Subclinical semitendinosus and obturator externus involvement defines an autosomal dominant myopathy with early respiratory failure.

We recently described a dominant limb myopathy characterised by early respiratory failure whilst affected individuals were still ambulant (autosomal dominant myopathy with early respiratory failure). Early diagnosis and exclusion of this disorder is difficult because of the insidious onset in late adult life and the highly selective muscle involvement, both clinically and pathologically. We performed muscle magnetic resonance imaging on seven cases of autosomal dominant myopathy with early respiratory failure (age range 37-66 years, 4 male) and show selective early involvement of semitendinosus and obturator externus on magnetic resonance imaging that cannot be detected clinically, with different rates of progression in closely related muscles. These findings are specific to autosomal dominant myopathy with early respiratory failure and enable early non-invasive diagnosis for individuals at risk.