Neuromuscular disorders in childhood: a descriptive epidemiological study from western Sweden

Abstract

A retrospective epidemiological study of neuromuscular disorders was carried out in children born between 1979 and 1994 in western Sweden. The purpose was to determine overall and specific prevalences, overall cumulative incidence and birth incidences of selected disorders. Cases were ascertained from 12 different sources and medical records, investigations and diagnosis were reviewed. We found a point prevalence in the population <16 years of age of 63.1×10⁻⁵ for all neuromuscular disorders and 53.1×10⁻⁵ for inherited neuromuscular disorders. The point prevalence in children of school age was even higher. We found a higher occurrence of hereditary motor and sensory neuropathy, congenital myopathies and mitochondrial encephalo-myopathy, a slightly lower occurrence of Duchenne muscular dystrophy and spinal muscular atrophy and equal occurrence of myotonic dystrophy compared to previous studies in other countries. We conclude that neuromuscular disorders are more common in childhood than has previously been reported.

Introduction

Neuromuscular diseases constitute a complex group of heterogeneous, often inherited disorders. They can be broadly subdivided into disorders mainly affecting the anterior horn cell, peripheral nerve, neuromuscular junction and the muscle fibre. Some multisystem disorders such as myotonic dystrophy and mitochondrial myopathies are traditionally also included [1].

An epidemiological study is important not only for estimating various genetic parameters, e.g. gene frequencies, but also for monitoring the effects of any preventive measures such as genetic counselling, as well as for planning hospital resources, rehabilitation services and social welfare programmes for the handicapped in the community [2], [3]. It also gives valuable information for further research studies.

Population surveys that include all types of neuromuscular diseases are rare and few studies have addressed prevalences in childhood. Previous studies in the whole population have shown variable figures, with a point prevalence of 34.5×10^{− 5} in Northern Ireland [4] and 84.0×10⁻⁵ in Örebro County, Sweden [5], while the childhood prevalence has been estimated to be 24.9–42.0×10⁻⁵ [5], [6], [7].

Western Sweden has a homogeneous health care system with small migration of the population, thus offering unique possibilities of performing epidemiological studies on neurological disorders in childhood, as has been shown in previous studies [8], [9], [10], [11], [12]. The aims of the present study were to estimate overall and specific prevalences of neuromuscular disorders in childhood, and to estimate birth incidences and cumulative incidences of selected disorders with early onset and/or high childhood mortality.