor unit estimation (counting) has coincided with the introduction of computer-based methodology and with the application of the technique to proximal as well as distal muscles. The advantages and disadvantages of the different methods are considered, together with the assumptions inherent in this type of examination. In normal subjects, the extensor digitorum brevis (EDB) muscle has approximately 200 motor units while each of the intrinsic muscles of the hand has about 100 units; larger muscles in the limbs contain greater numbers of units. Beyond the age of 60 years, there is a decline in the number of functioning motor units in both proximal and distal muscles. In denervating disorders, motor unit estimation is useful for diagnosis and assessment; abnormal values may often be observed in muscles judged clinically to be unaffected. Serial studies have enabled the rate of motor unit loss to be determined in ALS and in spinal muscular atrophy. Depletion of motor units has also been found following upper motoneuron lesions caused by injury to the spinal cord or by cerebral hemorrhage; trans-synaptic dysfunction has been presumed responsible. Rather surprisingly, reduced numbers of motor units have been observed in a variety of myopathic disorders; of these, the most consistent abnormalities have been reported in myotonic muscular dystrophy.

The anal sphincter in patients with myotonic muscular dystrophy

The objective of this prospective study was to determine anal sphincter function and thickness of the anal musculature in patients with myotonic muscular dystrophy. Manometric studies were performed in 16 patients with myotonic dystrophy and in 16 healthy controls. Patients had significantly lower basal and squeeze pressures than control subjects (P less than 0.01). The results of ultrasonographic studies of the anal canal in 7 patients and 7 control subjects suggest that this decrease in muscle strength is partly explained by muscular atrophy. In addition, patients with myotonic dystrophy showed exaggerated rebound contractions following and sphincter relaxation that was induced by rectal distention. The pattern of this response and the results of electromyographic studies in 6 patients with myotonic dystrophy suggest that such abnormalities are explained by a neurogenic defect rather than a myotonic response of the anal musculature. It is concluded that patients with myotonic dystrophy show a multitude of defects in the anal sphincter that are an expression of myopathy, muscular atrophy, and neural abnormalities.

Skeletal muscle changes associated with equine myotonic dystrophy

A progressive neuromuscular disorder in young horses, clinically apparent as early as 1 month of age, is characterized by generalized myotonia, muscle stiffness, muscle weakness and atrophy. Myotonia is identified by percussion dimpling and myotonic EMG discharges. Changes in one case included testicular hypoplasia, cataract formation, and glucose intolerance, indicating a systemic involvement. Pathologic changes in skeletal muscles from three affected foals were examined. Sarcoplasmic masses, ringed fibers, internal positioning of sarcolemmal nuclei, and nuclear rowing were among the primary histologic changes noted. Variation in fiber diameter size, especially atrophy, and type I predominance were also prominent changes. A neurogenic involvement was indicated by type grouping changes in several muscles.

Multimodal evoked potentials, EEG and electroretinography in patients with dystrophia myotonica

EEG, somatosensory (SEP) and visual evoked potentials (VEP) and electroretinography (ERG) were recorded from 16 patients with clinical and electromyographically verified dystrophia myotonica. The results were compared to an age- and sex- matched control group and revealed statistically significant differences between the group mean values for almost all records. Furthermore, abnormal individual electrophysiological tests were relatively frequent in the patient group. No correlation was found between abnormalities in one test compared to abnormalities in the other tests. Furthermore, no correlation was found between the number of electrophysiological abnormalities and the frequency of the disease in the nearest family. The number of abnormal electrophysiological tests increased, however, with age of the patients and duration of the disease.

Peripheral neuropathy in myotonic dystrophy: a nerve biopsy study

Sural nerve biopsies from 13 unselected myotonic dystrophy patients and 6 normal controls were studied morphometrically. The myelinated fiber density was reduced in 11 of the 13 myotonic dystrophy patients, with preferential loss of large myelinated fibers. Unmyelinated fiber densities and diameters were normal. Teased fiber studies commonly revealed focal areas of remyelination and abnormal wrinkling of the myelin sheath. Measurement of internodal length disclosed features of both axonal regeneration and focal demyelination-remyelination. These findings are consistent with a chronic axonopathy of moderate severity, possibly due to axonal atrophy.

