Background Large-scale electronic primary care datasets can provide up-to-date, accurate epidemiological information on rarer diseases. In the UK, approximately 70,000 people are estimated to be living with neuromuscular disease (NMD), but this approximation is over 10 years old and used historical estimates from different sources. While GPs are unlikely to make NMD diagnoses themselves, specialist diagnoses from hospital discharges and clinic letters are well recorded and electronically searchable within primary care records. The recent expansion of the Clinical Practice Research Datalink (CPRD) allows timely reporting on the recorded incidence and prevalence of NMD in the UK over the last 20 years.
Methods A harmonised dataset of CPRD GOLD and Aurum was developed to provide annual denominators of actively registered patients between 2000 and 2019. A Read code hierarchy was developed for a wide range of NMDs; the database was then searched electronically to estimate incidence and (lifetime) prevalence rates in each year. To compare trends over time, rates were age standardised to the most recent CPRD population (2019).
Results The combined CPRD database contained approximately 13 million patients actively registered in each year. By 2019, 28,230 active patients had ever received a Read code for one of the NMDs (223.6 per 100,000), which would scale up to approximately 149,000 people in the UK. Lifetime prevalence rates per 100,000 were higher among males (239.0) than females (208.3). The most common classifications were Guillain-Barre syndrome (40.1), myasthenia gravis (33.7), muscular dystrophy (29.5), Charcot-Marie-Tooth (29.5) and inflammatory myopathies (25.0). Since 2000, overall prevalence grew by 63% but incidence remained steady over time. All age groups showed an increase in prevalence, with the largest increases seen at older ages (≥65-years). Among individual conditions since about 2008, incidence of myasthenia gravis has been steadily rising while new cases of muscular dystrophy fell over the same period.
Conclusions Lifetime recording of many NMDs on primary care records exceeds current estimates of people living with these conditions; these are important data for health service and care planning. Temporal trends suggest this number is steadily increasing and there may be twice as many people living with these conditions than currently thought. While this may be partially due to increases in recording, it cannot be simply explained by new cases as incidence is largely unchanged over time. The increase in prevalence among older ages suggest increases in life expectancy among those living with NMDs may have taken place.
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