Abnormalities of nerve conduction studies in myotonic dystrophy type 1: Primary involvement of nerves or incidental coexistence?

Characterization of the neuropathic pain component contributing to myalgia in patients with myotonic dystrophy type 1 and 2

Introduction

Chronic muscle pain is common in myotonic dystrophies (DM). Little is known about its pathophysiology. We aimed to investigate the characteristics of the neuropathic pain component contributing contributes to the pathogenesis of chronic pain in DM.

Methods

Twenty-one DM1 and 32 DM2 patients completed pain questionnaires (Brief pain inventory-BPI, PAIN-DETECT, pain disability index-PDI) and underwent neurological examination, nerve conduction studies (NCS), quantitative sensory testing (QST, dorsum of the right hand and right thigh) and skin biopsy to determine the intraepidermal nerve fiber density (IENFD, distal and proximal site of lower extremity). NCS and QST results at the thigh were compared to 27 healthy controls and IENFD and QST at the dorsum of the hand to published reference values.

Results

The sensory profile of DM2 patients was characterized by a loss in thermal and mechanical detection, while DM1 patients showed reduced mechanical and heat pain thresholds and higher mechanical pain sensitivity. Both DM groups showed pressure hyperalgesia. IENFD was reduced in 63% of DM1 patients and 50% of DM2. The slightly higher pain interference and disability found in DM2 was rather due to age difference than disease.

Conclusion

Similar pain mechanisms likely occur in both DM1 and DM2, even though a tendency toward more pain sensitivity was observed in DM1 and more sensory loss in DM2. Both QST and reduced IENFD highlight the presence of peripheral nerve damage in DM. This must be considered for the best pain management strategies.

Studying serum neurofilament light chain levels as a potential new biomarker for small fiber neuropathy

BACKGROUND AND PURPOSE

Diagnosing small fiber neuropathies can be challenging. To address this issue, whether serum neurofilament light chain (sNfL) could serve as a potential biomarker of damage to epidermal Aδ- and C-fibers was tested.

METHODS

Serum NfL levels were assessed in 30 patients diagnosed with small fiber neuropathy and were compared to a control group of 19 healthy individuals. Electrophysiological studies, quantitative sensory testing and quantification of intraepidermal nerve fiber density after skin biopsy were performed in both the proximal and distal leg.

RESULTS

Serum NfL levels were not increased in patients with small fiber neuropathy compared to healthy controls (9.1 ± 3.9 and 9.4 ± 3.8, p = 0.83) and did not correlate with intraepidermal nerve fiber density at the lateral calf or lateral thigh or with other parameters of small fiber impairment.

CONCLUSION

Serum NfL levels cannot serve as a biomarker for small fiber damage.

On the differential diagnosis of neuropathy in neurogenetic disorders

Neuropathy might be the presenting or accompanying sign in many neurogenetic and metabolic disorders apart from the classical-peripheral neuropathies or motor-neuron diseases. This causes a diagnostic challenge which is of particular relevance since a number of the underlying diseases could be treated. Thus, we attempt to give a clinical overview on the most common genetic diseases with clinically manifesting neuropathy.

Myotonic dystrophy type 1 alters muscle twitch properties, spinal reflexes, and perturbation-induced trans-cortical reflexes

BACKGROUND

Neurophysiologic biomarkers are needed for clinical trials of therapies for myotonic dystrophy (DM1). We characterized muscle properties, spinal reflexes (H-reflexes), and trans-cortical long-latency reflexes (LLRs) in a cohort with mild/moderate DM1.

METHODS

Twenty-four people with DM1 and 25 matched controls underwent assessment of tibial nerve H-reflexes and soleus muscle twitch properties. Quadriceps LLRs were elicited by delivering an unexpected perturbation during a single-limb squat (SLS) visuomotor tracking task.

RESULTS

DM1 was associated with decreased H-reflex depression. The efficacy of doublet stimulation was enhanced, yielding an elevated double-single twitch ratio. DM1 participants demonstrated greater error during the SLS task. DM1 individuals with the least-robust LLR responses showed the greatest loss of spinal H-reflex depression.

CONCLUSIONS

DM1 is associated with abnormalities of muscle twitch properties. Co-occurring alterations of spinal and trans-cortical reflex properties underscore the central nervous system manifestations of this disorder and may assist in gauging efficacy during clinical trials.

Assessment of small sensory fiber function in myotonic dystrophy type 1

BACKGROUND

Myotonic dystrophy type 1 (DM1) is a multisystem disorder affecting the peripheral nervous system. However, studies evaluating somatic small fiber sensory nerve function, which may contribute to pain in DM1, are lacking.

METHODS

Using quantitative sensory testing of the hand and foot, we evaluated Aδ and C-fiber function. Of 20 adult DM1 patients recruited, 16 were analyzed. Their results were compared with those of 32 age- and sex-matched controls.

RESULTS

No DM1 patient had diabetes mellitus or clinical evidence of small fiber neuropathy. In DM1, hand (P < .01) and foot (P = 0.02) warm detection thresholds were higher than those of controls. Cool detection thresholds were lower in the foot (P < .001).

CONCLUSIONS

Subclinical small sensory fiber dysfunction occurs in DM1 patients without large fiber neuropathy. Further research with other modalities is required to characterize these disturbances as disease modifying therapies are developed.

