Neurophysiological and radiological findings in myotonic dystrophy patients

Balance impairment in myotonic dystrophy type 1: Dynamic posturography suggests the coexistence of a proprioceptive and vestibular deficit

Falls are frequent in Myotonic Dystrophy type 1 (DM1), but the pathophysiology of the balance impairment needs further exploration in this disease. The current work aims to provide a richer understanding of DM1 imbalance. Standing balance in 16 patients and 40 controls was tested in two posturographic tests (EquiTest™). In the Sensory Organization Test (SOT), standstill balance was challenged by combining visual (eyes open vs. closed) and environmental conditions (fixed vs. sway-tuned platform and/or visual surround). In the “react” test, reflexes induced by sudden shifts in the support base were studied. Oscillations of the body centre of mass (COM) were measured. In the SOT, COM sway was larger in patients than controls in any condition, including firm support with eyes open (quiet standing). On sway-tuned support, COM oscillations when standing with closed eyes were larger in patients than controls even after taking into account the oscillations with eyes open. In the “react” paradigm, balance reflexes were delayed in patients. Results in both experimental paradigms (i.e., SOT and react test) are consistent with leg muscle weakness. This, however, is not a sufficient explanation. The SOT test highlighted that patients rely on vision more than controls to maintain static balance. Consistently enough, evidence is provided that an impairment of proprioceptive and vestibular systems contributes to falls in DM1. Rehabilitation programs targeted at reweighting sensory systems may be designed to improve safe mobility in DM1.

Paving the way for a better understanding of the pathophysiology of gait impairment in myotonic dystrophy: a pilot study focusing on muscle networks

BACKGROUND

A proper rehabilitation program targeting gait is mandatory to maintain the quality of life of patients with Myotonic dystrophy type 1 (DM1). Assuming that gait and balance impairment simply depend on the degree of muscle weakness is potentially misleading. In fact, the involvement of the Central Nervous System (CNS) in DM1 pathophysiology calls into account the deterioration of muscle coordination in gait impairment. Our study aimed at demonstrating the presence and role of muscle connectivity deterioration in patients with DM1 by a CNS perspective by investigating signal synergies using a time-frequency spectral coherence and multivariate analyses on lower limb muscles while walking upright. Further, we sought at determining whether muscle networks were abnormal secondarily to the muscle impairment or primarily to CNS damage (as DM1 is a multi-system disorder also involving the CNS). In other words, muscle network deterioration may depend on a weakening in signal synergies (that express the neural drive to muscles deduced from surface electromyography data).

METHODS

Such an innovative approach to estimate muscle networks and signal synergies was carried out in seven patients with DM1 and ten healthy controls (HC).

RESULTS

Patients with DM1 showed a commingling of low and high frequencies among muscle at both within- and between-limbs level, a weak direct neural coupling concerning inter-limb coordination, a modest network segregation, high integrative network properties, and an impoverishment in the available signal synergies, as compared to HCs. These network abnormalities were independent from muscle weakness and myotonia.

CONCLUSIONS

Our results suggest that gait impairment in patients with DM1 depends also on a muscle network deterioration that is secondary to signal synergy deterioration (related to CNS impairment). This suggests that muscle network deterioration may be a primary trait of DM1 rather than a maladaptive mechanism to muscle degeneration. This information may be useful concerning the implementation of proper rehabilitative strategies in patients with DM1. It will be indeed necessary not only addressing muscle weakness but also gait-related muscle connectivity to improve functional ambulation in such patients.

Brain imaging in myotonic dystrophy type 1: A systematic review

OBJECTIVE

To systematically review brain imaging studies in myotonic dystrophy type 1 (DM1).

METHODS

We searched Embase (index period 1974-2016) and MEDLINE (index period 1946-2016) for studies in patients with DM1 using MRI, magnetic resonance spectroscopy (MRS), functional MRI (fMRI), CT, ultrasound, PET, or SPECT. From 81 studies, we extracted clinical characteristics, primary outcomes, clinical-genetic correlations, and information on potential risk of bias. Results were summarized and pooled prevalence of imaging abnormalities was calculated, where possible.

RESULTS

In DM1, various imaging changes are widely dispersed throughout the brain, with apparently little anatomical specificity. We found general atrophy and widespread gray matter volume reductions in all 4 cortical lobes, the basal ganglia, and cerebellum. The pooled prevalence of white matter hyperintensities is 70% (95% CI 64-77), compared with 6% (95% CI 3-12) in unaffected controls. DTI shows increased mean diffusivity in all 4 lobes and reduced fractional anisotropy in virtually all major association, projection, and commissural white matter tracts. Functional studies demonstrate reduced glucose uptake and cerebral perfusion in frontal, parietal, and temporal lobes, and abnormal fMRI connectivity patterns that correlate with personality traits. There is significant between-study heterogeneity in terms of imaging methods, which together with the established clinical variability of DM1 may explain divergent results. Longitudinal studies are remarkably scarce.

