Alteration of Lactate Production During Incremental Exercise in Myotonic Dystrophy Is Not Dependent by Catecholamine Increase

Abnormalities of mitochondria have been reported in Myotonic Dystrophy (MD). Adrenergic activation is one of the major factors influencing exercise lactate production in healthy subjects. In order to assess the role of such activation in MD, we compared blood catecholamine levels to those of lactate during an incremental bicycle exercise in 9 MD patients and 6 controls. The lactate values reached significantly higher levels in patients than in controls at rest (2.91 ± 0.58 vs 1.44 ± 1.14 mmol/l, p<0.01, in average), at the anaerobic threshold (4.43 ± 1.11 vs 2.62 ± 0.73 mmol/l, p<0.05), at exercise peak (6.64 ± 1.34 vs 3.90 ± 0.99 mmol/l, p< 0.05) and at recovery (3.21 ± 0.94 vs 1.91 ± 0.19, p<0.01). Furthermore, the anaerobic lactate threshold (LT) in MD was acquired at lower workload (mostly in a range between 30 % and 50 % of the predicted normal maximal power output) compared to controls (60-70%), this suggesting an early activation of the anaerobic metabolism in MD patients. On the contrary, catecholamine levels were not significantly different between patients and controls. These results indicate that abnormal lactate production in MD is independent of the adrenergic response to exercise and suggest a direct involvement of skeletal muscle o-xidative metabolism in MD

Disruption of sleep-wake continuum in myotonic dystrophy type 1: Beyond conventional sleep staging

Sleep disruption and excessive daytime sleepiness are well recognised symptoms in myotonic dystrophy type 1 (DM1), where a central dysfunction of sleep-wake regulation may play a pivotal role. Few studies evaluated sleep macrostructure in DM1, but none investigated more refined sleep variables. Eight DM1 patients (6 male, aged 20-50 years) and 10 healthy controls (7 male, aged 22-67 years) underwent nocturnal polysomnography and multiple sleep latency test. Sleep stages and events were scored according to standard criteria; sleep microstructure was analyzed through cyclic alternating pattern. Relative and absolute delta powers were computed for whole non REM and each non REM period. DM1 patients showed increased REM sleep and decreased N2. N3, although not significantly, was increased. Three patients, but no controls, had sleep-onset REM period in nocturnal sleep. DM1 patients showed slower delta power dissipation across the night, and increased sleep instability (CAP rate). Multiple sleep latency tests showed shorter sleep latencies, five patients presenting at least one sleep-onset REM period and, when including also night sleep, two sleep-onset REM periods. Our data confirm a narcoleptic-like phenotype in DM1 with a prominent REM sleep dysregulation, that may account for daytime sleepiness, together with increased sleep instability and impaired delta power dissipation that seem peculiar of the disease

Early left ventricular structural myocardial alterations and their relationship with functional and electrical properties of the heart in myotonic dystrophy type 1

Background: Conduction disturbances and arrhythmias characterize the cardiac feature of myotonic dystrophy type 1 (MD1), and a myocardial involvement has been suggested as part of the cardiac disease. The aim of the study was to investigate the role of novel ultrasonic techniques, such as integrated backscatter (IBS) and color Doppler myocardial imaging (CDMI), in the assessment of the subclinical functional and structural myocardial involvement in patients with MD1.Methods: Thirty-one patients with MD1 (MD1 group) without known heart failure were evaluated and compared with 31 healthy, age-matched controls. In all patients, 19 conventional and 28 new echocardiographic parameters (14 tissue Doppler, 10 CDMI, and 4 IBS indexes) were analyzed.Results: In regard to ultrastructural left ventricular (LV) properties, a significantly higher IBS echointensity was found at the septum level in the MD1 group, with a statistically significant correlation with MPI (myocardial performance index) (r = 0.34; P = .05) and PR interval duration (r = 0.40; P = .05). In regard to LV systolic function, the MD1 group showed an early alteration of systolic function compared with controls, evidenced by a significant higher MPI and lower peak strain, strain rate, and cyclic variation index (CVI). In regard to LV diastolic function, the MD1 group showed an early alteration of diastolic function compared with controls, evidenced by lower tissue Doppler imaging, E/A, and E/A strain rate, with a statistically significant inverse correlation to the muscular disability rating scale. On receiver operating characteristic curve analysis, MPI and CVI showed the highest discriminating ability to differentiate the hearts of patients with MD1 from healthy subjects.Conclusion: Highly sensitive ultrasonic techniques can detect early functional and structural alterations of the LV myocardium in patients with MD1. (J Am Soc Echocardiogr 2009; 22: 1173-9.