Neuronal cell loss in the dorsal raphe nucleus and the superior central nucleus in myotonic dystrophy: a clinicopathological correlation

Brain Pathogenesis and Potential Therapeutic Strategies in Myotonic Dystrophy Type 1

Myotonic dystrophy type 1 (DM1) is the most common muscular dystrophy that affects multiple systems including the muscle and heart. The mutant CTG expansion at the 3'-UTR of the DMPK gene causes the expression of toxic RNA that aggregate as nuclear foci. The foci then interfere with RNA-binding proteins, affecting hundreds of mis-spliced effector genes, leading to aberrant alternative splicing and loss of effector gene product functions, ultimately resulting in systemic disorders. In recent years, increasing clinical, imaging, and pathological evidence have indicated that DM1, though to a lesser extent, could also be recognized as true brain diseases, with more and more researchers dedicating to develop novel therapeutic tools dealing with it. In this review, we summarize the current advances in the pathogenesis and pathology of central nervous system (CNS) deficits in DM1, intervention measures currently being investigated are also highlighted, aiming to promote novel and cutting-edge therapeutic investigations.

The actigraphic documentation of circadian sleep-wake rhythm dysregulation in myotonic dystrophy type 1

STUDY OBJECTIVES

The present study aimed at identifying the sleep-wake rhythm in patients with myotonic dystrophy type 1 (DM1) compared to healthy controls.

METHODS

Patients with genetic diagnosis of DM1 and healthy controls underwent a 7-day actigraphic recording and filled out a daily sleep diary to evaluate the sleep-wake rhythm. All participants underwent a physical and neurological examination to exclude conditions interfering with the sleep-wake cycle. Daytime activity, nocturnal sleep, and non-parametric circadian rhythm activity (NPCRA) were analysed.

RESULTS

Twenty-nine patients affected by DM1 were included in the present study and were compared to 16 controls. Considering nocturnal actigraphic data, DM1 patients showed a longer time in bed, sleep period time, actual sleep time, and sleep latency compared to controls. Central phase measurement was significantly longer in DM1 patients than controls. At NPCRA analysis patients showed a lower degree of regularity in the activity-rest pattern compared to controls. Moreover, DM1 patients showed reduced motor activity during daytime and a lower synchronization of the rest-activity rhythm than controls.

CONCLUSIONS

This study documented that patients with DM1 not only present the impairment of nocturnal sleep, but also show a dysregulation of the sleep-wake circadian rhythm; moreover, reduced amplitude of the circadian rhythmicity was also evident in comparison to controls, probably in relation to the reduced diurnal motor activity of patients. These findings add further evidence to the already documented sleep impairment and excessive daytime sleepiness in DM1 patients.

Human brain pathology in myotonic dystrophy type 1: A systematic review

Brain involvement in myotonic dystrophy type 1 (DM1) is characterized by heterogeneous cognitive, behavioral, and affective symptoms and imaging alterations indicative of widespread grey and white matter involvement. The aim of the present study was to systematically review the literature on brain pathology in DM1. We conducted a structured search in EMBASE (index period 1974–2017) and MEDLINE (index period 1887–2017) on December 11, 2017, using free text and index search terms related to myotonic dystrophy type 1 and brain structures or regions. Eligible studies were full‐text studies reporting on microscopic brain pathology of DM1 patients without potentially interfering comorbidity. We discussed the findings based on the anatomical region and the nature of the anomaly. Neuropathological findings in DM1 can be classified as follows: (1) protein and nucleotide deposits; (2) changes in neurons and glial cells; and (3) white matter alterations. Most findings are unspecific to DM1 and may occur with physiological aging, albeit to a lesser degree. There are similarities and contrasts with Alzheimer's disease; both show the appearance of neurofibrillary tangles in the limbic system without plaque occurrence. Likewise, there is myelin loss and gliosis, and there are dilated perivascular spaces in the white matter resemblant of cerebral small vessel disease. However, we did not find evidence of lacunar infarction or microbleeding. The various neuropathological findings in DM1 are reflective of the heterogeneous clinical and neuroimaging features of the disease. The strength of conclusions from this study's findings is bounded by limited numbers of participants in studies, methodological constraints, and lack of assessed associations between histopathology and clinical or neuroimaging findings.