CONCLUSIONS

DM1 brains show widespread white and gray matter involvement throughout the brain, which is supported by abnormal resting-state network, PET/SPECT, and MRS parameters. Longitudinal studies evaluating spatiotemporal imaging changes are essential.

Brain MRI abnormalities in the adult form of myotonic dystrophy type 1: A longitudinal case series study

This study aimed to verify whether brain abnormalities, previously described in patients with myotonic dystrophy type 1 (DM1) by magnetic resonance imaging (MRI), progressed over time and, if so, to characterize their progression. Thirteen DM1 patients, who had at least two MRI examinations, were retrospectively evaluated and included in the study. The mean duration (± standard deviation) of follow-up was 13.4 (±3.8) years, over a range of 7-20 years. White matter lesions (WMLs) were rated by semi-quantitative method, the signal intensity of white matter poster-superior to trigones (WMPST) by reference to standard images and brain atrophy by ventricular/brain ratio (VBR). At the end of MRI follow-up, the scores relative to lobar, temporal and periventricular WMLs, to WMPST signal intensity and to VBR were significantly increased compared to baseline, and MRI changes were more evident in some families than in others. No correlation was found between the MRI changes and age, onset, disease duration, muscular involvement, CTG repetition and follow-up duration. These results demonstrated that white matter involvement and brain atrophy were progressive in DM1 and suggested that progression rate varied from patient to patient, regardless of age, disease duration and genetic defect.

Functional MRI changes in the central motor system in myotonic dystrophy type 1

Myotonic dystrophy type 1 (DM1) is a multisystemic disease involving multiple organ systems including central nervous system (CNS) and muscles. Few studies have focused on the central motor system in DM1, pointing to a subclinical abnormality in the CNS. The aim of our study was to investigate patterns of cerebral activation in DM1 during a motor task using functional MRI (fMRI). Fifteen DM1 patients, aged 20 to 59 years, and 15 controls of comparable age were scanned during a self-paced sequential finger-to-thumb opposition task of their dominant right hand. Functional MRI images were analyzed using SPM99. Patients underwent clinical and genetic assessment; all subjects underwent a conventional MR study. Myotonic dystrophy type 1 patients showed greater activation than controls in bilateral sensorimotor areas and inferior parietal lobules, basal ganglia and thalami, in the ipsilateral premotor area, insula and supplementary motor area (corrected P<.05). Analysis of the interaction between disease and age showed that correlation with age was significantly greater in patients than in controls in bilateral sensorimotor areas and in contralateral parietal areas. Other clinical and MR characteristics did not correlate with fMRI. Functional changes in DM1 may represent compensatory mechanisms such as reorganization and redistribution of functional networks to compensate for ultrastructural and neurochemical changes occurring as part of the accelerated aging process.

Middle latency auditory-evoked potentials in myotonic dystrophy: relation to the size of the CTG trinucleotide repeat and intelligent quotient

OBJECTIVE

Major components of MLAEPs are thought to originate in the temporal lobe. Absence of the Pb potential has been demonstrated in MLAEPs in Alzheimer's disease and demented Parkinson's disease patients. To validate usefulness of middle latency auditory-evoked potentials (MLAEPs) in evaluating the central nervous system (CNS) involvement of myotonic dystrophy (MyD).

METHODS

MLAEPs were recorded in eight patients with MyD and nine normal control subjects. In the patient group, the size of the CTG triplet repeat expansion within the dystrophia myotonica protein kinase (DMPK) gene and the revised Wechsler Adult Intelligence Scale (WAIS-R) were also assessed.

RESULTS

The latency of the Nb potential showed a significant correlation with the size of the CTG repeat expansion (r=0.734, P=0.036). The Pb latency also tended to prolong according to CTG amplification (r=0.644, P=0.087). The amplitudes of Na and Pa significantly increased compared with those of normal control subjects (P=0.024 and 0.016, respectively). However, they did not correlate with IQ or CTG amplification.

CONCLUSIONS

Abnormal MLAEPs may indicate CNS involvement in MyD. Although the precise generating mechanisms of Nb are unclear, the correlation of Nb latency with CTG amplification suggests that MLAEPs can reflect the extent of genetic abnormality.