Motor endplate involvement in the extraocular muscles of the myotonic rat

The motor endplates from the extraocular muscles of rats administered 20,25-diazacholesterol were examined by electron microscopy. Many anomalies were found at various levels of the junctional complex. Electron microscopy showed disrupted sole-plate nuclei, disruptions of the junctional sarcoplasm, atypical sarcoplasmic extensions, simplified postsynaptic areas, and interposition of Schwann cell cytoplasm between axonal terminal and muscle fiber with a reduplication of basement membrane, as well as atrophic and disrupted axonal terminals. These data indicate that the motor endplate is affected as well as the muscle fiber in myotonic dystrophy.

Dantrolene sodium and dystrophia myotonica

A patient with dystrophia myotonica was given dantrolene sodium to try to provide muscle relaxation during a cholecystectomy. Dantrolene was used as it is accepted that the drug has a place in the control of spasticity and also causes muscle relaxation, whereas conventional muscle relaxants are unable to control myotonia of muscle origin. Dantrolene alone did not provide good enough intubating and operating conditions in this subject. Later studies showed that, after dantrolene, EMG recordings from the patient were not significantly altered, although an impression of a slight increase in the myotonic potentials was gained.

Short-latency somatosensory evoked potentials in dystrophia myotonica

Somatosensory evoked potentials (SEPs) were recorded in a group of 21 patients with dystrophia myotonica and in a group of controls. Those with dystrophia myotonica had longer absolute peak latencies due to slower peripheral conduction. SEP abnormalities revealed peripheral and/or central conduction delays in 33% of the dystrophia myotonica subjects. There was no apparent relationship between the clinical severity of the disease and SEP abnormality.

Autosomal recessive generalized myotonia

Two siblings and a first degree cousin of a consanguinous marriage were afflicted with recessive generalized myotonia (RGMy). All had muscle weakness which was particularly prominent after rest, thinning of the forearms, weakness of anterior compartment muscles, and muscular contractures. The first degree cousin was the most severely afflicted with congenital myotonia. Muscle biopsy and electromyography were consistent with a myopathy. Exercise after rest demonstrated a marked reduction in muscle membrane excitability in all patients.

Axonal transport dysfunction in dystrophia myotonica

Axonal transport of acetylcholinesterase (AChE) was measured in the median and sural nerves of a subject who suffered from dystrophia myotonica and in a control subject. It was found that the basal activity of AChE was increased in myotonic nerves while its proximodistal transport was inhibited.

Incidence, severity, and time-course of motoneurone dysfunction in myotonic dystrophy: their significance for an understanding of anticipation

The numbers of functioning motor units and the amplitudes of the maximum evoked muscle responses have been measured in 198 muscles of 102 patients with myotonic dystrophy. Losses of units could be demonstrated in most of the extensor digitorum brevis and thenar muscles but less commonly in the hypothenar groups. A more proximal limb muscle, the soleus, was also shown to be involved frequently. Investigation of two premature infants withmyotonic dystrophy also revealed reductions of functiong units; in one infant clinical improvement was associated with increased muscle innervation. Repeated examinations of 10 adult patients disclosed an abnormal decline in neuromuscular function below the age of 60 years. The reduction in functioning units amounted to approximately 3% of the mean control value per annum. Analysis of 19 families showed that the severity of neuromuscular involvement was nearly always greater in members of later generations. If the predicted deterioration was also taken into account, the results strongly suggested that anticipation was a true genetic phenomenon rather than an artefact of selection. The combined results are considered to strengthen the concept of motoneurone dysfunction as the major pathogenetic factor in this form of dystrophy.

F-wave conduction velocity in the deep peroneal nerve: Charcot-Marie-Tooth disease and dystrophia myotonica

The F-wave has been used to estimate the motor nerve conduction velocity (MNCV) along the proximal segment (spinal cord to knee) of the axons of the deep peroneal nerve in patients with Charcot-Marie-Tooth disease and those with dystrophia myotonica. A new, modified method has been applied to estimate proximal MNCV in patients in whom F-waves or M-responses cannot be obtained from the small muscles of the foot. Terminal latencies and MNCV along the distal nerve segment (knee to ankle) have also been estimated using conventional techniques. The results have been compared with those obtained for control subjects. Proximal MNCV was severely slowed in every patient with Charcot-Marie-Tooth disease; the degrees of proximal and distal MNCV decreases were related. In patients with dystrophia myotonica, distal and proximal MNCVs were significantly reduced in comparison with control subjects, the MNCV slowing was not related to the degree of muscle atrophy. This is consistent with the hypothesis that the nerves and muscles are independently affected in dystrophia myotonica. It is concluded that the F-wave MNCV technique is as useful as, and may be more sensitive than, the conventional MNCV method.