Monoaminergic neuropathology in Alzheimer's disease

None of the proposed mechanisms of Alzheimer's disease (AD) fully explains the distribution patterns of the neuropathological changes at the cellular and regional levels, and their clinical correlates. One aspect of this problem lies in the complex genetic, epigenetic, and environmental landscape of AD: early-onset AD is often familial with autosomal dominant inheritance, while the vast majority of AD cases are late-onset, with the ε4 variant of the gene encoding apolipoprotein E (APOE) known to confer a 5-20 fold increased risk with partial penetrance. Mechanisms by which genetic variants and environmental factors influence the development of AD pathological changes, especially neurofibrillary degeneration, are not yet known. Here we review current knowledge of the involvement of the monoaminergic systems in AD. The changes in the serotonergic, noradrenergic, dopaminergic, histaminergic, and melatonergic systems in AD are briefly described. We also summarize the possibilities for monoamine-based treatment in AD. Besides neuropathologic AD criteria that include the noradrenergic locus coeruleus (LC), special emphasis is given to the serotonergic dorsal raphe nucleus (DRN). Both of these brainstem nuclei are among the first to be affected by tau protein abnormalities in the course of sporadic AD, causing behavioral and cognitive symptoms of variable severity. The possibility that most of the tangle-bearing neurons of the LC and DRN may release amyloid β as well as soluble monomeric or oligomeric tau protein trans-synaptically by their diffuse projections to the cerebral cortex emphasizes their selective vulnerability and warrants further investigations of the monoaminergic systems in AD.

Modafinil for the treatment of hypersomnia associated with myotonic muscular dystrophy in adults: a multicenter, prospective, randomized, double-blind, placebo-controlled, 4-week trial

BACKGROUND

Myotonic muscular dystrophy type 1 (MMD1) is the most common form of adult MD, with a mean prevalence of 1 in 8000. Excessive daytime sleepiness (ie, hypersomnia) is a common complication of MMD1.

OBJECTIVE

The aim of this study was to evaluate the efficacy and tolerability of modafinil for the treatment of hypersomnia in adults with MMD1.

METHODS

This multicenter, prospective, randomized, double-blind, placebo-controlled study consisted of a prerandomization period (90 to 2 days before randomization) and a 4-week randomization period in which patients were assigned to receive either active treatment (modafinil 300 mg/d) or placebo. The study was conducted at 3 clinics in France between February 2000 and June 2002. Adult patients aged > or =18 years, with genetically proven MMD1, an Epworth Sleepiness Scale (ESS) score >10, and a mean latency to sleep onset < or =8 minutes measured by the Multiple Sleep Latency Test (MSLT) were eligible. The primary efficacy end point was the Maintenance of Wakefulness Test (MWT) score at 4 weeks. Secondary end points included the mean MSLT score and scores from the ESS, physician's assessment of the therapeutic effect and the patient's global self-assessment via visual analog scale, the 17-item Hamilton Depression Rating Scale, and the Short Form Health Survey (SF-36) quality-of-life assessment.

RESULTS

A total of 28 patients (15 men, 13 women; mean [SD] age, 40 [12.7] years [range, 18-69 years]; 100% white; modafinil group, 13; placebo group, 15) completed the study without protocol violations. Of the 28 patients with MMD1 included in the analysis, 21 had adult-onset MMD1. At 4 weeks, the mean MWT score was 16.4 (3.3) minutes in the modafinil group and 15.8 (3.8) minutes in the placebo group (P = NS). At the end of the randomization period, there were no significant between-group differences in any secondary outcome. A total of 8 patients (4 in each group) reported > or =1 adverse event, including digestive, neurologic, and skin symptoms. Weight loss was reported in 1 patient (2 kg).

CONCLUSION

In this small study conducted in an adult population with MMD1 and a high prevalence of hyper-somnia, modafinil had no significant effects on daytime somnolence measured using objective MWTs.

