Loss of strength and functional decline in Duchenne's dystrophy.

Clinical tests of strength and function were performed on 27 ambulatory patients with Duchenne's dystrophy every three months for 2 1/2 years. Linear decline of strength remains a fundamental characteristic of Duchenne's dystrophy. Although generally considered a homogeneous disease, our patients showed a broad spectrum of disability. Current tests of functional ability are poor measures of disease progression during most of the ambulatory period, since efficiency is maintained despite continuous decline in muscle strength. However, after this "latent" phase, failure of certain functions paralleled muscle deterioration closely, since task loss occurred within a narrow range of composite muscle strength. Finally, data on changes in body weight showed that most patients were excessively thin rather than obese. It is concluded that manual muscle strength testing remains the most valid method of monitoring disease progression and must be included in patient assessment.