Epidemiology, Survival, and Clinical Characteristics of Inclusion Body Myositis

Abstract

Objective: We performed a population-based study on inclusion body myositis with the primary aims to define the prevalence, survival rate, and incidence, and to investigate the symptom profiles associated with disease duration and sex over a 33-year period.

Methods: Patients diagnosed between 1985 and 2017 in Region Västra Götaland, Sweden, were identified according to the European Neuromuscular Centre diagnostic criteria from 2011.

Results: We identified 128 patients, 89 men and 39 women, with the strict clinicopathological definition of inclusion body myositis. The prevalence was 32 per million inhabitants, 19 per million women and 45 per million men, by December 31, 2017. Mean incidence was 2.5 per million inhabitants and year. Mean age at symptom onset was 64.4 years with quadriceps weakness being the most common presenting symptom followed by finger flexor weakness. Dysphagia was a common presenting symptom being more frequent in women (23%) than men (10%) and was during the disease course reported in 74% of men and 84% of women. Seventy-three patients were deceased, with a mean survival of 14 years from symptom onset. Survival rates from both diagnosis date and symptom onset were decreased compared to the matched population. Twenty-one percent of the patients had an additional autoimmune disease. A cross-sectional analysis of autoantibodies in 50 patients and 28 matched controls showed autoantibodies to cytosolic 5'-nucleotidase 1A in 40% of the patients and 3.6% of controls.

Interpretation: Inclusion body myositis is an autoimmune disease with decreased survival rate and with marked sex differences in both prevalence and clinical manifestations. ANN NEUROL 2022;92:201-212.

FIGURE 1

Inclusion body myositis. Typical muscle biopsy findings (A–D) and typical distribution of muscle atrophy (E). (A) Inflammatory cells in the endomysium surround and invade a muscle fiber (arrows; hematoxylin and eosin). (B) Muscle fibers with rimmed vacuoles (arrows; Gomori trichrome). (C) p62‐positive protein aggregates (arrows) in a muscle fiber. (D) Cytochrome c oxidase (COX)‐deficient fibers (arrows) that appear blue in combined staining for COX and succinate dehydrogenase. (E) Ten years after onset of symptoms, this patient with IBM shows prominent quadriceps muscle atrophy and mild atrophy of the long finger flexor muscles mainly in the left arm. Scale bars correspond to 30 μm. IBM = inclusion body myositis.

FIGURE 2

Map of Region Västra Götaland and flow chart of the study. (A) Region Västra Götaland (VGR; grey) and Gothenburg (dot). Adapted from Region Västra Götaland, VGR Mediebank.²⁵ (B) Flow chart describing the study (men:women). IBM = inclusion body myositis.

FIGURE 3

Cumulative survival, age distribution, and presenting symptoms. (A, B) Sex specific life table estimates of cumulative observed and expected patient survival after IBM diagnosis using period analysis. Effective number at risk shown above the x‐axis. Vertical lines represent 95% confidence intervals. (C) Age at symptom onset and diagnosis. (D) Presenting symptom.IBM = inclusion body myositis.