Bethlem myopathy: early-onset benign autosomal dominant myopathy with contractures. Description of two new families.

Bethlem myopathy is an apparently rare early-onset benign autosomal dominant limb-girdle myopathy with contractures of the fingers. To determine whether this disorder is unrecognized rather than rare we used muscle computerized tomography (CT) and isokinetic muscle testing and assiduously sought contractures of the fingers in relatives of two patients with the disease. CT showed that muscle impairment was mild but more diffuse than clinically apparent and showed an unexpected progressive degeneration of lumbar paravertebral muscles. The isokinetic test showed that the quadriceps was more involved that the hamstrings. In addition we found that contractures of the last four fingers progressed centripetally with age from the distal interphalangeal joints to the wrist. As a result we proved that 15 of the 21 examined subjects had the disease, 7 of them being unaware that anything was amiss. Careful examination may reveal that Bethlem myopathy is more common than is now thought.