Core Clinical Phenotypes in Myotonic Dystrophies

Myotonic dystrophy type 1 (DM1) and type 2 (DM2) represent the most frequent multisystemic muscular dystrophies in adulthood. They are progressive, autosomal dominant diseases caused by an abnormal expansion of an unstable nucleotide repeat located in the non-coding region of their respective genes DMPK for DM1 and CNBP in DM2. Clinically, these multisystemic disorders are characterized by a high variability of muscular and extramuscular symptoms, often causing a delay in diagnosis. For both subtypes, many symptoms overlap, but some differences allow their clinical distinction. This article highlights the clinical core features of myotonic dystrophies, thus facilitating their early recognition and diagnosis. Particular attention will be given to signs and symptoms of muscular involvement, to issues related to respiratory impairment, and to the multiorgan involvement. This article is part of a Special Issue entitled “Beyond Borders: Myotonic Dystrophies—A European Perception.”

Neuromuscular transmission abnormalities in myotonic dystrophy type 1: A neurophysiological study

OBJECTIVES

Weakness and fatigue are frequent symptoms in myotonic dystrophy type 1 (DM1), mainly as a result of muscle impairment. However, neuromuscular junction (NMJ) abnormalities could play an additional role in determining these manifestations. We aimed to document the possible NMJ involvement in DM1.

PATIENTS AND METHODS

In order to substantiate this hypothesis we performed low rate repetitive nerve stimulation (RNS) and single fiber electromyography (SFEMG), in 14 DM1 subjects.

RESULTS

RNS resulted abnormal in four patients while SFEMG revealed a pathological jitter in ten. A significative correlation was found between jitter values and decrementing response (p<0.000311; r=0.822).

CONCLUSION

These results suggest a possible involvement of NMJ in DM1.

Variability of multisystemic features in myotonic dystrophy type 1--lessons from Serbian registry

BACKGROUND

Myotonic dystrophy type 1 (DM1) is a rare disease. Creating registry for such a disease is of outstanding importance since it provides us with a full spectrum of the disorder.

AIM

To assess variability of different multisystemic features in a large cohort of patients with DM1.

PATIENTS AND METHOD

Data from the Serbian registry for myotonic dystrophies were used in the study. Final number of included DM1 subjects was 275.

RESULTS

Registry included 53.8% of male patients. Age at enrollment was 47.2 ± 9.9 years, mean disease duration 20.4 ± 9.9 years, and mean CTG repeats number 598.3 ± 269.8.Progression of muscle weakness was pretty slow, slower in proximal than distal muscles, and slower in arms than in legs. Severe ECG abnormality was found in 25.0% of patients and pacemaker was implanted in 9.5%. Lens opacities were observed in 83.5% of DM1 patients and 35.3% had ocular hypotony. Metabolic disturbances were very common, while 19.5% of patients had hypokalemia and 37.8% hypochloremia. Sterility was found in 20.5% of males and 4.1% of females. Cholelithiasis was found in 36.4% of patients and constipation in 29.9%.

CONCLUSIONS

We defined the most common characteristics of our DM1 patients and observed some treatable symptoms that have been neglected previously. Certain findings deserve further investigations in terms of their causes and consequences. Besides this, presented data analysis directs us to make further improvements of the registry.

Peripheral nerve involvement in myotonic dystrophy type 2 - similar or different than in myotonic dystrophy type 1?

INTRODUCTION

Multisystem manifestations of myotonic dystrophies type 1 (DM1) and 2 (DM2) are well known. Peripheral nerve involvement has been reported in DM1 but not in genetically confirmed DM2. The aim of our study was to assess peripheral nerve involvement in DM2 using nerve conduction studies and to compare these results with findings in DM1.

METHODS

We prospectively studied patients with genetically confirmed DM2 (n=30) and DM1 (n=32). All patients underwent detailed neurological examination and nerve conduction studies.

RESULTS

Abnormalities in electrophysiological studies were found in 26.67% of patients with DM2 and in 28.13% of patients with DM1 but the criteria of polyneuropathy were fulfilled in only 13.33% of patients with DM2 and 12.5% of patients with DM1. The polyneuropathy was subclinical, and no correlation was found between its presence and patient age or disease duration.

CONCLUSIONS

Peripheral nerves are quite frequently involved in DM2, but abnormalities meeting the criteria of polyneuropathy are rarely found. The incidence of peripheral nerve involvement is similar in both types of myotonic dystrophy.

Peripheral neuropathy is linked to a severe form of myotonic dystrophy in transgenic mice

Myotonic dystrophy type 1 (DM1) is a multisystem disorder with a variable phenotype. The involvement of peripheral nerves in DM1 disease is controversial. The DM1 animal model DM300 transgenic mice that carry 350 to 500 CTG repeats express a mild DM1 phenotype but do not exhibit motor or sensory pathology. Here, we investigated the presence or absence of peripheral neuropathy in transgenic mice (DMSXL) that carry more than 1,300 CTG repeats and display a severe form of DM1. Electrophysiologic, histologic, and morphometric methods were used to investigate the structure and function of peripheral nerves. We observed lower compound muscle action potentials recorded from hind limb muscles and slowing of sciatic nerve conduction velocity in DMSXL versus control mice. Morphometric analyses showed an axonopathy and neuronopathy in the DMSXL mice characterized by a decrease in numbers of myelinated motor axons in sciatic nerve and in spinal cord motor neurons. Pathologic alterations in the structure of hind limb neuromuscular junctions were also detected in the DMSXL mice. These results suggest that peripheral neuropathy can be linked to a large CTG expansion and a severe form of DM1.

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.