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. 2018 Sep 17;2(2):rky035.
doi: 10.1093/rap/rky035. eCollection 2018.

Increasing incidence of adult idiopathic inflammatory myopathies in the City of Salford, UK: a 10-year epidemiological study

Matthew J S Parker  1   2 , Alexander Oldroyd  2   3 , Mark E Roberts  4 , William E Ollier  1   2 , Robert P New  5 , Robert G Cooper  5   6 , Hector Chinoy  1   2
Affiliations

Increasing incidence of adult idiopathic inflammatory myopathies in the City of Salford, UK: a 10-year epidemiological study

Matthew J S Parker et al. Rheumatol Adv Pract. .

Abstract

Objectives: The aim was to identify and characterize all incident adult cases of idiopathic inflammatory myopathies (IIM) between 1 January 2007 and 31 December 2016 in the City of Salford, UK.

Methods: Adults first diagnosed with IIM within the study period were identified by: a Salford Royal NHS Foundation Trust (SRFT) inpatient episode IIM-specific ICD-10 coding search; all new patient appointments to SRFT neuromuscular outpatient clinics; and all Salford residents enrolled within the UKMYONET study. All patients with definite IIM by the 2017 EULAR/ACR classification criteria were included, as were probable cases if consensus expert opinion agreed. Cases were excluded if <18 years of age at disease onset, if they did not meet probable criteria or when probable but expert opinion concluded a non-IIM diagnosis.

Results: The multimodal case ascertainment identified 1156 cases which, after review and application of exclusion criteria, resulted in 32 incident cases during the study period. Twenty-three of 32 were female, with a mean age of 58.1 years. The mean incidence of adult IIM was 17.6/1 000 000 person years, and higher for females than for males (25.2 vs 10.0/1 000 000 person years, respectively). A significant incidence increase over time was apparent (13.6 vs 21.4/1 000 000 person years; P = 0.032). Using EULAR/ACR classification criteria, the largest IIM subtype (21/32) was PM, followed by DM (8/32), IBM (2/32) and amyopathic DM (1/32). Expert opinion subtype differed from EULAR/ACR classification criteria in 19/32 cases.

Conclusion: The incidence of adult IIM in Salford is 17.6/1 000 000 person years, higher in females, and is increasing over time. Disagreement exists between EULAR/ACR-derived and expert opinion-derived IIM subtype assignments.

Keywords: DM; PM; classification; inclusion bodies; inflammatory muscle diseases; inflammatory myopathy; myositis.

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Figures

<sc>Fig</sc>. 1
Fig. 1
The annual incidence of idiopathic inflammatory myopathies in the City of Salford, UK Grey bars illustrate 95% confidence intervals; dashed green line illustrates linear trend line with accompanying coefficient of determination
<sc>Fig</sc>. 2
Fig. 2
The relationship between EULAR/ACR classification criteria-assigned idiopathic inflammatory myopathy subtype and clinician-assigned idiopathic inflammatory myopathy subtype ADM: amyopathic DM; ASS: anti-synthetase syndrome; IMNM: immune-mediated necrotizing myopathy; OM: overlap myositis
See this image and copyright information in PMC

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