Bethlem myopathy is a condition that mainly affects skeletal muscles, which are the muscles used for movement. People with this condition experience progressive muscle weakness and develop joint stiffness (contractures) in their fingers, wrists, elbows, and ankles that can restrict movement. Approximately two-thirds of people with Bethlem myopathy over age 50 will need to use a walker or wheelchair.
The features of Bethlem myopathy can appear at any age. Some individuals have signs of the disorder even before birth, most commonly decreased fetal movement. Other affected individuals develop symptoms soon after birth, including low muscle tone and a stiff neck that causes the head to lean to one side (torticollis). People whose symptoms appear in childhood may experience delayed developmental milestones, such as sitting or walking. Others do not develop features of the condition until late adulthood.
Some people with Bethlem myopathy have skin abnormalities such as small bumps called follicular hyperkeratosis that develop around the elbows and knees; soft, velvety skin of the palms and soles; and wounds that split open with little bleeding and widen over time to create shallow scars.
Testing for this condition involves either a DNA test or a skin biopsy.