The Duchenne muscular dystrophy population in Denmark, 1977–2001: prevalence, incidence and survival in relation to the introduction of ventilator use
Introduction
A number of observational studies over the past 25 years have suggested a life prolonging effect of mechanical ventilation of Duchenne muscular dystrophy (DMD) patients [1], [2], [3], [4], [5], [6], [7], [8]. A consensus to recommend this treatment now appears to prevail among professionals in the field [9]. However, strictly scientific evidence of a life-prolonging effect would in theory be obtainable only through a controlled clinical trial but such an experiment seems neither ethically correct nor practically feasible.
In Denmark mechanical ventilation of DMD patients occurred only sporadically before the end of the 1980s. In 1991 two centres for the management of chronic respiratory insufficiency in neuromuscular disorders and other rare diseases were created. The aim was to centralize a specialized and infrequent treatment in order to optimize the gathering of experience and strengthen research in the area.
Today, home mechanical ventilation of DMD patients has become common in Denmark. The patient typically starts at the age 16–19 years with nocturnal nasal ventilation, which is replaced by a tracheostomy some years later when the vital capacity has deteriorated to a degree that requires assisted ventilation round the clock.
In 1971 Muskelsvindfonden was founded as a pressure group independent of the medical establishment by patients with neuromuscular diseases. During the 1980s Muskelsvindfonden advocated improved respiratory care including the possibility of the patient himself to choose tracheostomy [10]. Doctors in key positions were opposed to this treatment, which they considered unethical. Furthermore, efforts to centralize a specialized respiratory management conflicted with strong interests of regional health care authorities. Bureaucracy was a player too.
The purpose of this study was to calculate the prevalence, incidence, mortality and the use of mechanical ventilation in the DMD population in Denmark during the period 1977–2001, in order to estimate the influence of mechanical ventilation on survival and further, to view the introduction of mechanical ventilation in the patient group in the light of decision-making processes and main players in order to assess the influence of Muskelsvindfonden.
The period of study was determined to obtain data before and after the establishment of the respiratory centres. Furthermore, a specific national registration of DMD patients came into effect around 1977 after the foundation of the Institute of Neuromuscular Diseases September 1, 1976 on the initiative of Muskelsvindfonden.
Section snippets
Design
The study comprised two components, an observational epidemiological and an organizational, which were synthesized by the interpretation of coincidences between the introduction and use of mechanical ventilation on the one hand and epidemiological trends in the DMD population on the other.
Population
The study population was the male Danish population in the period January 1, 1977 to January 1, 2002 and Danish live born males, 1972–2001. Population figures were obtained from StatBank Denmark (reference
Prevalence
The overall prevalence of DMD patients in absolute numbers increased from 78 on January 1, 1977 to 145 on January 1, 2002. The overall prevalence proportion rose from 3.1 to 5.5 per 105 males (Table 2).
Incidence
One hundred and fifty-nine of 243 DMD patients were included in the calculations of incidence as six born abroad were excluded and 78 were prevalent at the beginning of the study period. The standardized incidence rate per 105 years at risk among boys aged 0–9 years remained consistent across the
Discussion
As indicated by the selection procedure the number of DMD patients in the study period may exceed the 243 verified cases. Most likely the selection is inadequate at the beginning of the period when the Institute of Neuromuscular Diseases was not yet known nationwide. The prevalence proportions in the age group 15–19 years, and perhaps age group 20–24 years as well, in the first 4 years of the study period seem underestimated (Table 2).
Mean prevalence and incidence figures in a world survey are
Acknowledgements
Financial support has been obtained from Muskelsvindfonden and the Institute of Neuromuscular Diseases. The authors wish to thank the Respiratory Centres at the State University Hospital and Aarhus University Hospital for kind cooperation.
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