Update on sporadic inclusion body myositis

Sporadic inclusion body myositis (IBM) is the most frequent acquired myopathy seen in adults aged over 50 years. Despite the presence of conspicuous inflammatory infiltrates, sporadic IBM is essentially resistant to immunosuppressive treatment and carries an ominous prognosis. In this issue of Brain , two long-term observational studies re-examine the course and prognosis of this enigmatic disease (Benveniste et al. , 2011; Cox et al. , 2011). The paper by Cox et al. (2011) reports on a Dutch cohort of 64 patients with sporadic IBM followed for a median of 12 years, and the paper by Benveniste et al. (2011) describes a French–British cohort of 136 patients followed for a median of 8.6 years (Table 1). View this table:Table 1 Comparison of the main results of the Dutch and French–British sporadic IBM studiesViewed together, the new studies confirm previous observations (e.g., Lotz et al., 1989), and substantiate a number of text book features of sporadic IBM, such as the age of onset (∼60 years, with considerable variation), male preponderance (male/female ratio 67% in the Dutch and 57% in the French/British study), relentless progression (mean/median time to wheel chair 14–16 years) and characteristic distribution of affected muscles (finger flexors, quadriceps, lower leg muscles with relative sparing of shoulder and hip abductors and neck muscles). The mean rate of decline in muscle strength was surprisingly consistent across both studies despite the fact that different methods and scores were used. For example, the mean (±SD) decline in muscle strength per year was 3.5 ± 1.6% by manual muscle testing (using the MRC score; Cox et al. , 2011), 5.4 ± 3.5% by quantitative muscle testing (Cox et al. , 2011) and ∼4% by sporadic IBM weakness composite index (IWCI; estimated from Fig. 1 in Benveniste et al. , 2011). In individual patients, the rate of progression may be …