Acute respiratory arrest following partial suboccipital cranioplasty for cerebellar ptosis from Chiari malformation decompression

Cerebellar ptosis is a rare complication following Chiari malformation decompression, and generally is the result of a very large suboccipital craniectomy. This can lead to the descent of the cerebellum through the craniectomy defect, which in turn may result in cerebellar herniation through the surgical defect as well as the reestablishment of contact between the cerebellar tonsils and the brainstem. In addition, dorsal adherence of the herniated cerebellum to the dura mater or dural patch and an associated obstruction of cerebrospinal fluid flow at the cervicomedullary junction may ensue. Such a result is not desirable, in that it reproduces or mimics the pathoanatomical relationships that existed prior to the surgical decompression.

Neurofibrillary tangles and deposition of oxidative products in the brain in cases of myotonic dystrophy

Myotonic dystrophy (MyD) is a neuromuscular degenerative disorder that is neuropathologically characterized by minor changes, such as the presence of neurofibrillary tangles (NFT), thalamic inclusions and functional brainstem lesions. In the current study, we conducted an immunohistochemical analysis to examine the distribution of NFT and formation of oxidative products in the brain specimens of 12 patients with MyD. Neurofibrillary tangles were found in the limbic system and/or the brainstem of all the cases examined but there were no senile plaques. The density of distribution of the NFT was not significantly correlated with clinicopathological findings, although cases with fewer NFTin the brain frequently showed sleep disturbances and lack of spontaneity. Nuclear and cytoplasmic immunoreactivities for 8-hydroxy-2'-deoxyguanosine and advanced glycation end products were observed in the glial cells and/or neurons in the brainstem, but not in the cerebral cortex. On the other hand, 10 out of the 12 cases showed cytoplasmic immunoreactivity for 4-hydroxy-2-nonenal-modified protein (4-HNE) in neurons of the temporal cortex and raphe nucleus. Deposition of 4-HNE was also recognized in the hippocampus and mesencephalic central gray matter, but not in the subiculum. The distribution pattern of the immunoreactivity for 4-HNE showed no clear correlation with either the psychological disturbances or the distribution of the NFT. Altered expression of monoaminergic neurons in the brainstem of MyD patients has already been reported, and it is worth noting that most of our cases showed NFT in the brainstem. The selective deposition of 4-HNE in the limbic system and brainstem suggests that lipid peroxidation may be involved in the neurodegenerative process in MyD. Using immunohistochemical analysis to determine the distribution of neurotransmitters in the mesencephalic central gray matter and/or pontine raphe nucleus may help elucidate the relationship between the clinical abnormalities, distribuion of NFT, and 4-HNE deposition in the brain in patients with MyD.

Reduction in excess daytime sleepiness by modafinil in patients with myotonic dystrophy

Patients with myotonic dystrophy frequently suffer from excess daytime sleepiness, which can be a significant cause of disability. Previous studies have indicated that this excess daytime sleepiness is only occasionally due to obstructive sleep apnoea and may be principally of central nervous system origin. Modafinil has been successfully used to treat narcolepsy, a central disorder causing excess daytime sleepiness. We have investigated the use of this drug in myotonic dystrophy patients with excess daytime sleepiness. Patients were recruited from a clinic population on the basis of screening with the Epworth Sleepiness Scale. Patients scoring 10 and above were invited to participate in a randomized double-blind crossover trial of modafinil versus placebo, with four weeks in each arm of the study separated by a 2-week washout period. Patients were assessed by polysomnography at baseline. The primary outcome measures were change in both the Epworth Sleepiness Scale and a modified Maintenance of Wakefulness Test, which were measured at the start of each arm of the trial and in week 3 of each intervention period. In agreement with previous smaller studies, sleepiness is not correlated with CTG expansion size. Treatment with modafinil showed a non-significant reduction in median Epworth Sleepiness Scale. However, the median Maintenance of Wakefulness Test score was prolonged by treatment (31.7-40 min, P=0.006). There were no significant adverse cardiac effects of the drug in this group of patients (resting 12 lead and 24 h ECG monitoring). Selected patients with myotonic dystrophy and excess daytime sleepiness may benefit from modafinil. In this patient group the Epworth Sleepiness Scale may not be the most reliable measure of sleepiness. Despite the potential for cardiac disease in these patients, the drug was well tolerated with no adverse effects.