The development of the extensor digitorium brevis muscle in progressive proximal muscular antrophies

The development of the extensor digitorium brevis (EDB) muscle was studied in 39 healthy subjects, 27 patients with progressive proximal spinal muscular atrophy, 20 patients with limb-girdle muscular dystrophy and three with facioscapulohumeral muscular dystrophy. The EDB muscle is spared and usually hypertrophic in patients with muscular dystrophy, whereas it is often atrophic and weak in patients with spinal muscular atrophy. It is proposed that the degree of development of the EDB muscle can be used as a clinical sign in the differential diagnosis of progressive muscular atrophies.

Myotonic dystrophy with nerve hypertrophy. Report of a case with electrophysiological and ultrastructural study of the sural nerve

A striking enlargement of peripheral nerves was observed in a patient with myotonic dystrophy (Steinert's disease). Clinical findings disclosed a polyneuropathy which was confirmed by electrophysiological and morphological investigations. Myopathic as well as neurogenic alterations were found on electromyography in wasted hand muscles. The prominent finding on ultrastructural study of sural nerve biopsy was an important collagen infiltration with rather few "onior bulb" formations. This extensive endoneural collagen formation appeared to be responsible for the nerve hypertrophy. Evidence of segmental demyelination and remyelination was also found. Glycogen deposits were present in some myelinated axons and is some Schwann cells. Peculiar crystalline inclusions were observed in fibroblasts processes. The relation between myotonic dystrophy and polyneuropathy remains a matter of discussion.

F-wave studies on the deep peroneal nerve. Part 1. Control subjects

An electrophysiological method is described for estimating the conduction velocity in the proximal segments (anterior horn cells to the knee) of the motor fibres of the deep peroneal nerve. The method utilizes large numbers of F-waves which are late muscle responses due to antidromically activated motoneurones. The results in 58 healthy subjects are presented. A detailed literature review concerning the nature of F-wave is presented.

Dystrophia myotonica. A model of combined neural and myopathic muscle atrophy

Reports on clinical, electrophysiological and histological studies in dystrophia myotonica have shown that the peripheral nerves are usually not intact. In a few patients the neuropathy exceeds the myopathy. On the basis of these findings some authors believe that muscle changes in dystrophia myotonica are entirely due to the nerve lesions. However, despite the commonly found evidence of neuropathy, electromyographic and muscle biopsy findings are reported usually as "myopathic". Furthermore, clinical and laboratory findings indicate that the degree of muscle atrophy and peripheral nerve changes are unrelated. This report attempts to explain the discrepancies by suggesting that the "myopathic" and "neuropathic" changes in the muscle fibres in dystrophia myotonica are independent processes.

The lack of deep reflexes in myotonic dystrophy

Clinical and electrophysiological observations have been carried out on 12 patients with myotonic dystrophy. Neurological examination showed that the tendon reflexes were absent or weak in almost all cases, whereas the cutaneous reflexes were normal. Examination of both deep and superficial sensibility gave normal results. Electromyography confirmed widespread "myopathic" activity and myotonic discharges were recorded on insertion of the needle electrode and at rest. Motor and sensory conduction velocity in the ulnar nerve and motor conduction in the peroneal nerve proved to be normal. Repetitive supramaximal nerve stimulation showed in 10 cases a decrease in potential amplitude, more evident at higher frequencies of stimulation. In the 2 other cases, by contrast, an increase in amplitude was observed, and this was suggestive of a partial presynaptic block. The jaw reflex was absent in 5 cases and reduced in amplitude in the 7 other cases. The results of blink reflex investigations were normal, with the exception of 2 cases where no early response was elicited. Spinal monosynaptic reflexes were absent in 7 cases after both electrical (H reflex) and mechanical stimulation (T reflex), whereas the response to direct stimulation of nerve motor fibres (the M response) was always present, even though reduced in amplitude. Such data lead one to reject the hypothesis that the absence of deep reflexes is due to pathological change in the muscle spindles. It seems more likely that the selective atrophy of Type 1 muscle fibres, known to be involved in deep reflex responses, is responsible for the early disappearance of the tendon reflexes.