[Cardiac, respiratory and sleep disorders in patients with myotonic dystrophy]

Abstract

Myotonic dystrophy (MD) is a genetically determined disease with autosomal dominant mode of inheritance. Relatively recently, MD has been divided into two sub-types (MD1 and MD2). Clinical symptoms of MD1 result from the expansion of a (CTG)n trinucleotide of the gene coding for serine/threonine protein kinase and clinical symptoms in MD2 are associated with the expansion of (CCTG)n in I intron of the zinc-finger protein 9 (ZNF9). Myotonic dystrophies MD1 and MD2 are multisystem diseases with numerous symptoms and high interfamily variability, resulting from the fact that different organs are affected. Until now the mechanisms that lead to the damage of the central and peripheral nervous systems, heart muscle and endocrine system have not been fully understood. Symptoms that are characteristic of MD1 and MD2 are myotonic symptom, muscular weakness and muscular atrophy. In MD2, muscular weakness and muscular atrophy are expressed more significantly in proximal segments, which is a differentiating factor for patients with MD1 who have muscular weakness and muscular atrophy in distal segments. Apart from myotonia and symptoms of skeletal muscle damage, the disease affects smooth muscles, heart muscle and the central nervous system, causing cataract, endocrine disorders, cognitive dysfunctions, intellectual and personality disturbances as well as sleep disordered breathing with nocturnal hypoventilation, obstructive, central and mixed apneas and hypopneas. The symptoms of sleep disordered breathing is fatigue, reduced cognitive performance and excessive daytime sleepiness. The pathophysiology of the breathing disorders includes weakness of the respiratory muscles and disorder of the respiratory drive. Of some interest are the works in which authors evaluated the incidence and character of abnormalities in the peripheral and central nervous systems. It has been shown that the number of CTG-repeats in the same person with MD1 is not stable over time and may increase, which leads to disease progression and new clinical symptoms. Cardiologic disorders associated with myotonic dystrophy are common and are part of the clinical picture of the disease. The dominant pathology are conduction disturbances and cardiac arrhythmias. It is estimated that 40 to 80% of patients with MD1 have abnormalities in ECG, and rapid supra-ventricular and ventricular cardiac arrhythmias are the second common cause of death in patients with MD1. Unfortunately, most of these pathologies are asymptomatic until life-threatening conduction blocks and/or supra-ventricular tachyarrhythmias occur. Sometimes, prodromal symptoms such as collapsing, fainting or feeling of palpitation occur and they should always draw attention of the treating doctor of a patient with muscular dystrophy. This paper is aimed at characterizing some common cardiologic and sleep related respiratory disorders of patients with myotonic dystrophy which if not recognized in good time may lead to sudden death.